human centipede experiment

The Twisted Nazi Experiments That Inspired ‘The Human Centipede’

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The Big Picture

The Human Centipede films are known for their depraved and disgusting content, but they have also sparked a fascination with body horror.
The trilogy was actually inspired by horrific events from Nazi Germany, particularly the experiments conducted by Dr. Josef Mengele.
The filmmaker, Tom Six, wanted to create a discomforting film that was different from typical horror genres, and the concept for the Human Centipede originated from a disturbing joke about punishment for child molesters.

Although disgusting, the Human Centipede films have created a deep fascination with the gross and twisted world of body horror . If you know, you know; if you don't, you're likely more well-adjusted than the rest of us. Directed by Tom Six , The Human Centipede is a trilogy of films — released in 2009, 2011, and 2015 — widely known as depraved and, well, icky. It's the story of three people trapped by a deranged German surgeon after their car breaks down. This surgeon has a sick, twisted desire to torture them in various, inhumane ways and eventually turn those three people into a human centipede. How does he plan to do that, you might ask. He conjoins them through their gastric systems , of course! In simple terms, he puts them on their hands and knees and sews them together from mouth to anus.

But did you know that The Human Centipede was actually inspired by some horrific history ? After reading the description of the film, it seems far-fetched that something of that abominable nature would be based on anything real — but it is! Between the heinous history of Nazi Germany and a joke between Tom Six and his friends, The Human Centipede was born.

The Human Centipede (First Sequence)

A mad scientist kidnaps and mutilates a trio of tourists in order to reassemble them into a human centipede, created by stitching their mouths to each others' rectums.

Is ‘The Human Centipede’ Based on a True Story?

During the Nazi reign of Germany , some incredibly questionable doctors and surgeons were performing experiments on victims in concentration camps. One of these doctors in particular was Dr. Josef Mengele. According to the Chicago Tribune , Mengele is accused of killing around 400,000 Jews at Auschwitz in a span of two years. During a testimony at the Yad Vashem Holocaust Memorial in Jerusalem, 30 survivors came forward to reveal the horrors of what Mengele would do. These survivors are only alive because they were twins. Mengele practiced eugenics, which is a set of practices where the main goal is to improve the genetic quality of the human population , typically by excluding or attempting to eradicate groups that were said to be "inferior." For eugenicists, twins were the perfect subject because their differences were only due to behavior and not genetics . Ultimately, this means they felt as if they could wipe out what they deemed to be non-desirable characteristics through selective breeding. Based on that information, we can conclude that Mengele was a real piece of work.

The survivors shared in their testimony some of the horrors that Mengele performed. One of those was ripping an infant from its mother's womb and throwing the fetus into an oven because it wasn't a twin. Another recounted him pinning eyeballs to the wall like a sadistic mural. Many of Mengele's subjects who survived were subject to deep-seated trauma and even sometimes lifelong disfigurement. Mengele was known to try to force sterilization , inject diseases, amputate limbs, and even sew twins together to replicate conjoined twins. It seems very clear that the demented surgeon in The Human Centipede , Dr. Josef Heiter ( Dieter Laser ) was named after and inspired by Dr. Josef Mengele.

Roger Ebert Simply Refused to Rate ‘The Human Centipede’

The horror movie proved to Ebert that some films simply live outside the standard star ratings.

‘The Human Centipede’ Was Also Inspired by a Joke

Tom Six told IndieWire that he was assuredly wanting to create an uncomfortable film . That is the understatement of the year, Mr. Six! He attributes the success and popularity of the film to the fact that it is a new and fresh idea that isn't a ghost story or a slasher. In a n interview with The Guardian , Six revealed that he doesn't do morals, and the contents of The Human Centipede trilogy really showcase that. The other inspiration for The Human Centipede came from a joke between him and a friend of his . The joke in question is just as appalling as the film itself in a very true Tom Six fashion. That joke is about how the greatest punishment for a child molester would be being sewn to the anus of an overweight truck driver.

What Else Did Tom Six Want ‘The Human Centipede’ To Convey?

Deiter Laser as Josef Heiter looking directly at the camera while standing while holding a staff under his arm

The sensationalism of The Human Centipede can make it difficult to understand there's more within the film. When you see a monstrosity on screen followed by lines of "feed her!" fully knowing what's going to happen, it's a little difficult to get your brain to think critically . The first sequence of The Human Centipede strongly takes a look at the concept of impurity, and not just because of the intestinal content. The Nazi regime focused solely on the existence of impurity and how, in those leaders' and doctors' eyes, they had to get rid of it. Where the Nazis viewed anyone not of the "master race" as impure, Six tackled the concept of their history being corrupt and full of monsters.

In the rest of the trilogy, metaphors are addressed in slightly different ways . The second sequence showcases how the line between fantasy and reality can sometimes blur, especially regarding obsessive adoration. The antagonist of the second film is obsessed with the first film and Dr. Heiter's work, so he sets out to create his own human centipede. The final sequence brings back Dr. Heiter's character, but this time as a prison warden who co-conspires with his peers to create an even larger human centipede from prisoners after watching the first and second films. The third film tackles issues ranging from racism, xenophobia, violence, and prison systems.

The Human Centipede has become a test of endurance in the horror world. It challenges anyone to sit through the whole thing without wanting to be sick, covering your eyes, or turning it off. Many critics will pin the movie as having no plot and being too disgusting to enjoy, but those viewers who are really into body horror may marvel at just how absolutely insane these films are. The Human Centipede may take gross-out horror to the extreme, but its real-life inspirations materialize just how toxic society can be in the wrong hands . If you dare, you can watch for yourself, but it may be best to keep a barf bag handy.

The Human Centipede is currently available to rent or buy on Amazon Prime in the U.S.

Watch on Amazon Prime

Movie Features
The Human Centipede

True story behind The Human Centipede - its link to Nazi Germany as director talks new film

The plot of the controversial film is steeped in horrifying history, here's what inspired the graphic movies

14:46, 24 May 2018
Updated 14:00, 28 May 2020

The iconic Dutch horror film The Human Centipede by director Tom Six was released in 2009 and produced some rather visible reactions.

It was condemned for its revolting and grotesque scenes , which showed a German surgeon who kidnaps three tourists, tortures them, before he joins them surgically, mouth to anus, forming a "human centipede" - a conjoined triplet.

The controversy would continue with Six's sequel to the film The Human Centipede 2 (Full Sequence), which was only released in the UK in 2011 after substantial cuts and edits, after the British Board of Film Classification (BBFC) refused to give the film an 18 certificate unless the film cut a large number of graphic scenes - including masturbation with sandpaper, rape with barbed wire, and the brutal murder of a newborn baby.

The final film in the torture trilogy The Human Centipede 3 (Final Sequence) was critically panned and derided for its enjoying of sexual violence and self-serious focus on punishment in the criminal justice system.

Tom Six's next film is psychological thriller The Onania Club, which is due out later this year, so we think this would be the perfect time to look at what inspired the Dutch director's disturbing iconic trilogy.

The Human Centipede

There were some key inspirations for Six's original horror flick, but some are much more serious than others.

The main inspiration for the film came from a joke that Six had told to his friend where he explained a punishment for child molesters which would see their mouths stitched to the anus of a fat truck driver.

As the film germinated in Six's mind, he took inspiration from real life and abhorrent episodes in recent history.

Six's chief historical inspiration was the Nazi experiments conducted on Concentration Camp prisoners in World War Two, including the diabolical experiments of Dr. Josef Mengele.

The experiments saw prisoners across Europe forced to participate in tests that mostly ended in death, trauma, disfigurement, and permanent disability.

The vile examples of medical torture included tests on twins, with twins being forcibly sewn together to become conjoined, and dying eyes in twins to see how they would react. If one twin died in the experiment, the other would always be killed.

The monsters also conducted bone, muscle, and nerve transplants on prisoners without the use of anesthesia.

There were also tests of new drugs, weapons (such as mustard gas and poisons) and sterilization on prisoners, against their will, which would have long-lasting medical reprecussions.

The film also features victims of multiple nationalities to represent countries involved in World War Two, with the evil Dr Josef Heiter (Heiter meaning "cheerful" in German) representing the Nazi German psyche.

Finally, Six was also inspired by the previous cinematic offerings from visceral directors David Cronenberg and David Lynch, and also the Dutch iteration of the iconic reality series Big Brother.

The Human Centipede 2 (Full Sequence)

The sequel film took things to an even darker place, with much more graphic scenes and more disparate inspirations.

Six decided to make the plot very meta: it would focus on a fan of the first film who would then conduct his own sadistic experiments and punishments.

The chief inspiration for this decision was Six's fascination with copycat serial killers, who usually start as fans of the original killer.

The term copycat killer was coined after the killings by iconic and mysterious serial killer Jack the Ripper sparked a number of similar murders.

The film Natural Born Killers starring Woody Harrelson is often blamed for sparking copycat killings, after being loosely based on serial killers Charles Starkweather and Caril Ann Fugate.

Up to 12 murders were linked with being inspired by that film, including teenage couple Benjamin Darras and Sarah Edmondson, who described themselves taking LSD and watching the film on repeat before killing 3 people and paralysing another.

The character of Martin Lomax is a short, obese man who is mentally challenged and becomes obsessed with the first film, before setting out to create a larger human centipede than the 3 people sewn together in the first film.

The Human Centipede 3 (Final Sequence)

The last film saw Six want to return to the theme of the original joke that inspired the film series: punishment.

It was set in a prison where a psychopathic prison warden and his accountant (each played by the actors behind the villains of the first two films) who decide to inflict brutal torture upon the inmates of the prison - including mass castration, cannibalism, genital mutilation and a massive five-hundred person sized centipede.

The film had a much more satirical tone, but this was one of the many aspects of the piece that critics and fans slammed.

With the Governor (played by Hollywood star Eric Roberts) approves the torture as being "what America needs" at the end of the film, things enter a more dystopian territory - as we see extreme values in corporal punishment come bleed into culturally-approved torture.

Corporal punishment is always a controversial topic, but its pros and cons were dealt with no sympathy here.

Six likely saw inspiration in infamous prisons that were the site of torture, such as the US base at Guantanomo Bay in Cuba, and of course the Nazi concentration camps that were the chief basis of the first film.

We expect Tom Six's next film to be just as provocative.

The Onania club will be released later this year.

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Being Human

Was The Human Centipede Real? From Horror To Reality

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One of the most bizarre movies in history raised questions to viewers, with many asking, “Was the human centipede real?”

But what is the real story behind the human centipede? Are the events depicted in the movie based on real-life events, or are they all the imaginations of a twisted writer?

The human centipede was inspired by horrific Nazi experiments shared by survivors of concentration camps, but it is not exactly as depicted in the movie.

Tom Six, the director, attributes the movie idea to a joke between his friends, the joke being how the best punishment for child molesters would be to be sewn to the anus of an overweight truck driver.

Metaphors and Theories About The Human Centipede

People knowing that True events inspired the Human Centipede contributed to its large following, but most people didn’t give it much thought. What were the directors using the movie to convey to their audience? Let’s find out;

During the Nazi regime, several reports of German scientists attempted to conduct heinous experiments on humans.

Dr. Josef Mengele’s experimental endeavors were particularly noteworthy. These were actual stories about Human Centipede-like experiments.

Some tests were conducted on twins forcibly sewn together to simulate conjoined twins who suffer a similar fate.

Other experiments, including experimental bone, skin, muscle, and nerve transplants, were frequently performed without anesthetic.

New surgical treatments such as brain surgery and sterilization were also attempted with gusto, frequently with fatal results or, far worse, long-term medical consequences.

To emphasize the connection, the principal character, the scientist conducting these tests, is also appropriately named Dr. Josef Heiter. The Human Centipede is referring to these genuine accounts of heinous experiments.

What Made The Human Centipede Stand Out To Most Audiences?

It took a much darker and twisted approach to its story and characterization that made the movie create a bigger splash in pop culture.

There’s no disputing that this contentious film left an impression. The Human Centipede did a fantastic job of grossing out spectators, but this picture left such a lasting impression because it taps into a terror that the horror genre isn’t used to.

The story revolves around a successful conjoined twin surgeon who develops an unhealthy obsession with building the world’s first human centipede: stitching three individuals in a line, ass-to-mouth.

Lindsay, Jenny, and Katsuro are forced to participate in Dr. Josef Heiter’s macabre vision of sewing three individuals together by their gastrointestinal systems. Being linked to another individual for the rest of your life is terrifying.

They can’t just return to their everyday lives of family, work, and fun; they’re stuck with a sick man without regard for their humanity . Lindsay, Jenny, and Katsuro are serving a life sentence in the confines of Dr. Heiter’s home.

They even lost the right to simply eat, sleep, and breathe as prisoners can do behind bars. With death, you are not subjected to physical and emotional torture daily by some maniac who regards you as a pet.

For example, Jaime Lee Curtis’ Laurie Strode is a cherished final girl, but her character lacks depth when appearing in the first Halloween film.

That storytelling method is prevalent in The Human Centipede since we know little about Lindsay, Jenny, and Katsuro. Still, their characters are well-crafted enough that they don’t appear unlikeable.

However, leaving an aura of mystery around them makes the incident more unpredictable. Though we are unaware of who they are, it’s easy to sympathize with them because Dr. Heiter has wicked intentions.

Their panic and fear quickly connect with viewers. The sensation of dread overrides our emotions with each passing second; the drama and tension stem from the psychological torment that these folks are subjected to.

They’re terrified because a twisted, insane man with a similarly unknown past has thrown off the status quo. When the human centipede is fully formed, the fear increases because it is now more difficult for these three to flee.

This could quickly have devolved into a gross-out creature in David Cronenberg’s The Fly or John Carpenter’s The Thing. Still, Tom Six skillfully avoids shattering the illusion of reality by not going beyond this strategy.

It’s why the first film in his three-part trilogy is still the finest, as Six chose the Texas Chainsaw Massacre path, focusing on the psychological aspect rather than the blood and gore.

The Dark Cinematic Choices Behind The Human Centipede

The Human Centipede was a revolutionary film that made waves in Hollywood, and it is still featured in many pop culture references an entire decade after its release.

This primarily owes to its dark and twisted approach to telling its story, which made it gory and timeless.

The Human Centipede, although lacking the subtlety of Wes Craven films or The Wicker Man, makes it evident that historical similarities are in the visual story that merits greater examination.

There is an implicit attempt to familiarize viewers with the certainty of situations that result in the loss of self-respect, comfort, and life.

The sense of approaching doom affects various victims differently, and their behaviors reveal fascinating details about who they are as people.

The lack of nuance and the deep dive into plain sensationalism bolsters this comparison significantly. Six practically dares the audience to turn away, and many do.

However, suppose you keep your eyes on the screen. In that case, you will notice the gradual but steady revelation of the human condition’s frailty and how it responds to an inevitable, unavoidable end.

The Human Centipede also serves as a nuanced reflection on modern misunderstanding, as naïve American tourists fall victim to this crazy scientist and are treated with a steely, persistent lack of empathy that seems to befit their vulgar, stupid natures.

Similarly, he deliberately positions the Japanese tourist at the head of his monstrous centipede. The only one of the three who can speak speaks only Japanese, a language he does not understand.

Katsuro’s final statement, in which he creates a moment of severe self-reflection and compares the doctor to God, brings the metaphor to a close.

Despite its horrifying sights, The Human Centipede remained a vital cog in the wheel of horror cinema because of a committed audience that accepted the metaphors it depicts.

There were also confirmed true stories of experimentation, which The Human Centipede draws on. This enabled it to climb beyond ignominy and sustain a cult following for decades.

Conclusion

For those wondering, was The Human Centipede real? You now have a better understanding of the inspiration and source of the movie. The movie was based on recollections of World War II Nazi camp survivors subjected to inhumane experiments in concentration camps.

The experiments were not precisely similar to what is depicted in The Human Centipede, but there are many similarities.

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True story behind The Human Centipede - its link to Nazi Germany as director talks new film

The iconic Dutch horror film The Human Centipede by director Tom Six was released in 2009 and produced some rather visible reactions.

The Human Centipede

There were some key inspirations for Six's original horror flick, but some are much more serious than others.

As the film germinated in Six's mind, he took inspiration from real life and abhorrent episodes in recent history.

Six's chief historical inspiration was the Nazi experiments conducted on Concentration Camp prisoners in World War Two, including the diabolical experiments of Dr. Josef Mengele.

The experiments saw prisoners across Europe forced to participate in tests that mostly ended in death, trauma, disfigurement, and permanent disability.

The monsters also conducted bone, muscle, and nerve transplants on prisoners without the use of anesthesia.

There were also tests of new drugs, weapons (such as mustard gas and poisons) and sterilization on prisoners, against their will, which would have long-lasting medical reprecussions.

Finally, Six was also inspired by the previous cinematic offerings from visceral directors David Cronenberg and David Lynch, and also the Dutch iteration of the iconic reality series Big Brother.

The Human Centipede 2 (Full Sequence)

The sequel film took things to an even darker place, with much more graphic scenes and more disparate inspirations.

Six decided to make the plot very meta: it would focus on a fan of the first film who would then conduct his own sadistic experiments and punishments.

The chief inspiration for this decision was Six's fascination with copycat serial killers, who usually start as fans of the original killer.

The term copycat killer was coined after the killings by iconic and mysterious serial killer Jack the Ripper sparked a number of similar murders.

The film Natural Born Killers starring Woody Harrelson is often blamed for sparking copycat killings, after being loosely based on serial killers Charles Starkweather and Caril Ann Fugate.

The Human Centipede 3 (Final Sequence)

The last film saw Six want to return to the theme of the original joke that inspired the film series: punishment.

The film had a much more satirical tone, but this was one of the many aspects of the piece that critics and fans slammed.

Corporal punishment is always a controversial topic, but its pros and cons were dealt with no sympathy here.

We expect Tom Six's next film to be just as provocative.

The Onania club will be released later this year.

Aetna expands access to fertility services, becoming first major insurer to cover IUI

The True Meaning Of The Human Centipede Movies

When Tom Six's horror freakout " The Human Centipede (First Sequence) " was released in 2009, it was met with much disgust and ballyhoo. The poster boasted that the film was "100% medically accurate," something that no movie poster should ever boast.

The premise was wild and gross and repelled prudes while attracting seekers of the extreme. A mad scientist named Dr. Josef Heiter (Dieter Laser) — clearly inspired by Josef Mengele — kidnaps three hapless tourists (Ashlynn Yennie, Ashley C. Williams, and Akihiro Kitamura) and announces his dark plan while they are strapped to gurneys in his basement. Dr. Heiter intends to surgically connect the three people via their alimentary canals. He will connect one person's face to the previous person's anus, and remove tendons in their knees, forcing them to crawl. In so doing, he will create a human centipede. There is no stated reason for his experiment.

Audiences who saw "The Human Centipede" were appropriately grossed out. The film wasn't so much a film as a geek show, made to test the endurance of whoever dared buy a ticket. It was to fall into a camp next to "Faces of Death" or the various Mondo shockumentaries of the 1970s. And while there is a certain grindhouse integrity to making a film that serves entirely as an endurance test — it takes chutzpah to be so deliberately repellent — it would have been nice if "The Human Centipede" also functioned as, y'know, a movie. As it stands, it barely qualifies as cinema.

Full Sequence

When Six followed up his "(First Sequence)" with " The Human Centipede 2 (Full Sequence) " in 2011, he outdid himself in his efforts to be as nauseating as possible. In the world of "(Full Sequence)," the original "Human Centipede" is a mere fictional feature film that, with its twisted premise, seems to have inspired a mentally ill recluse name Martin (the gloriously off-putting Laurence R. Harvey) into making a human centipede of his own. Not to be outdone by the three-person centipede of Dr. Heiter, however, Martin kidnaps twelve people — including Ashlynn Yennie, playing herself — and assembles them in a filthy warehouse using scissors, duct tape, twine, and injected laxatives. His process is filmed in gruesome detail. The film features forced tooth removal, and a scene with a pregnant woman that should remain tactfully undescribed.

"(Full Sequence)" is one of the most revolting films available to the public, and that is not meant affectionately. It sought to be repellent, and boy howdy, is it ever. There is no longer a pretense that the "Human Centipede" series was meant to function as traditional films. These are only meant to function as dares, as tests of how far out of the lines Six would allow himself to color. If a viewer has remained incurious, one can hardly blame them.

But with "(Full Sequence)" a curious commentary began to emerge. There is a metanarrative at work here. After all "The Human Centipede" is only a movie in the sequel.

The Anxiety of Influence

At first glance, the metanarrative points to director Six bragging about the success — and the disgust — born of his 2009 film. Like a kid eating a second bug, he is childishly proud of the fact that his first bug-eating caused other kids to barf. The metanarrative could easily be construed as a form of adolescent vanity.

But Six, perhaps unintentionally, has made a comment on the way we consume media. Like a dark mirror to Jean-Luc Godard's "Breathless," "(Full Sequence)" stars a character who takes his behavior cues from the art of others. Influenced by what he sees on a screen, both Martin and Godard's Jean-Paul Belmondo aim to construct a new kind of living art wherein they themselves are real-life movie characters. Belmondo takes his behavioral cues from "cool" icons like Humphrey Bogart, and fashionably sports fedoras and cigarettes. Martin takes his cues from "The Human Centipede," and unfashionably kidnaps innocents and connects their faces to others' bottoms.

Six, now several generations removed from "Breathless," seems to be skewering the very idea of cinematic influence. Audiences and filmmakers who take their cues from earlier films are now merely victims of cynical filmmakers who have nothing interesting to say. One may be charmed by the Hitchcock light of Brian De Palma, for instance, but to Six's eyes, that's no different from having your face strapped to another person and being forcefed their, uh, product.

Final Sequence

One might bristle at the notion that all influence is a negative thing. After all, every piece of art stands as a criticism, a commentary on the art that came before it. Literary critic Harold Bloom referred to this as the Anxiety of Influence. Six seems to be criticizing something far more specific. He is targeting a media landscape full of reboots, regurgitations, and re-visitation. Younger generations are constantly being dictated to. Hey, kids. You know what we liked? "Ghostbusters." Here's a brand new " Ghostbusters " that is 100% for us and not for you, but you better consume it anyway. We're recycling every idea and every visual cue, and we're exploiting the image of a dead actor. Enjoy!

Tom Six merely applied a revolting metaphor. An extreme political cartoon. Oh God, is "The Human Centipede 2" ... important?

And, just as "Star Wars" once came to influence actual American war activities — Ronald Reagan's fantastical spacebound Strategic Defense Initiative was nicknamed "Star Wars" — so too would "The Human Centipede" come to inform American institutions.

The most revolting of the series, "The Human Centipede 3 (Final Sequence)" pulled back another layer of reality, and saw Dieter Laser and Laurence R. Harvey playing prison wardens in a universe where the first two films are both but films. The characters in "(Final Sequence)" are monsters. They torture and mutilate the prisoners in their care, all under a waving star-spangled banner.

The Human Centipede as American policy

And some of the thing the Laser character eats ... Well, just consider this a dire warning against actually watching the film. Its tastelessness will be difficult to consume, even for the most jaded among us. " The Human Centipede 3 " is, without exaggeration, one of the most nauseating films a human can experience.

In it, not only are the first two "Centipede" sequences films; director Tom Six also appears in the film as himself. To quell the rowdiness of a tortured prison population — at George H.W. Bush State Prison — Bill Boss (Laser) and Dwight Butler (Harvey) conceive the idea to make all the inmates into a massively long, hundred-person human centipede. The film details how many people would be required to make such an endeavor happen. A single psychopath cannot make a centipede of that size. Now, large groups of people must be convinced to participate. And, to do so, an argument must be made to its necessity.

No longer a media commentary, Six has — quite bluntly — taken aim at the grossness of the American prison system. The centipede can be seen as generations of unduly incarcerated American prisoners are force-fed American "ideals," all in the name of being reformed. The American criminal justice system, Six is saying, is an excuse for generational institutionalized madness to play itself out. The film ends with Bill Boss, shirtless and covered in blood, firing a gun into the air, wailing in insane glee as his hundred-person centipede languishes below.

The "Human Centipede" movies are too disgusting to enjoy, and any intellectual seeker will certainly be scared away by how aggressively contemptible they are. But Six, for all his adolescent shock impulses, had something to say.

It was gross, but he said it.

The Story Behind The Human Centipede

A new breed of body horror

“I saw a child molester on television and I said, ‘They should stitch this guy with his mouth to the ass of a very fat truck driver. It would be a really good punishment for him.’ Then I thought, ‘That’s a cool idea for a film.’”

Director Tom Six there, explaining the origin of his new, demented body horror flick The Human Centipede (First Sequence) .

Taking that dark, off-the-cuff joke, Six – whose previous credits include little-known films Gay and Honeyz - decided to apply it to an icky, squirm-inducing horror movie.

The premise? Three backpackers in Europe are royally stitched up by a nutso surgeon who wants to create – yup – his very own human creepy crawly.

It could be the most shocking body horror to come out this side of Martyrs and Antichrist , with its ‘David Cronenberg on acid’ trappings. As one US critic noted, it’s the film “that you can’t unsee”.

Here’s how it got made…

Next: The Origins [page-break]

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The Origins

So you have a sinisterly brilliant idea for a horror flick. The concept’s so queasy and unnerving that it both repulses and intrigues. And you’re filled with unbridled enthusiasm for the project. But how the heck do you get the thing financed?!

Writer-director Tom Six decided the stealth, softly-softly approach would be the best tactic…

“We made films in Holland before and so we had a group of investors,” he explains. “We told them we wanted to make an international horror film and we were going to stitch people together.

“We left out the words ‘mouth-to-ass’ because we knew they wouldn’t fund it. If I had mentioned ‘ass-to-mouth’, I think they would have said, ‘Have a nice day, bye!’ But they have seen the film and they loved it. So the trick worked very well, fortunately.”

And you can understand his reservations. The story of two American girls who are kidnapped alongside a Japanese man by demented retired surgeon Dr Heiter - and then have their mouths sewn to each others’ unmentionables in a terrifying experiment – would keep just about any investor clutching onto his or her cash.

But Six’s thought-out concept no doubt helped assuage their concerns post-shoot. Instead of aiming to fashion a quick fix shocker that induced aisle vomiting but little else besides, Six wanted to establish a psychology behind the model.

Naturally, his biggest inspiration was the work of David Cronenberg, alongside the boundary-pushing scarefests that are a hallmark of Japanese filmmaking.

But it was the inclusion of a German villain – the menacing Dr Heiter (Dieter Laser) – that hinted at a brain behind the project. Six drew on the Nazi medical experiments that took place during World War II as a very real launch pad for his ooky idea.

Further still, the Japanese male lead – Katuso (Akihiro Kitamura) - played on the War-time notions of divided nationalities, and created a language barrier between the antagonist and his prey.

Next: The Human Guys [page-break]

The Human Guys

“A week after we talked,” notes Dieter Laser of his initial meeting with Six, “I suddenly got small and afraid. But then I got the script and I discovered, ‘Oh boy, there’s so much possibility!’”

Signing on to play sinister surgeon Dr Heiter, Laser – a veteran of German cinema – agreed to a role that was bound to illicit outrage from audience members. But Laser, like the financiers, could see what Six was trying to do.

“The [ plot ] is a good marketing thing that will create discussions and anxiousness and everything. Under the surface I discovered why he chose a German. I regard the film as a grotesque [ parody ] about the Nazi psyche.”

Notes Akihiro Kitamura, who plays victim Katsuro: “I’m the lucky guy. I don’t really mind having my face attached to a female’s butt. I don’t mind.”

Still, he admits that “Dieter’s a pretty scary guy. I thought, yo man, that’s going to be awesome to have some hot chick attached to my ass. But because it’s a horror film setting, it was kind of a scary feeling, actually.”

“For me there was only one actor who could play the role of Dr. Heiter,” says Six. “I saw a couple of DVDs where Dieter Laser was playing and I think he's absolutely a brilliant actor. So we flew to Berlin to meet him and we were very excited about what he would think about my story.

“And I told him in detail and he absolutely loved the idea because he's just as crazy as I am and in a couple of hours we had a deal and he was the one.”

Next: The Human Girls [page-break]

The Human Girls

For the parts of the two female American tourists who are conjoined with Katsuro, Ashley C Williams and Ashlynn Yennie were cast as Lindsay and Jenny.

“The two American actresses were really hard,” Six notes. “I wanted very beautiful and very intelligent and very good actresses, of course...

“We were casting in New York and I made some drawings of the human centipede and a lot of actresses thought I was crazy and didn’t want to work with me.

"A lot of actresses only want to be beautiful and I had to ask those actresses to be mutilated. So they left. But the wonderful Ashley and Ashlynn, they had the balls to play it.”

The Human Centipede (First Sequence) marks Williams’ first lead role in a feature film, the 26-year-old having previously only appeared as a Nelwyn villager in fantasy Willow .

“I met Tom at my first audition for the film,” Williams says. “He wanted to show me a sketch of what the human centipede would look like. Before he showed it to me, I will never forget, he said, ‘Are you easily shocked?’ and I said, ‘Nope!’ So then he showed me the sketch.

“I wasn’t shocked at first but I had never seen anything like that before, I was like. ‘This guy is crazy,’ but he was so sweet and passionate about the story that I became intrigued about the film, and about this crazy man behind the project.”

Yennie is also a film newbie, having only appeared in TV movie Evan And Gareth Are Trying To Get Laid.

“I love the fact that Tom’s work is being compared to Cronenberg’s work,” the actress notes.

“It is very true with this film, beauty is destroyed, human fear is exposed and there is a little infection mixed in. All very close to the genre that Cronenberg has made his own.”

Next: The Centipede [page-break]

The Centipede

“I wanted a real operation report,” reveals Six of his diabolical design for a human centipede. “So I went to a Dutch surgeon. He said, ‘No, no, that’s against my medical oath.’

“But he’s a movie lover, so after a while he made a very detailed operation report. A surgeon could actually make in a hospital a human centipede. That’s what fascinates me. And makes audiences feel more horrified by the idea.”

Like all the best horror films, The Human Centipede (First Sequence) only ever hints at its explicit content, and contains very literal actual exploitative footage. The use of bandages proved pivotal in ths respect, allowing Six to hint at the atrocities that were going on underneath.

Using sketches made by the Dutch surgeon whom Six visited, the special effects team – led by father-son duo Rob and Erik Hillenbrink – designed hard underwear for the actors to wear in order to imply the mouth-to-bum connection.

“We had to wear this special underwear, like a diaper... a hard diaper,” says Kitamura. “And where my ass is there’s this rubber thing for the actress to bite onto it. When we were trying that in the beginning, they were feeling it a little bit. But they are good actors.

“They liked the experience. It’s good it’s scary. It’s good it’s humiliating. Because they can be great actresses.

"We got a massage every two or three nights. You know the scene where we climb up the stairs? There was no stunt double. It’s really tough on the neck and back. If we complained, they listened to it.”

Jokes Williams: “We made a very nice centipede! When we all met up together for the first time we were like, ‘Hello, nice to meet you, I’m going to be attached to your butt soon!’”

Still, the actress adds that it was an uncomfortable shoot – especially for herself, being the middle ‘segment’ of the centipede.

“I know all of us had some difficulties being part of the centipede,” she says. “But I feel that being in the middle was very hard because I had Ashlynn tugging at me with her mouth in one direction and Aki pulling me forward in another. So we all had to coordinate.

“It put lots of pressure on my jaw when the Centipede would walk and also climb up those stairs. We were all regretting doing that scene. It was the hardest thing the Centipede had to do, because we were really doing it. No help from the crew!”

Next: The Release [page-break]

The Release

So far, The Human Centipede (First Sequence) has taken numerous film festivals by storm, having premiered at the London FrightFest, Lees International and Screamfest circuits.

Tom Six noted that thanks to the high amount of word of mouth, numerous studios approached him with offers to distribute the film.

In the end, IFC Films snapped up the rights for distribution in the USA and Canada, and The Human Centipede was given a limited release in the States on 30 April.

“ The Human Centipede is more artfully done than you think,” says Williams. “Its horrifying but also medically accurate, intelligent and not a slasher movie! There are a lot of fans out there who have seen it that said ‘This is the grossest, craziest movie I have ever seen’, at the same time they give it 5 out of 5 stars.”

Reviews have been mixed. “ The Human Centipede is not what it's cracked up to be,” we reported last August from FrightFest 2009. “it is not, actually, nearly as vomit-inducing and the hype suggests. Far from being this year's Irreversible , Martyrs or Inside , films that push boundaries, it is (relatively speaking) a rather tame affair.”

Still, others have lapped it up, with Entertainment Weekly favourably reviewing the film and saying that Six "has put together his nightmare yarn with Cronenbergian care and precision”.

The flick has also received a fair few awards, having taken home Best Picture prizes from Fantastic Fest, ScreamFest, Sainte Maxime and Ravenna Nightmare Film Festivals.

Roger Ebert perhaps surmised the film’s divisive nature best: “I am required to award stars to movies I review. This time, I refuse to do it. The star rating system is unsuited to this film. Is the movie good? Is it bad? Does it matter? It is what it is and occupies a world where the stars don't shine.”

Next: The Human Centipede II (Full Sequence) [page-break]

The Human Centipede II (Full Sequence)

Ah yes, you perhaps noticed that The Human Centipede is followed by some sneaky bracketed words – (First Sequence) giving us a less-than-subtle hint that this could be just the start of a, ahem, string of centipede horror pieces.

You’d be right in assuming that. The flick has yet to receive a worldwide release (it’s not even got a fixed UK date yet), but a sequel entitled The Human Centipede II (Full Sequence) is now in the works with Six at the helm.

“I had so many ideas, which I couldn’t use in this part,” the director reveals. “I wanted, first, people to get used to this idea. Now I can expand my ideas and hopefully create something really original. I want to offer people some more!”

So will a sequel extend the concept and take the ‘bigger, faster, stronger’ sequel route by adding more humans to the centipede segments?

Six is up to the challenge. “It's very challenging for a film maker to make a sequel,” he says, “because a lot of sequels are very disappointing for fans and for audiences. So I really wanted to have a really original idea to make a sequel and I think I have something that people won't expect.

“In part two I can use all of my imagination and put everything in part two. I can't tell you what it's about of course because I want to keep it original and a surprise to audiences but I hope I will succeed. I'm going to shoot it in June in London and hopefully it'll be ready by the end of the year.”

Not that Six is planning on stopping at centipedes. Now he’s gotten the industry’s attention, he’s planning on making more films.

“I really want to explore the horror genre combined with drama some more,” he says. “So I'm writing a script right now for a new film after the centipede that's going to be completely different but a film that will definitely push a lot of boundaries.

“Hopefully again it's very original and something that hasn't been done before and I'd like to shoot that in LA next year.”

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The True Stories Behind the Human Centipede – The Most Misunderstood Horror Film?

If you ask around about the most horrific films ever made, a lot of people would talk about The Human Centipede – a trilogy of films that have always been perceived as twisted, depraved, and horrible by most casual horror buffs.

However, in the mind of the true horror aficionado, The Human Centipede represents a true opus – a layered narrative that is widely misunderstood, specifically due to superficial interpretations.

In truth, a little dive into the backstory and metaphor layers of The Human Centipede can reveal why viewers need to look beyond the outward horror and really embrace the inner message of the film to grasp its reality. If you have been fascinated by this film and want to learn more about it to develop a more nuanced understanding of it, here is The Human Centipede explained.

Table of Contents

The Human Centipede Explained

Coming from Dutch writer-director Tom Six, The Human Centipede was to attempt a radical redesign of the stale, tired horror genre of the time. The drive to do something radical is partly what made the movie so controversial in the end.

In the movie, a “mad scientist” kidnaps three tourists. He then proceeds to torture them in a variety of ways, finally surgically joining them anus-to-mouth to form a grotesque conjoined triplet, the titular Human Centipede. Needless to say, the film provoked horrified reactions from a major part of the global audience, was panned by many critics, and remains banned in several areas.

The film was initially refused a certification and remains, to this day, a body horror cult classic a la David Cronenberg.

Diving into Metaphors and True Stories Behind the Experiments

At the heart of The Human Centipede are various metaphors that rise from the visuals and lend new context and nuance to the premise. The most obvious of these is the parallels with Nazi Germany and the true stories coming from that time in history . During the Nazi rule, there were abounding rumors of German scientists trying to perform gross experiments on humans . Of special note were the experimental pursuits of notorious scientist, Dr. Josef Mengele . These were the sort-of true stories of Human Centipede-like experiments.

These experiments put a gruesome crown on a time that was already abhorrent to the global populace. A lot of the tests resulted in injury, disability, trauma, and death for the unfortunate and unwilling participants. Some experiments were carried out on twins, who were forcibly sewn together to replicate conjoined twins who share a similar fate. Other experiments involving experimental transplants and grafts of bones, skin, muscles, and nerve, usually carried out without any anesthesia.

Scientists would also try out new biological weapons and drugs on their unfortunate victims without consent. New surgical procedures of brain surgery and sterilization were also tried out with aplomb, often with resulting death, or, far worse, long-term medical repercussions. The lead character, the scientists carrying out these experiments, is also aptly named Dr. Josef Heiter to drive the metaphor home. The Human Centipede is clearly alluding to these true stories of horrific experimentation.

Nazi physician Carl Clauberg (left) performing medical experiments.

Cinematic Choices

The Human Centipede , while lacking any element of subtlety in the vein of Wes Craven movies or The Wicker Man , nevertheless makes it very clear that there are historical parallels embedded in the visual narrative that deserve a closer look.

There is an inherent attempt to acquaint viewers with the finality of situations that end up in a loss of self-respect, comfort, and life. The feeling of impending doom has different impacts on different victims, and their reactions tell fascinating stories about who they are as people.

The lack of subtlety and the deep dive into blatant sensationalism serves to prop up this metaphor to a great degree. Six almost dares the audience to look away, and many of them would. However, keep your eyes peeled on the screen and you would be able to see the slow but sure exposure of the vulnerability of the human condition and how it reacts to a certain, inevitable end.

The Human Centipede also resounds as a nuanced commentary on modern miscommunication , as the American tourists unwittingly fall victim to this mad scientist and are greeted with a steely, determined lack of communication that seems to befit their crass, ignorant natures.

Similarly, he makes a conscious decision to place the Japanese tourist at the head of his grotesque centipede. The only one of the three capable of speech can speak only Japanese, a language that he himself does not understand.

Katsuro’s final speech provides a conclusion to the metaphor, when he creates a period of brutal self-reflection and likens the doctor to God.

Key Takeaways of The Human Centipede

With all its horrific visuals notwithstanding, The Human Centipede remains an important cog in the wheel of horror cinema due to a dedicated audience that embraced the metaphors it portrays. And there were real, true stories of experimentation that The Human Centipede is clearly playing off of.

This helped it rise and keep its head above ignominy and maintain a cult following for decades. Director Tom Six also departed from this formula to make very different sequels, each with their own brand of metaphor, storytelling, and even more stark, revolting visuals to further drive the point home.

— FOUNDATIONS OF HORROR —

Additional Reading

Grotesque Realism and the Carnivalesque in Tom Six’s The Human Centipede (First Sequence) and The Human Centipede II (Full Sequence) [PDF]

The Monstrous Metallic in Medicine and Horror Cinema

No Pain, No Gain: Strategic Repulsion and The Human Centipede

Last Updated on February 23, 2023.

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The Human Centipede (First Sequence)

There’s a certain breed of horror-film junkie who craves the extreme (I know, I’m one of them), and the dosage of awesome ickiness has to keep getting upped. It’s to my fellow depravity-heads — and to no one else — that I recommend The Human Centipede (First Sequence) , a surgical-nightmare exploitation film that has no pretense to anything beyond making you go, ”My God, now that is gross.”

In Germany, a stalled car strands two tourists (Ashley C. Williams and Ashlynn Yennie), who take refuge in the woodsy home of a local resident. His name is Dr. Heiter (Dieter Laser), and he’s a celebrity surgeon and secret psychopath who drugs the women and straps them into beds in his basement laboratory, where another victim already lies. He then explains that he plans to make all three of them part of a mad experiment in which he will surgically join them, mouth to rear end, to create a human centipede. Much of the film’s ”entertainment value” rests on the sadistically outlandish performance of Dieter Laser, who’s like Boris Karloff starring in a movie by Rainer Werner Fassbinder. The film itself, as staged by Dutch director Tom Six, is a fairly crafty piece of over-the-top suspense. By showing exactly what it promises to show, it lets us peer into a B-movie abyss. But unlike its obvious influence, the 1999 Japanese shocker Audition , The Human Centipede has no real-world echoes. It’s an only-in-the-movies sick goof. B+

See all of this week’s reviews

[Interview] Tom Six Reflects On 10 Years of ‘The Human Centipede’ and Teases Future ‘Centipede’ Projects

It is surreal that the first Human Centipede is celebrating its 10th anniversary this year. I vividly remember hearing about the film for the first time back in 2009, talking with friends about its brutal new take on body horror. When we finally saw the film, we couldn’t get over the grossness of it all; from shock chuckles to our churning stomachs, the Human Centipede made for an experience that engaged with all our senses.

Since its release, the film has become a gem of pop culture; from numerous parodies and tributes, Human Centipede became a game changer in the world of body horror. While we’d become used to shocking films for years beforehand, the Human Centipede established a sincerely uncomfortable atmosphere, offering intense, unnerving horror.

In honor of the film’s anniversary, I had the chance to interview Human Centipede ’s writer/director Tom Six , asking about the film’s impact and his feelings regarding its creative process.

Michael Pementel: Over the years, how has it felt seeing fans and critics react to the Human Centipede ?

Tom Six: “When you make a film trilogy that really has spread over the whole world like an aggressive virus, having almost the whole youth world population at least know about them, [that] makes little Tom proudly stand erect and salute. When your films become pop culture and [you] see all the famous references, strong audience reactions, great film critics and crying film critics, tattoos, spoofs, celebrity fans, etc. – [that] is the ultimate indie filmmaker’s dream!”

MP: How did you think people would react to the first film? Were reactions different than what you expected?

TS: “When I was writing the first pede [sic] I already knew I had something “special.” But when I was shooting the first pede ’s “feed her!” scene, lightning struck, and I knew I had something “spectacular.” And what I thought would happen thankfully happened: people loved it or hated it. There was nothing in between. Like all art should be. Funny [thing] is, there are a lot of people that absolutely didn’t believe in the pedes ; financiers, actors, companies, film crew, distributors, etc. heavily detested the idea. Now they all are crying in their little beds.”

MP: Considering your filmmaking inspirations – How did you want Human Centipede to push the boundaries of “shock” cinema?

TS: “I am all about creating original work and pushing boundaries of art/film. I hate mediocre shit. It’s great to have raised the bar but not just to shock for the shock. I’m the guy that travels the seven seas while others stay safely on shore. And I salute the very few fellow filmmakers who have and do the same because I know how hard it is, especially now in our politically correct times.”

MP: During the production of Human Centipede and upon its release – Did you ever imagine the film to have such a cultural impact on cinema and horror?

TS: “Like I said, I always knew I had something “special,” something that would make a massive impact. I love to light up a cigar and say: ‘I love it when a plan comes together…’ and I’m very grateful for all the loyal fans, haters, and partners in crime that believed in it that made it so huge.”

MP: Looking back on the creation of Human Centipede – What was the most rewarding part of the filmmaking? If there is anything you would change, what would it be? Or why wouldn’t you change anything?

TS: “I would absolutely not change a single frame! My writing and filming were totally free of any self-censorship. Even when I knew turning the whole thing into a reality would become extremely difficult and challenging because making this kind of cinema is no walk in the park. The biggest reward is being a little independent filmmaker from, of all places, Holland, totally doing everything with Ilona (my sister and partner in crime) ourselves; and that the whole world and generations to come knows about your films and who you are.”

MP: After these ten years since the film’s debut – How would you sum up your feelings regarding the film and your experience since as an artist?

TS: “These films are my brain-babies and I am a very proud daddy. With the movies, all my depraved dreams came true, and now I have many more original and depraved film scripts in the works. The world has not seen the last of this humble filmdictator [sic].”

MP: Is there anything else we can look forward to in the future regarding Human Centipede ?

TS: “This year we will release a graphic novel of the first Human Centipede to celebrate its 10th anniversary. I also have a Human Caterpillar script I’m working on (see the death row prisoners in Pede three). And in a way or form, the Human Centipede concept might come back in some of my future films.”

Michael Pementel is a pop culture critic at Bloody Disgusting, primarily covering video games and anime. He writes about music for other publications, and is the creator of Bloody Disgusting's "Anime Horrors" column.

‘The Deliverance’ – Andra Day and Glenn Close Talk Fear, Cycles of Abuse and the Unique Filming Experience [Interview]

Netflix’s possession horror movie The Deliverance centers on a single mother struggling to raise her kids while struggling with her inner demons, and that’s before the actual evil takes root in the new family home. Cycles of abuse lead to intense confrontations in this family, particularly between protagonist Ebony Jackson ( Andra Day ) and her mother Alberta ( Glenn Close ).

The Deliverance , out now in select theaters before arriving on Netflix August 30 , is loosely based on a true story: that of Latoya Ammons and her 2011 haunting in the house that’s also known as the Demon House . While director Lee Daniels ( Precious, The Butler ), who also wrote with writers David Coggeshall and Elijah Bynum , spends a lot of time establishing complex characters that stand apart from their real-life inspirations, the filmmaker previously told us in a recent interview that he wanted to really dig into the drama and get to know the characters first before pulling the rug out from under viewers with the horror.

Daniels also explained how Glenn Close’s character doesn’t have a real-life counterpart; Alberta is a wholly original character created for this story. Alberta is a deeply complex character, grappling with her own place in Ebony’s cycle of abuse, which leads to no shortage of explosive exchanges between mother and daughter. Tha t The Deliverance really delves into this relationship means Andra Day and Glenn Close share a lot of intense scenes together, and their director afforded them the rare gift of ample rehearsal time to sink into their roles.

“Lee gave us that,” Close says of building that mother-daughter relationship with Day. “It was generous to give us that time, usually you don’t get that much time. I think we came to understand that these are two women who exist in this cycle of abuse. The movie, I think, then becomes almost a metaphor for breaking that cycle and the power and the courage that it takes to break it. You can translate that into so many different stories. But I think where there’s great tension, there’s also potentially great love.”

Behind the scenes of The Deliverance with Lee Daniels

As for Day, she recounts how inspired she felt to work alongside not just Close but the entire cast. “I mean, it’s impossible not to learn more about your craft when you are on set with Glenn Close, when you are on set with Mo’Nique, with Anjanue Ellis, with Caleb [McLaughlin], Demi [Singleton] and [Anthony B. Jenkins],” Day gushes. “Again, these are all not just veteran actors, but these are legendary iconic performances that they have given time and again. One of the things that I learned, particularly from Glenn, is that there was zero ego on set. They deserve to have that. You know what I mean? When she walked on set every day because it was a new character, she approached every day as if it was almost her first day on set, trying to get this right and really wanting to do this well. When you see somebody who you admire so much, and you’re a fan of their work, for them to have the same hunger and almost the same, not necessarily fear, but that drive underneath, you go, oh, that’s what has kept her and what has made her so amazing and so iconic. All of them, you know what I mean?

“That is what I learned: to stay that way, keep it fresh and exciting and keep that sort of hunger in your belly. Once you lose that, you should probably let it go. “

Alberta may be a complex woman, but The Deliverance is Ebony Jackson’s story, and Andra Day’s character gets put through the emotional wringer as life throws every high-stakes obstacle her way with few allies to help. She’s also a character with a dark past that’s relayed piecemeal, revealing new facets late into the film. When asked at what point Andra Day felt like she fully understood who Ebony Jackson was, she revealed a surprising connection with her character. The actor even researched Latoya Ammons.

“Through multiple conversations,” Day said of finding her character. “As Glenn said, we did have ample time to prepare, and I actually knew about it on the set of The United States vs. Billie Holiday . So, it wasn’t until the end of filming Billie that he first brought it up to me. I was studying the woman. I was studying her family. But it was really through my conversations with Lee. I think the commonality, I have had a lot of fear in my life. Fear of not just failure, fear of just not being liked, not being accepted. Fear. Fear of showing up to every interview, to every set, to every show, to every, because I just am not good enough. I was reminded through her character that perfect love casts out fear.

“That was a theme for me through this project. Understanding who she was when she was sort of coming to her own understanding of faith. She was almost forced. It was like she had to be forced into this position in order to receive that and transform. I often find myself in that position. So, I think really understanding her came to finding those commonalities, which is like, it’s really, really hard for me to sort of change or receive different things or do different things unless I’m at this critical point, or unless I’m at critical mass and I have to. I think we have that in common, but once we do, then we are changed and we are transformed. We see that in Ebony. That’s what helped me to understand her.”

The Deliverance gives a new spiritual angle to possession horror, one that Lee Daniels wasn’t taking any chances with as he invited an apostle to set every day to anoint with prayer. It may have been an unconventional fixture on set, but it lent a calming presence and made the cast feel protected.

The tenured Close remarks, “I’ve never seen that on a set. I’ve never witnessed this on a set. Never had somebody talking tongues before you start working. I loved it. I loved every single minute of it, every minute of it. I think it really did inform each day when he was there, and we did that. I felt protected.”

“Yeah, that’s exactly it, “ Day agrees.” That’s what I was going to say too . As she just said, I felt protected. I felt covered. I think we all did. Whether you engaged, not everybody had to engage with him if they wanted to or if they didn’t want to. But he’s done this. He has performed many deliverances here, in other countries, and in a lot of different places. He’s very familiar with the process, how it’s supposed to go, and the spirit from which it’s supposed to come if you are representing it from this perspective. So, I loved Apostle Louis. I loved praying with him and working with him on set. And it just reminded me that we’re here for a reason. We’re here for a purpose. And it’s not just to scare people. For me, I want people to encounter God. For people to encounter light. That was what that was for me. “

“ It was great, “ Close adds. “Lee would say, okay, everyone, we’re going to pray now. Come if you want to; it’s okay if you don’t want to.”

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OMNI LOOP: TRAILER 1

Alien: romulus: a love letter to the alien franchise, with mixed results, woman of the hour trailer 1, the becomers: what’s weirder, aliens or 2020, kraven the hunter: trailer 1, saturday night trailer 1, this is no game: why ready or not still matters, rebel ridge trailer 1, alien: romulus: not quite stellar, his three daughters trailer 1, popcorn frights 2024: lizzie lazarus, strange darling trailer 1, anatomy of a gimmick: the human centipede, “the most horrific film ever made”.

Anatomy of a Gimmick: The Human Centipede,

The Human Centipede trilogy is arguably one of the most infamous horror films of recent decades, spawning a cult fandom of midnight moviegoers and a ubiquitous wave of revulsion from everyone else. The premise is most likely common knowledge to horror fans, anyone who went to middle school in the 2000s, or viewers of South Park among others–– it’s become something of an urban legend. It’s simple: a human centipede is three or more people sewn together mouth to anus in a line with the goal of creating one long, fully functional gastrointestinal tract. Who does the connecting, how many people are connected, and the reasoning behind why anyone would want to do this in the first place varies by film, but none of that matters, really–– the premise itself is what people pay to see, encouraged in large part by a prodigious word of mouth campaign begun by the film’s director.

Horrific, Infamous, or Both?

Even with the awareness that the film is a deliberate provocation made by a filmmaker who decries “political correctness” in just about every interview, Ebert couldn’t resist feeding into the hype, calling it “depraved and disgusting” and refusing to give the film a star rating at all, a move he typically reserved for pornography (i.e. Deep Throat ) and rape-revenge films ( I Spit on Your Grave ).

That being said, while many people over the past 13 years since the first film’s release have called The Human Centipede trilogy something along the lines of “the most horrific film ever made,” it was actually the film’s marketing campaign that said it first. The month the film was released, David Cox , writing for The Guardian, worked to track down the quote . When asked, director Tom Six claimed it was from The Sun , which proved to be false.

Alongside this sensationalist marketing tactic, another claim, this one more dramatic and completely absurd, is emblazoned on every poster: the film’s tagline insists to the reader that The Human Centipede is “100% medically accurate.”

Like other horror filmmakers before him, Six’s approach to the franchise reads as one long, money-making marketing gimmick that incidentally created a film trilogy–– and that’s the point. Deadpan style aside, the movies themselves are self-referential curiosities designed to maintain a perpetual hype machine of the sort that kept stars like Vincent Price in expensive Dracula capes for decades.

This strategy allowed Six to create something infamous off the back of a first film that–– and maybe as a horror fan I’m biased–– simply doesn’t merit the hype he himself gave it. Ultimately, though, the very fact that such an infamous franchise was built off of an elaborate, self-perpetuating gimmick and not the films’ gross-out premise, makes the Human Centipede trilogy worthy of the “splatter” moniker coined for films that were doing the exact same thing more than half a century ago.

Let’s get down to brass tax here: is The Human Centipede really that disgusting? When it comes to the first film in the trilogy, it’s a matter of taste and tolerance. All three films do indeed feature coprophagia, bodily fluids, and what the MPAA would call “graphic nudity” among other more or less depraved things. They’re stories about perverted men doing perverted things to other people, many of whom are also perverts. The first film though, is also interestingly antiseptic in the era of “torture porn” films like Saw (2004) and Hostel (2005) set in ubiquitously dingy basements full of flickering lights and rusty knives, needles, sheers, and all number of other tools of torment.

Filmed in Holland, The Human Centipede: First Sequence is set in the sterile, modern home of a crazed surgeon, Doctor Josef Heiter ( Dieter Laser ), whose Nazi-inspired human experiments take place in a clean, well-organized surgical theater with little on-screen blood or guts.

The centipede itself is also unexpectedly well-kempt. It consists of two American women and one Japanese man (in what Six claims is a World War II allegory, though as a metaphor it’s decidedly mixed–– why does the Josef Mengele stand-in German doctor incorporate a Japanese man into the centipede if Japan and Germany were allies? Where are the French, British, or Italians? But I digress). While the midnight moviegoer/gore-head might expect to see some anus-to-mouth contact in a film about exactly that, each victim’s face is wrapped in clean, white gauze so thoroughly that only their petrified eyes remain visible.

They crawl around moaning and protesting their own existence without doing much else for the last 40 minutes of a 90-minute movie, only giving in to what I’ll describe as nature’s call once in a set piece that relies on the implication of what’s going on under those layers of unstained linen for its shock value. Though this may sound ironic, while the strategy of eliding direct, dramatic moments for psychological impact is well-used in classier horror films from Val Lewton ‘s 1940s classic, Cat People, to Spielberg ‘s Jaws , for a film selling itself with human feces, this tactic seems, well, cheap.

While the first film isn’t particularly gory for all its grotesquerie, the marketing campaign and the infamy it spawned has an incredible amount of historical precedence in the genre. In 1963, Herschell Gordon Lewis ‘ first horror film, Blood Feast , was banned from traditional cinemas for its cannibalistic subject matter and gore made of real animal entrails. It ran at drive-in movie theaters to great financial success. This film, and the countless dozens he made subsequently, earned him the name the “Godfather of Gore” and created what became known as the “gore”–– or “splatter” subgenre as George Romero called it–– of horror films.

That said, the film’s success was due less to its premise and more to the word of mouth generated by the marketing tactics Lewis used. In the 1950s, Lewis began his career in advertising, later graduating to that classic money-making genre, softcore pornography (or, “nudie-cuties” with titles like Boin-n-g! and Goldilocks and the Three Bares ).

With Blood Feast , Lewis and his crew engaged in a series of stunts similar to Six ‘s fabricated quote from The Sun, providing viewers with vomit-bags upon entry and filing lawsuits for indecency against their own film. The tagline on the film’s poster read: “Nothing so appalling in the annals of horror!” Sound familiar?

Earlier horror films by infamous exploitation director and producer William Castle, known as “the master of gimmicks” or “the abominable showman,” included similar tactics, for example hiring a woman to faint mid-screening of his 1959 film The Tingler , or insuring the audience members in case of death from fright for his film Macabre in 1958.

In the 1990s, these types of campaigns came back to the fore with films like The Blair Witch Project (1999). This found footage horror classic employed assurances of veracity to market itself to large audiences on a small budget. Missing person posters of the characters in the film were put up as part of a stunt to convince viewers the film depicted the real demise of its cast. During early screenings, the promotional team would pass out flyers encouraging audiences to come forward to the police with any information they may have about the case, and, most famously, their website included “real” clips of police and investigators discussing the case, making it one of the most viewed websites of its time.

The Human Centipede trilogy, then, was conceived in a fertile moment for horror film gimmickry and exists in a long line of low-budget horror films, many of which claim to be the most horrific films of all time. The sequels work harder still to perpetuate the gimmicks and strategies laid out by the first film’s marketing as they carry out their twisted premise.

“100% Medically Accurate”

The Human Centipede 2 (Full Sequence) (2011) is, indeed, that gross, but it’s also designed to continue building up the legend of the first film. Tom Six asserts that each film within the trilogy is one segment in a film centipede because each film leaves off right where the next begins. This move allows Six to begin each movie with a breaking of the fourth wall, showing the last film’s final moments and credits, reorienting the viewer not towards the story of The Human Centipede , but to the films themselves, each of which is a fiction film in the diegesis of its successors.

The second film follows a nonverbal, Human-Centipede- obsessed fan, Martin ( Laurence R. Harvey ), through his tragic and repellant life defined by conflicts with his abusive mother (and everyone else). Driven by his goal to see if Six ‘s claim that the first film in the trilogy is indeed “100% medically accurate,” he clumsily kidnaps people at gunpoint and attempts the centipede surgery with duct tape, his mother’s kitchenware, and zero medical expertise. Rape, infanticide, murder, and human-centipeding abound, likely meeting the expectations of the most avowed gore-heads. His mother and psychologist both abhor his love of the first film–– serving as a mouthpiece for negative critical reception.

In terms of motivation, Freudian nods and winks from phallic cigars to Oedipus complexes hardly attempt to elide the fact that the character’s central motive for building a Human Centipede is just the perverted draw of the last movie. He keeps a scrapbook with clippings from the first film under his bed (100% medically accurate” emblazoned across the first page) and kidnaps the actors from the first film (playing themselves and talking up how scary and, again, 100% medically accurate the film is) to add to his own centipede.

The trailer for the second film even includes a clip of Martin’s mother holding his scrapbook and exclaiming: “What is this??? One hundred percent medically accurate??? Is this a perverted film you’ve been talking about???” neatly closing the self-promotion loop (the self-promotion centipede?) of film and film marketing.

The third film, inexplicably a comment on the US prison system, does much the same. The actors who played the villains in the first two films are back as other characters (the resemblances don’t go unmentioned), and decide the best way to handle prison overpopulation is, of course, a human centipede. Lawrence R. Harvey waves DVD copies of the first two films around, leaves them on Dieter Laser ‘s character’s desk, and invites Tom Six himself to visit George H.W. Bush Prison (like the first film, getting into the themes of The Human Centipede 3 (Final Sequence) would require more time than I’m willing to dedicate to such muddled metaphors) to watch the surgeries take place. Everyone from the prison doctor to the office secretary is “a big fan” of Six ‘s work.

Changing Times

The Human Centipede trilogy effectively built Tom Six ‘s reputation as a master of the grotesque, too. However, that moniker has lost some of its pull with the changing film industry in a moment when gimmickry is no longer horror’s bread and butter and “elevated horror” a la A24 and IPs like Halloween dominate culturally.

The hype machine Tom Six built still exists, as evidenced by memes, t-shirts, and Six’s own Tweets with compilations of references to the Human Centipede ranging from SNL sketches to interviews with Megan Thee Stallion (what he calls, “true pop culture, baby!” ). That being said, none of this has helped him get his latest film, The Onania Club released. Audience tastes, at least for now, seem to have moved on.

What do you think? Is The Human Centipede really the most horrific film ever made? Let us know in the comments!

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10 years of 'the human centipede' and its prediction of the alt-right.

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Not the good guy.

For a movie that only grossed $252,207 worldwide at the box office, The Human Centipede , which turns ten years old today, is a movie that has had an outsized cultural footprint (to be fair, it was mostly an on-demand release, and those numbers, though unavailable, are likely substantial). When it debuted at horror film festivals, outraged Tweets wondering what was wrong with the filmmakers became a trend. Among myself and my friends, it became known as the movie that would make your girlfriend punch you for even describing the plot, in which three people are surgically sewn together, anus-to-mouth. A year later, it was parodied on South Park , and became a thing that everyone just knew about, spawning twisted three-person Halloween costumes and unofficial spin-off merchandise. The sheer uniquely disgusting nature of the central plot point was just weird and gross enough to capture people's imaginations, for better or worse.

My reaction at the time was that in some ways, here was a horror movie I had no good moral defense for. While I champion every film's right to exist, if an evangelical Christian tried to argue that the only point of The Human Centipede was to show filth and depravity, what rebuttal could I have? I couldn't see any larger thematic point being made or ground-breaking cinematic greatness achieved. It was very well made, but was that enough to justify it? Director Tom Six even admitted it began as a joke, when he thought about punishing convicted child molesters by sewing their mouths to the buttocks of a fat truck driver.

I was, it turns out, missing a lot. And once the movie became a trilogy, its larger points became a whole lot clearer.

Ah, but did Tom Six intend it to be a trilogy? The fact that the first movie is sub-titled "First Sequence" suggests so. The fact that the centipede itself is a three-parter, allegorical for both three act structure and movie trilogies, implies that the triptych itself is a human centipede of its own, with each successive installment feeding on the waste of the prior entry and making it nastier. Uniquely among trilogies, the Human Centipede series posits in each successive installment that the prior entries were just movies, and this is the real one. And in doing so, it makes significant points about how media — and bad ideas — are consumed.

Dr. Heiter (Dieter Laser) in the first film is never explicitly called a Nazi, but he is implicitly coded as one, from his taste in music to his misanthropy and affinity for medical experiments. He's what you would imagine Dr. Mengele to be. And he's rooted in both the notion of Europe reckoning with its fascist past, and Six's own fear of medical procedures. The anticipation and description of the surgery is almost worse than the actual cutting; Six uses this to spread things out and give us time to expect that maybe the victims will escape. Nope. If they had, the movie probably wouldn't be as memorable. Instead, it gives you the shocking thing you paid to see. And it ends with everyone either dead or dying.

But then, in the sequel, we meet Martin (Laurence R. Harvey), a socially awkward, physically unattractive, living-at-home introvert who becomes obsessed with the first film. And like so many toxic fans online, he identifies with Heiter rather than his victims — think Rick and Morty fans who somehow believe Rick is meant to be a hero and role model. He plans his own Human Centipede for real, which will involve one of the actual actresses from the movie. It's an elaborate plan, carried out in detail...and then, in the last moments of the film, we find it was just a fantasy. He doesn't have it in him to actually do the thing.

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The "It's all a dream" ending is usually a cop-out, but not here, and here's why: threats on the Internet by obsessive fanboys like Martin, in real life, blur the lines between fantasy and reality, deliberately. If caught, they'll claim their threats were just for the LOLz. But sometimes the threats involve actual stalking, or swatting, i.e. calling in a fake crime at the subject's home address, summoning police with guns drawn who may shoot someone by mistake. Feeling powerless, many of today's alt-right recruits idolize powerful figures both real and fictional, and draw up revenge fantasies about a world they feel rejects them. And yes, those are often directed at favorite actresses who wouldn't give them the time of day in real life, and the characters they admire are often fascist.

Part three takes it a step further. The next step is that those nascent Nazis invade real-world politics. In the third film, a maniacal, racist, misogynist prison warden (Laser again) is inspired by his accountant (Harvey again) to watch the first two Human Centipede movies. He does, and is inspired to make his real-life (mostly nonwhite) inmates into a centipede as a formal punishment. The idea has gone from a fringe Nazi concept, to something giggled at by Internet "incels" (involuntary celibates), to becoming actual policy — critics of the White House's "Muslim ban" architect Stephen Miller would say this describes him. It's no coincidence that Laser and Harvey play the inspired and the inspirations; it's a shorthand for saying that in fact, there's no appreciable difference between Nazis and people who flirt with Nazi ideas. The third film ends on a note that implies things will only get worse from here.

Back in 2009, the news cycle wasn't quite what it is today, but those looking could see a pattern: fringe blog says something outrageous (think "birtherism"), semi-mainstream commentator discusses it as an item worth considering, then mainstream news pick up on that commentator's take and make it a headline that begins "Some people are saying..." That cycle has only gotten worse, when the president retweets conspiracy theorists and says there are good people on both sides of a pro-slavery debate; meanwhile, right-wing actors like Adam Baldwin deliberately stoke the anger of hardcore video gamers by bolstering misogynist fears that women use sex to get good game reviews, and feminists are coming to ruin and censor violent or sexy titles. The mainstream media spends the day talking about it, the president (who got elected on some of this stuff) sometimes retweets it, until the next crackpot notion takes root in the online fever swamps. The regurgitation and egestion may be metaphorical, but it's a human centipede all its own.

Did Tom Six foresee how all of this would get, or did he just make a gross joke that accidentally became relevant? I don't know, and it doesn't matter. In The Human Centipede trilogy, he has made the perfect allegory for our time, one in which misplaced identification for the wrong people metastasizes, reprocesses, and turns a sick joke into a toxic society.

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The Human Centipede II (Full Sequence)

Dutch-born writer-director Tom Six is a man of his word, and his promise to make a far grosser follow-up to his 2009 horror hit is more than fully realized in "The Human Centipede II (Full Sequence)."

By Robert Koehler

Robert Koehler

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'The Human Centipede II (Full Sequence)'

Dutch-born writer-director Tom Six is a man of his word, and his promise to make a far grosser follow-up to his 2009 horror hit is more than fully realized in “The Human Centipede II (Full Sequence).” It’s also blacker (literally, with black-and-white lensing), more absurdist, minimalist, vapid and pretentious than the original, presenting a morbidly obese , mentally slow mama’s boy trying to top the mad scientist from the first pic. Hotly anticipated by the hardest-core layer of fanboy culture, pic unfortunately may demand a third experiment.

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“I always tell my friends,” Six states in his interview on the “Human Centipede” DVD, “that part one will be ‘ My Little Pony ‘ compared to part two,” and despite the first pic’s ample supply of medical/biological/psychological grossness, the sequel confirms that Six’s claim was no exaggeration. The first film’s German surgeon took his skills separating Siamese twins in a horrific direction by attaching two women and one man together, mouth to anus.

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The new angle here is that, while the first time it was only a movie, this time it’s real. Obsessed and, if you will, inspired by “ The Human Centipede ,” pathetically fat Martin (Laurence R. Harvey, a Brit performance artist in a striking screen debut) lives with his whiny, pasty-faced mother (Vivien Bridson) in a dumpy London flat with only a pet centipede and a cherished scrapbook on the movie to keep his tiny heart afloat. Not improving matters is incompetent Dr. Sebring (Bill Hutchens), who suspects Martin’s emotionally stunted personality stems from his abuse at the hands of his incarcerated (and unseen) dad.

Add to the mix some boorish neighbors who play their post-punk music at ear-deafening levels, and you have a world that flagrantly displays the various influences of Joe Orton, Francis Bacon, Joel-Peter Witkin, Samuel Beckett and David Lynch, as captured in cinematographer David Meadows’ monochrome HD wide-angle lensing. But as the rest of the film shows, while Six has tapped into the stylings of great artists (much as he did with David Cronenberg, Stanley Kubrick and Michael Haneke in the first film, which was as white and glistening as this one is dark and muddy), he remains incapable of sustaining his thin and disgusting concept over feature length.

Once Martin snaps when his mom rips up his scrapbook, nothing is quite the same, and he proceeds to leave a trail of at least 20 corpses before the end credits. Propping up dead mom at the family dinner table with her horrifically bashed-in skull is only the intro to a sequence in which Martin goes on a killing/collecting spree, gathering 12 naked, bound and gagged victims for an experiment mimicking the first film’s stunt.

Key to Martin’s perversion is his yen for self-mutilating masturbation while watching the “Human Centipede” DVD at his workstation, offering the film’s only sliver of insight into the corpuscular, googly-eyed and nearly wordless lad’s state of mind. The latter half of the pic’s action comes as close to the porn half of the porn-horror subgenre as any filmmaker has managed to date, and it’s enough to have convinced the British Board of Film Classification to refuse “Human Centipede II” a certificate, thus preventing DVD or VOD release in the U.K. (which were the only planned platforms).

Six’s half-developed sense of humor trickles in when Martin picks up Ashlynn Yennie (the actress who played the rear part of the original three-person “centipede”) at Heathrow, luring her with the promise of an audition with Quentin Tarantino. Of course, there’s no Quentin, and Yennie soon realizes she’s in the “reality” aftermath of the movie she co-starred in, with no way out of one of the world’s most disturbing warehouses.

More boring than stomach-churning, the film nevertheless contains scattered scenes and sequences so far beyond the tolerance of the squeamish that it can’t be overstated; one, detailing the violent birth and death of a baby, is here simply to shock the most jaded of the jaded. It also displays the fact that Six has a somewhat larger budget this time for more grossness and disgust, which his tech crew delivers with relish.

Production: An IFC Midnight (in U.S.) release of a Six Entertainment production. Produced by Ilona Six, Tom Six. Executive producer, Ilona Six. Directed, written by Tom Six.
Crew: Camera (B&W, HD), David Meadows; editor, Nigel De Hond; music, James Edward Barker; production designer, Thomas Stefan; art director, Stephan Johannes; set decorators, Benjamin Joffe, Tom Mangel; costume designer, Harriet Thompson; sound (stereo), Henry Milliner; sound designer, Eilam Hoffman; supervising sound editor, Hoffman; re-recording mixers, Graham Daniel, Adam Daniel, Srdjan Kurpjel; special effects supervisor, Jonathan Bullock; special effects prosthetics supervisor, John Schoonraad; assistant director, Clare Finnegan; casting, Six Entertainment. Reviewed at RealD screening room, Beverly Hills, September 28, 2011. (In Fantastic Fest -- opener.) Running time: 90 MIN.
With: With: Ashlynn Yennie, Laurence R. Harvey, Vivien Bridson, Bill Hutchens.

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#198 – Meghan Barrett on challenging our assumptions about insects

On this page:.

Introduction
1 Highlights
2 Articles, books, and other media discussed in the show
3.1 Cold open [00:00:00]
3.2 Luisa's intro [00:01:02]
3.3 The interview begins [00:03:06]
3.4 What is an insect? [00:03:22]
3.5 Size diversity [00:07:24]
3.6 How important is brain size for sentience? [00:11:27]
3.7 Offspring, parental investment, and lifespan [00:19:00]
3.8 Cognition and behaviour [00:23:23]
3.9 The scale of insect suffering [00:27:01]
3.10 Capacity to suffer [00:35:56]
3.11 The empirical evidence for whether insects can feel pain [00:47:18]
3.12 Nociceptors [01:00:02]
3.13 Integrated nociception [01:08:39]
3.14 Response to analgesia [01:16:17]
3.15 Analgesia preference [01:25:57]
3.16 Flexible self-protective behaviour [01:31:19]
3.17 Motivational tradeoffs and associative learning [01:38:45]
3.18 Results [01:43:31]
3.19 Reasons to be sceptical [01:47:18]
3.20 Meghan's probability of sentience in insects [02:10:20]
3.21 Views of the broader entomologist community [02:18:18]
3.22 Insect farming [02:26:52]
3.23 How much to worry about insect farming [02:40:56]
3.24 Inhumane slaughter and disease in insect farms [02:44:45]
3.25 Inadequate nutrition, density, and photophobia [02:53:50]
3.26 Most humane ways to kill insects at home [03:01:33]
3.27 Challenges in researching this [03:07:53]
3.28 Most promising reforms [03:18:44]
3.29 Why Meghan is hopeful about working with the industry [03:22:17]
3.30 Careers [03:34:08]
3.31 Insect Welfare Research Society [03:37:16]
3.32 Luisa's outro [03:47:01]
4 Learn more
5 Related episodes

In today’s episode, host Luisa Rodriguez speaks to Meghan Barrett — insect neurobiologist and physiologist at Indiana University Indianapolis and founding director of the Insect Welfare Research Society — about her work to understand insects’ potential capacity for suffering, and what that might mean for how humans currently farm and use insects.

They cover:

The scale of potential insect suffering in the wild, on farms, and in labs.
Examples from cutting-edge insect research, like how depression- and anxiety-like states can be induced in fruit flies and successfully treated with human antidepressants.
How size bias might help explain why many people assume insects can’t feel pain.
Practical solutions that Meghan’s team is working on to improve farmed insect welfare, such as standard operating procedures for more humane slaughter methods.
Challenges facing the nascent field of insect welfare research, and where the main research gaps are.
Meghan’s personal story of how she went from being sceptical of insect pain to working as an insect welfare scientist, and her advice for others who want to improve the lives of insects.
And much more.

Producer and editor: Keiran Harris Audio engineering by Ben Cordell, Milo McGuire, Simon Monsour, and Dominic Armstrong Additional content editing: Katy Moore and Luisa Rodriguez Transcriptions: Katy Moore

Size diversity

Meghan Barrett: You’ve seen a lot of insects; you’ve probably mostly seen small ones. But it turns out that this is not characteristic of the entire group. Insect species vary by a factor of about 5.2 million in body mass from the smallest to the largest. So to give you some context for that, from a vertebrate perspective, birds are our flying terrestrial vertebrates; insects are our flying terrestrial invertebrates. Birds only vary by a factor of about 72,000 in body mass, whereas in insects, it’s 5.2 million. And so we’ve got really, really, really tiny insects like parasitic wasps and featherwing beetles that are super, super small — like, on the scale of some cells, single-cell organisms: they’re the same size as those, which just also goes to show you how big those can even get. Life is very diverse. Then we’ve got these gigantic beetles that if you were to put one on the palm of an adult’s hand, would cover from the palm all the way to the fingertips in the longhorn beetles. We’ve got giant Goliath beetles, we’ve got huge stick insects — just really, really big insects are also a thing that we have, and people just tend to be less familiar with them. One example I like to give, again from a vertebrate perspective, where I think we’re more familiar: there’s some beetle larvae that even weigh three to five times the mass of a house mouse, called Megasoma actaeon . So if you are willing to give mice the benefit of the doubt on a body size perspective, at least these beetle larvae — which are not the ones I would choose, by the way; if I was going to give an insect the benefit of the doubt, beetle larvae wouldn’t be where I go first — but if it’s all based on body size for you, I guess that’s where you’re going to be. Luisa Rodriguez: Yeah. The thing that really strikes me about that fact is I put a lot of weight on mice having capacity for pain and also pleasure, probably. And it is crazy how much just the fact that a beetle larva is much bigger than a mouse already flips my brain into being like, well then sure, it could be sentient too. Like, so much of my intuition clearly must be riding on a random size heuristic: as soon as you tell me bugs are big, I’m like, oh, in that case, sure, maybe we’ve got more going on than I thought. Meghan Barrett: Yeah. I think that body size does a lot of work for a lot of people’s intuitions. That’s why I like to start with facts like this, just to demonstrate how diverse insects are. And also maybe that this is a group of animals I think people are particularly unfamiliar with. They are especially poorly covered in our science curriculum; they are especially poorly understood, because people don’t spend as much time learning about them at museums; and they’re just harder to spend time with in a lot of ways, I think, for people. So people have pets that are vertebrates that they take care of across the taxonomic groups, and people get familiar with those from going to zoos and watching their behaviours there, and watching nature documentaries and more. But I think the insects are still really underappreciated, and that means that our intuitions are probably more likely to be wrong than with those other groups.

Offspring, parental investment, and lifespan

Meghan Barrett: Yeah. So we talked about body size. We talked about the evolutionary history of that. Let’s chat a little bit then about the life history bit of this. I think most of us believe that all insects are producing a really large number of offspring, they’re not really investing anything in those offspring from a parental perspective, and then those offspring are all going to develop really quickly and live really short lives. This is the thing everybody believes about all of the insects. Like, it must be true. This is not true. I can challenge each of these points for you, depending on which insect we’re talking about. And again, this isn’t to say that no insects do this. Many insects do have that kind of life history, but certainly not all of them. One example here would be that we do have insects that lay a large number of eggs, but we also have insects that are going to lay their offspring through the process of live birth. So one example of that would be this fly species that develops its offspring kind of in utero, feeding off of an internal milk gland, and then right before that larvae would pupate, it gives birth to that larvae. So they raise them one at a time that way. Each of those female flies averages about four and a half offspring over the course of her life. So they are certainly not rearing large numbers of offspring with low parental investment. There are lots of examples of parental investment across the insects — ranging from absolutely no care, “I’ve laid my eggs on that leaf, and I’m outie,” all the way through really high parental investment, like you see in your eusocial termite colonies or even your subsocial wood roaches. Both of those are examples of monogamous biparental care. And for termites, those monogamous pairings of the queen and the king can actually last for 20 years at a time. There are ants, queen ants can live up to 30 years, they’ve seen so far, too. So there are insects that live quite a while and have large numbers of offspring, in both of those cases — although not reproductively viable offspring, because, of course, they produce relatively fewer reproductively viable additional queens and kings, and much more just sterile worker castes and stuff like that. We don’t just see this in the social insects. I think we tend to give the social insects a lot more credit than the solitary ones, so I want to call out that the solitary ones also do some pretty cool stuff. You’ve got these male water bugs that will carry the eggs on their back to protect them from predation events and things like that. It actually has fitness consequences for those males to do that parental investment. And there’s lots of examples for female earwigs and things like that as well. And then on that point of living very short lives, there’s variation both in the developmental and the adult life stage in terms of lifespan. So you’ve got super short lifespans in your mayflies — all the way down to five minutes at the adult life stage; like they are out and they are reproducing, and they’re done — all the way up to, like I just mentioned, those queen ants living for 28, 30 years.

Headless cockroaches

Meghan Barrett: You can imagine that insects have a neck, basically, that attaches their body to their head, so they have an ascending nervous system pathway that’s going from the body to the brain, and then they have a descending nervous system pathway from the brain to the body. We have this too. And it’s important to have both of these, because that’s how information gets to the brain, and then how the brain controls your motor function and stuff like that in a goal-directed manner, is through your descending nervous system. So what we can do, for example, and has been done in the cockroach, is we can actually take readings from the ascending nervous system and say, is that system being activated as we apply certain signals to parts of the body? And we can do the same on the descending side if we choose to. For example, this one really great study by Emanuel and Libersat in 2019 , they basically applied non-noxious tactile stimuli — so just like touching a bug, but it’s not painful or expected to be painful — and then noxious heat stimuli to the abdomens of these cockroaches. What they found, recording that neck connective, the ascending activity, is that it shows a really weak response to that touch stimuli, but a very strong, persistent response to that noxious heat stimuli. So we know that stimuli is sending some kind of signal to the brain, and the signal is different from just being touched in an innocuous way. So that’s really relevant data, I think. The other thing that’s really interesting about the research that they did is… So there’s some research that shows that headless insects, just like headless animals of the vertebrate kind, can actually sometimes perform reflexive responses to noxious stimuli. So what they did was cut the heads off of these insects and see if they responded in the same way to the noxious stimuli as when they were fully intact. So the headless cockroaches were unable to mount a full escape response to the noxious stimuli. They could only do this kind of startle reflex that the ventral nerve cord type nervous system is capable of doing on its own. So clearly something important is happening in the brains of these cockroaches to exert descending control over their behaviours in response to this noxious heat stimuli. And this should, again, just be taken as some evidence that these signals are making it to the brain, and that it’s important that they make it to the brain for the fitness of the animal.

Is self-protective behaviour a reflex?

Meghan Barrett: There’s also been some research on crickets in the ’90s . They were interested in what stops male crickets from engaging in courtship behaviours. And they gave shocks and heat stimuli and also gave some strong pinches to the epiphalus, which is [part of the] the male reproductive organ. And they found that the insects would groom the epiphalus and stop mating also in those particular cases, when a strong enough pinch was delivered, even when no fluid leaked out of the body cavity as a result. So when you see the fluid leak out, now you have a confound, because maybe they’re grooming to get that fluid off of the body part they want to use. But when you don’t see that fluid leakage, and you just have the pinch delivered to that body part and they’re still grooming it, that suggests something else might be going on. Luisa Rodriguez: OK. And again, grooming feels like my brain can tell a story for how that would be reflexive. Do we have reason to think that it’s pain motivated? Meghan Barrett: We definitely have reasons to think it could be reflexive. I mean, again, each of these criteria you can explain as a reflex mechanism, and people did that in dogs for centuries. People were like, “These dogs are just little reflex machines. When I vivisect them and they make loud noises, it’s just their body having a reflex.” That’s Descartes: he was very convinced that vertebrate mammals that were not humans did not have minds like we have minds, and did not feel pain the way we feel pain. So again, I think it’s a question of accumulating a large enough number of objective proxies with similar enough mechanisms that we should start to be worried. And I worry that we are often interested in explaining things as a reflex, and that is one simple explanation. But another simple explanation is all of these things are showing up mechanistically similarly and induce similar fitness-relevant behaviours, and have underlyingly similar neurobiological structures to some degree. At what point do we say the simplest explanation is that probably this is producing a similar kind of experience? There are two ways to cut that simplicity question. One thing I think we often do is we think, if the insects are sentient, then too much of life is sentient. I mean, that’s everybody, right? That’s all of life, if the insects are sentient. But we’re forgetting how much other life there is out there that is succeeding without — we think — being sentient. The vast majority of species and individual organisms out there in the world do not even have nervous systems at all. Bacteria make up the vast majority, we believe at this time, the best evidence suggests. Although I will tell you, the microbiologists are having a conversation about what it even means to be a species. So don’t come at me, microbiologists. I know it’s complicated. So including insects in our group of organisms that might plausibly be sentient doesn’t actually expand, in terms of our whole conception of life, that much who makes the cut. We are missing, from our view, a large portion of who is alive.

If insects feel pain, is it mild or severe?

Meghan Barrett: There’s actually a chapter that’s dedicated to the kinds of cognitive processes that we think could influence the degree or severity of pain in different animals. One thing that’s challenging, though, and that chapter really explores in depth, is that you could imagine ways that a capacity could both increase or decrease the severity of pain for an animal. Like, imagine [mental] time travel. So in some ways you could imagine that [mental] time travel could make your pain more severe because you’re remembering previous times you were in pain, and you know how long the pain is going to last, and so that makes you feel even worse. Or you could imagine, you know how long the pain is going to last. You know it’s temporary. So even though it really hurts, you know it’s going to be over, and that makes it hurt less for you than for an animal that doesn’t have [mental] time travel, and is just stuck in the present moment of that pain for as long as it lasts. The other piece of theory that I think is compelling to me is this idea of would it be beneficial, from an evolutionary perspective, for an organism to have tiny pains? Like, what is the point of a pain? The point of a pain is to motivate you very strongly against an extremely fitness-relevant experience. Would it be relevant to be just a little motivated to avoid those kinds of things? Or should we expect these animals to be really motivated to avoid these things? The last thing I think from the tininess perspective is just to recall that point we discussed earlier about having more neurons. It’s not like each neuron creates the experience of pain for me. So it’s not like three of my neurons have fired, so I’m having a three-neuron pain as compared to 300, I’m having a 100x type of pain. Instead, it’s just like with the visual system and things like that, where having more neurons doesn’t necessarily mean you have more discrete pictures; it might just mean you have better resolution or a more complicated experience to some degree somehow. So it might just be more about repeating modules than it is about creating a bigger experience. And I think that’s something we’ll have to figure out as well. But just being tiny probably doesn’t provide us reason to think that they might have tiny experiences. Luisa Rodriguez: Could it be that… I can imagine lots of pain being terrible for fitness, like we could feel in theory much more pain, but that might paralyse us, keep us from doing things that might help us. And it seems like lots of insects might live in very dangerous environments. And it seems at least possible to me that there are so many life-threatening stimuli that feeling extremely intense pain about all the dangerous things is not actually evolutionarily fit as a strategy. But I don’t really know where that’s coming from, so I’m just curious if you have a reaction. Meghan Barrett: This is interesting. Yeah, let’s explore this a little bit. I think the first thing that comes to mind for me is that you’re right. When an organism is in an environment that is constantly exposing it to noxious stimuli, we do often see changes in the nociceptive neurobiology of that species. A great example comes up in the mammals, where we look at naked mole-rats. They live in these subterranean burrows, and because there’s a bunch of them, because they’re eusocial mammals, they’re constantly engaged in respiration, so they’re releasing CO2 into their environment. And that CO2 gets trapped underground with them in their burrows, because there’s nowhere for it to go, because there’s soil all around. So that can actually lead to tissue acidosis of their exterior surface. What they’ve found is that in naked mole-rats , they actually lack responsiveness to tissue acidosis in the periphery. They’ve evolved this mechanism, neurobiologically, that blocks signalling to the brain from the ion channels that are sensitive to tissue acidosis. We might ask, why is that? Well, from a fitness perspective, it’s probably not that great for a naked mole-rat to just be walking around all day constantly in pain due to some kind of damage, when its whole environment is necessarily going to cause that kind of damage. So it’s evolved something different than mice and rats, its close mammalian relatives, in its ability to experience pain — because it’s not fitness-relevant for naked mole-rats to be sensing their environment as constantly harmful. So we might imagine too that if we see insects that are adapted to live in super hot environments, they might not have thermal nociception at all, or they might have thermal nociceptors with a much higher activation threshold than the ones that insects in other environments might have. Certainly we could expect to see something like that, and I think that’s very plausible. Then it’s just what are the environments the animals are living in, and which kinds of nociception might they have lost or not lost? Because we don’t say naked mole-rats don’t feel pain just because they can’t feel that pain, right? They can feel other pains just fine. They feel thermal pain, mechanical pain just fine. So it’s just this one thing, but they still have the capacity for other kinds of pain.

Evolutionary perspective on insect sentience

Meghan Barrett: To come back to evolution — because we love to come back to the idea that sentience and pain evolved — this is also really important to think about, because if we’re going to be sceptical about sentience, we need to be sceptical about its evolutionary history, not just which organisms it’s in today. So we shouldn’t just be looking at the presence/absence of key features in this particular animal. We should be saying, where is this animal in the evolutionary tree? Who else am I confident is sentient? What does that mean about the likelihood this animal shares those features? And there are two possible hypotheses you could entertain here. One is the idea that sentience evolved exactly one time, and so everybody descended from that common ancestor, unless maybe they lost it for some reason, has that characteristic. So if you accept both vertebrates and any of the inverts — so a cephalopod or a decapod — if you’re convinced on a single invertebrate and you also are convinced on a single origin point for this, you have a problem, right? Because the closest common ancestor to all of those folks is very far back. And so you’re going to have all your insects, all your nematodes, all your decapods, all your annelids (which are another kind of worm) included, if you believe that there’s one common ancestor and no loss events. Now, maybe you think there’s loss events, but now you’re talking about multiple loss events, because there’s so many invertebrates. So you’re going to have to justify each of those losses, which you could potentially do. Another possible hypothesis is that sentience evolved multiple times independently in different groups. I would probably say this is more plausible in my view, in part because we see multiple emergence of things all the time in evolutionary history. Vision is a great example : we know that eyes might have evolved as many as 40 times during animal evolutionary history. And then, when we think about the development of eyes, it’s crucial to consider how they all generate the same basic function of being able to see something, even though they may vary in a lot of ways structurally. For instance, we saw the multiple emergence of what we call these crystalline lenses in the eyes of animals: some were made from co-opting calcite, others were made by co-opting heat shock proteins, still others were made by co-opting other novel proteins. All of them make these crystalline lenses, right? Or you could consider that independent but convergent evolution of similar structures in vertebrate eyes and spider eyes — and that can result in, again, the same basic capacity to see something. Of course, then we can talk about how the exact functions of seeing using these different structures or similar structures can vary. You know, acuity can vary, or wavelengths that the animal can sense can vary. But still, we think that same basic capacity of some kind of sight is there for all of these animals. This is all to say that it makes it more complicated if we’re looking for something like consciousness. So the function we’re interested in is consciousness instead of vision. Now we’re saying that if there’s more than one origin point, we need to be looking for potentially divergent structures capable of producing that common basic function. And of course, that common basic function can have lots of variance and gradation. And we don’t even have a good grasp yet on human consciousness , so you can see how acknowledging the possibility of multiple independent origins would then make this all very challenging to figure out. But in any case, I think when you look at this from an evolutionary perspective, it’s important to consider who’s a close relative? Who are your common ancestors for that group? When you think these characteristics evolved, why do you think they evolved there? And then, if you’re somebody who takes crustaceans seriously, given that their close relation is the insects, you’re going to need to seriously consider the hexapods too.

How likely is insect sentience?

Meghan Barrett: I think it’s likely enough that I’ve changed my whole career based on it. I was an insect neuroscientist and physiologist by training. I was researching climate change-related topics and the thermal physiology of insects, and I was researching how insect brains change in response to the cognitive demands of their environment or allometric constraints associated with their body size. And I was doing that quite successfully and having a lovely time. And I find these questions really scientifically interesting. I have, if you look at my CV, probably somewhere to the tune of 15 to 20 publications on just those two topics alone from my graduate degree days and my postdoctoral work. And I was convinced enough by my review of this evidence to switch almost entirely away from thermal physiology and very much away from neuroscience — although I do still retain a neuroscience piece of my research programme — to work on insects farmed as food and feed, and their welfare concerns, and trying to make changes to the way that we use and manage these animals that improve their welfare. So I now have a bunch of publications about welfare. I’ll also say that many of my colleagues have been extremely open and pleasant about this conversation, but also some have been more challenging. And I don’t mean to say that in a negative way. I’m very understanding of the practical reasons why this conversation is uncomfortable for our field. There’s regulations that could come into effect that would be very challenging for many of us who research insects to deal with on a practical level. So I’m obviously sensitive to that as a researcher myself. But also, because, you know, I’ve heated insects to death, poisoned insects to death, starved insects to death, dehydrated insects to death, ground up insects to death — I’m sure I’m missing something that I’ve done to an insect at some point in my research career — but it’s uncomfortable now, the research that I do, reflecting on the research that I have done. And I can imagine others may feel judged by bringing up the topic, and thus feel defensive instead of exploring the current state of the theory and the research with an open mind. I think a lot of humility is necessary too, given all the uncertainty that we’ve talked about here. And that can be really uncomfortable and really humbling to be confronted with such a morally important unknown. So I try very hard to really take everyone’s concerns seriously — all the way from the rights-focused folks through the hardcore physiology “I’m going to research my bugs any way I want to” folks. I think it’s really important to try and bridge as much of the community of people who care about this topic one way or the other as possible with my own very divergent experiences. But I would just say that it hasn’t always been low cost in some cases. Personally, it hasn’t been low cost: it’s been a hard personal transition for me to make, and to continue to be in this career with the way that I see the evidence falling out so far. And it’s been, in some cases, professionally hard. So I’m convinced enough for that. And I think that’s something worth taking seriously. You know, I’m that convinced that I’m changing my own career, yes. But I’m also not so convinced that I think it’s 100% certain. I live constantly with professional and personal uncertainty on this topic. So I’m convinced enough to make major changes, but you’re not going to see me say insects are sentient, that I’m sure of any order or species that they are sentient. There’s a lot more evidence that I hope to collect, and that I need to see collected by the scientific community, and a lot more theoretical work that needs to be done before I am convinced one way or the other.

Articles, books, and other media discussed in the show

Meghan’s work:

The Barrett Lab on insect welfare and sentience research — check out Meghan’s latest blog post for concrete steps on how to get involved in this work: I’m into insect welfare! What’s next?
Insect Welfare Research Society , where Meghan serves as director, is a scientific society that offers support to academic researchers and students in this space and created the first guidelines for protecting and promoting insect welfare in research settings
Is it time for insect researchers to consider their subjects’ welfare? (with coauthors)
Challenges in farmed insect welfare: Beyond the question of sentience (with Bob Fischer)
Can insects feel pain? A review of the neural and behavioural evidence (with coauthors, led by Matilda Gibbons) — research summary on the Effective Altruism Forum summarising an article published in Advances in Insect Physiology (2022)
The era beyond Eisemann et al. (1984): Insect pain in the 21st century (with Bob Fischer) — currently a preprint
Entomologists’ knowledge of, and attitudes towards, insect welfare in research and education (with Bob Fischer and M.L. Drewery)
Black soldier flies
Yellow mealworms
A peer-reviewed study on instantaneous, and thus more humane, grinding of black soldier fly larvae
A peer-reviewed study on long-read draft assembly of the Chinese mantis (Mantodea: Mantidae: Tenodera sinensis) genome revealing patterns of nociceptive ion channel gain and loss across Arthropoda (with Jay Goldberg and R. Keating Godfrey)
A post on drawing attention to invasive Lymantria dispar dispar spongy moth outbreaks as an important, neglected issue in wild animal welfare (with Hannah McKay)
Pain and suffering in farmed animals: First steps towards better understanding and management (Musk and Clutton, 2024) – Insects

Foundations to think about invertebrate sentience and welfare:

Meghan’s personal list on the EA Forum for readings about the plausibility of insect sentience and welfare — which includes both more positive and more sceptical authors on the list
Research library of 300+ articles collected on invertebrate welfare and sentience by the Insect Welfare Research Society
Numbers of insects (species and individuals) from the Smithsonian
Insects raised for food and feed — global scale, practices, and policy by Abraham Rowe
The rebugnant conclusion: Utilitarianism, insects, microbes, and AI systems by Jeff Sebo (also discussed in a previous interview with Luisa )
The Moral Weight Project Sequence
Animal Ethics: A Contemporary Introduction
Weighing Animal Welfare (to be released in 2024)
Review of the evidence of sentience in cephalopod molluscs and decapod crustaceans — a report for the UK government by former guest of the show Jonathan Birch et al.
Sentience in decapod crustaceans: A general framework and review of the evidence by Andrew Crump, et al.
Opinion: Estimating invertebrate sentience by Rethink Priorities researchers
Fine-tuning the criteria for inferring sentience by Culum Brown
Independence, weight and priority of evidence for sentience by Elizabeth Irvine
The New York Declaration on Animal Consciousness
The Canadian Veterinary Medicine Association position statement on animal sentience

Invertebrate brains:

Arthropod brains: Evolution, functional elegance, and historical significance by Nicholas James Strausfeld
Are bigger brains better? by Lars Chittka and Jeremy Niven
Multimodal information processing and associative learning in the insect brain by Devasena Thiagarajan and Silke Sachse
Organization and functional roles of the central complex in the insect brain by Keram Pfeiffer and Uwe Homberg
Mushroom body evolution demonstrates homology and divergence across Pancrustacea by Nicholas James Strausfeld et al.

Nociception and pain:

Nociceptive pathway in the cockroach Periplaneta americana by Stav Emanuel and Frederic Libersat
Drosophila pain sensitization and modulation unveiled by a novel pain model and analgesic drugs by Wijeong Jang et al.
Chili-supplemented food decreases glutathione-S-transferase activity in Drosophila melanogaster females without a change in other parameters of antioxidant system by Uliana V. Semaniuk et al.
In search of evidence for the experience of pain in honeybees: A self-administration study by Julia Groening, Dustin Venini, and Mandyam V. Srinivasan
Wound-dependent leg amputations to combat infections in an ant society by Erik T. Frank et al.
Noxious stimulation induces self-protective behavior in bumblebees by Matilda Gibbons et al.
The TRP channels Pkd2, NompC, and Trpm act in cold-sensing neurons to mediate unique aversive behaviors to noxious cold in Drosophila by Heather Turner et al.
Validation of the forced swim test in Drosophila , and its use to demonstrate psilocybin has long-lasting antidepressant-like effects in flies
Self-medication in insects: Current evidence and future perspectives by Jessica Abbott
Bridging the gap: Wound healing in insects restores mechanical strength by targeted cuticle deposition by Eoin Parle, Jan-Henning Dirks, and David Taylor
Do insects feel pain? — A biological view by C. H. Eisemann et al. (1984; note Meghan considers many findings of this paper to be outdated and has written a response paper with Bob Fischer, currently undergoing peer review, that can be read as a preprint )
Do insects feel pain? Although deprived of parts of their bodies, some insects seem to feel no discomfort by Harold Bastin (1927)

Social, cognitive, and play behaviours:

Targeted treatment of injured nestmates with antimicrobial compounds in an ant society by Erik Frank et al.
Saving the injured: Rescue behavior in the termite-hunting ant Megaponera analis by Erik Frank et al.
Copy-when-uncertain: Bumblebees rely on social information when rewards are highly variable by Marco Smolla et al.
Bumblebees socially learn behaviour too complex to innovate alone by Alice Bridges et al.
Conspecific and heterospecific information use in bumblebees by Erika H. Dawson and Lars Chittka
Sensory perception of dead conspecifics induces aversive cues and modulates lifespan through serotonin in Drosophila by Tuhin S. Chakraborty et al.
Seeking voluntary passive movement in flies is play-like behavior by Tilman Triphan and Wolf Huetteroth
Do bumble bees play? by Hiruni Samadi Galpayage Dona et al.
Individual recognition is associated with holistic face processing in Polistes paper wasps in a species-specific way by Elizabeth A. Tibbetts
Specialized face learning is associated with individual recognition in paper wasps by Michael J. Sheehan and Elizabeth A. Tibbetts
Paper wasps form abstract concept of ‘same and different’ by Chloe Weise, Christian Cely Ortiz, and Elizabeth A. Tibbetts
Numerical cognition in honeybees enables addition and subtraction by Scarlett R. Howard et al.

Insect farming and welfare considerations:

Prospects of edible insects as sustainable protein for food and feed – a review by S. A. Siddiqui et al.
Life cycle assessment of edible insects for food protein: A review by Afton Halloran et al.
When do we start caring about insect welfare? by Tina Klobučar and David Fisher
No longer crawling: Insect protein to come of age in the 2020s by Beyhan de Jong and Gorjan Nikolik
The future of feed: A WWF roadmap to accelerating insect protein in UK feeds — a joint report by World Wildlife Fund UK and Tesco
Edible insects: Future prospects for food and feed security by the Food and Agriculture Organization of the United Nations
Ensuring high standards of animal welfare in insect production by the International Platform of Insects as Food and Feed
How France became the unlikely home of the insect-farming industry by Rachael Pells
How American cricket farmers raise bugs for us to eat by Elettra Wiedemann
Black soldier fly ( Hermetia illucens ) larvae enhances immune activities and increases survivability of broiler chicks against experimental infection of Salmonella Gallinarum by Jina Lee et al.

Other human uses of insects:

Scale of direct human impacts on invertebrates by Abraham Rowe
Sterile fly release programs of the New World screwworm — see also our video with Kevin Esvelt discussing the screwworm problem
Lives in the balance: The ethics of using animals in biomedical research: The report of a Working Party of the Institute of Medical Ethics by Jane A. Smith and Kenneth M. Boyd
A perspective on education in research ethics for entomology graduate students by Rebecca T. Trout et al.
Perspectives on the ethical use of insects in research by entomology graduate students at the 2022 Entomological Society of America student debates by Sandhi et al.
Reducing insect use in research through power analyses by Craig Perl and Colin Lynch
Forty years of solitude: Life‐history divergence and behavioural isolation between laboratory lines of Drosophila melanogaster by C.R.B. Boake et al.
Small-scale rearing of the black soldier fly, Hermetia illucens (Diptera: Stratiomyidae), in the laboratory: low-cost and year-round rearing by Satoshi Nakamura et al.

Other 80,000 Hours podcast episodes and resources:

Bob Fischer on comparing the welfare of humans, chickens, pigs, octopuses, bees, and more
Jonathan Birch on the edge cases of sentience and why they matter
Jeff Sebo on digital minds, and how to avoid sleepwalking into a major moral catastrophe
Hannah Ritchie on why it makes sense to be optimistic about the environment
Problem profiles: Factory farming and wild animal suffering
Career review: Academic research

Table of Contents

1 Cold open [00:00:00]
2 Luisa’s intro [00:01:02]
3 The interview begins [00:03:06]
4 What is an insect? [00:03:22]
5 Size diversity [00:07:24]
6 How important is brain size for sentience? [00:11:27]
7 Offspring, parental investment, and lifespan [00:19:00]
8 Cognition and behaviour [00:23:23]
9 The scale of insect suffering [00:27:01]
10 Capacity to suffer [00:35:56]
11 The empirical evidence for whether insects can feel pain [00:47:18]
12 Nociceptors [01:00:02]
13 Integrated nociception [01:08:39]
14 Response to analgesia [01:16:17]
15 Analgesia preference [01:25:57]
16 Flexible self-protective behaviour [01:31:19]
17 Motivational tradeoffs and associative learning [01:38:45]
18 Results [01:43:31]
19 Reasons to be sceptical [01:47:18]
20 Meghan’s probability of sentience in insects [02:10:20]
21 Views of the broader entomologist community [02:18:18]
22 Insect farming [02:26:52]
23 How much to worry about insect farming [02:40:56]
24 Inhumane slaughter and disease in insect farms [02:44:45]
25 Inadequate nutrition, density, and photophobia [02:53:50]
26 Most humane ways to kill insects at home [03:01:33]
27 Challenges in researching this [03:07:53]
28 Most promising reforms [03:18:44]
29 Why Meghan is hopeful about working with the industry [03:22:17]
30 Careers [03:34:08]
31 Insect Welfare Research Society [03:37:16]
32 Luisa’s outro [03:47:01]

Cold open [00:00:00]

Meghan Barrett: Most of us believe that all insects are producing a really large number of offspring, they’re not really investing anything in those offspring from a parental perspective, and then those offspring are all going to develop really quickly and live really short lives. This is the thing everybody believes about all of the insects. Like, it must be true. This is not true. I can challenge each of these points for you, depending on which insect we’re talking about.

There are lots of examples of parental investment across the insects — ranging from absolutely no care, “I’ve laid my eggs on that leaf, and I’m outie,” all the way through really high parental investment, like you see in your eusocial termite colonies or even your subsocial wood roaches. Both of those are examples of monogamous biparental care. And for termites, those monogamous pairings of the queen and the king can actually last for 20 years at a time. Queen ants can live up to 30 years, they’ve seen so far, too. So there are insects that live quite a while, and have large numbers of offspring in both of those cases.

Luisa’s intro [00:01:02]

Luisa Rodriguez: Hi listeners, this is Luisa Rodriguez, host of The 80,000 Hours Podcast .

Today’s interview is one of my favourite interviews I’ve ever done. It’s a long one, but I think it’s worth listening to the whole thing.

I spoke to entomologist Meghan Barrett about the evidence that insects might be sentient, and it was the most worldview-altering conversation I’ve had in a long time (years!).

Before preparing for the interview and then speaking with Meghan, I put some weight on insects being sentient, but not much. I also found the idea that we should consider insect welfare a top priority pretty far-fetched and alienating.

I’ve still got a fair amount of uncertainty about how consciousness works and whether or not there really is “something it’s like to be” a fruit fly… But the evidence that at least some species of insects feel some kinds of pain comes out looking surprisingly compelling to me.

Some facts that particularly blew my mind:

Researchers have induced depression-like states in fruit flies, and then successfully treated those fruit flies with antidepressants that work in humans!
Fruit flies don’t naturally have the ability to sense capsaicin — the compound found in chilli peppers that make it spicy — as noxious and will eat food with capsaicin without hesitation under normal conditions. But if you edit a fruit fly’s genes to be able to sense capsaicin as incredibly spicy in the same way humans do, and then only offer that fruit fly really spicy food to eat, it will starve to death before eating the food. On top of that, if you offer that fruit fly a painkiller like ibuprofen, it’ll eat enough to not starve.

Those are just a couple of examples, but the episode is full of other fascinating stuff.

So without further ado, Meghan Barrett.

The interview begins [00:03:06]

Luisa Rodriguez: Today I’m speaking with Meghan Barrett. Meghan is an insect neurobiologist and physiologist at Indiana University Indianapolis and also the founding director of the Insect Welfare Research Society . Thank you so much for coming on the podcast, Meghan.

Meghan Barrett: Thank you so much for having me. I really appreciate the opportunity to be here.

What is an insect? [00:03:22]

Luisa Rodriguez: So I hope to talk about which insects might feel pain, and how we would even know. But first, what is an insect? I have some sense that it’s actually a huge group, but I don’t know that much about their diversity or behaviours. And I guess, for the listeners, I’ll flag that there’s probably no getting around the need for some scientific terminology, but if you bear with us, I think we’re going to be using plain spoken language for basically all the rest of the interview.

Meghan Barrett: This is a great place to start. In fact, I think it’s an essential place to start, because there are so many misconceptions out there about what insects are. So I think beginning with that background knowledge is definitely best.

There’s a lot of ways we can think about answering that question. Maybe the best place to start is with the evolutionary history of insects and other arthropods. So when you think about arthropods, that’s your group of animals that are going to have that chitinous exoskeleton . And there’s two major clades in the arthropods: the chelicerata and the mandibulata. The chelicerata are your spiders, your scorpions, your mites, your horseshoe crabs; and then your mandibulata is everybody else. So that includes your myriapods, that’s your millipedes and your centipedes; your decapods like crabs and shrimp; and your hexapods, which contains the insects.

I think one thing that’s really interesting, just from that little snippet of information, is that spiders and millipedes and centipedes are not actually insects, even though I think a lot of people tend to think of them as insects. It’s important to note that there’s actually evolutionary distance between those groups.

Luisa Rodriguez: Yes, definitely me included.

Meghan Barrett: Yeah. So for me, when I’m talking about insects, I’m just talking about the hexapods that are also insects — because there are also non-insect hexapods. Arthropod diversity is wild.

Importantly, I think another fact that a lot of people don’t realise from this evolutionary perspective is that insects are thus actually most closely related to crustaceans. They form this group together called the pancrustacea , and that group shares a common ancestor.

Luisa Rodriguez: Got it.

Meghan Barrett: So I think that’s something else that people should consider. If you’re somebody who takes crustacean sentience seriously, and sentience is a trait that has evolved — it didn’t just appear in organisms as they are today, which I’m sure will be something we repeatedly touch on throughout this episode — if you’re somebody who believes that crustaceans are given the benefit of the doubt for you, for sentience, then you might also think that insects are worth giving the benefit of the doubt for some reasons as well, from an evolutionary perspective.

Luisa Rodriguez: Nice. Yes, that does seem important.

Meghan Barrett: Yeah. That’s the evolutionary side of things. Then I think you asked a little bit about diversity and behaviours. So those are about the extant species. We think there’s about 5.5 million species estimated to exist. So they are the most diverse group of extant animals.

Luisa Rodriguez: That’s crazy.

Meghan Barrett: Yeah, it’s pretty insane. Super, super diverse. We haven’t even named most of them; we’ve only described about a million of those 5.5 million estimated species.

And when you’re talking about this much diversity, I think one thing that becomes really challenging is there’s almost nothing they all share in common. So the things that they share in common are: they all have six legs at the adult life stage, they have this chitinous exoskeleton, they usually have wings at the adult life stage, they’ve got external mouthparts. And now we’ve sort of covered most of the things that they share in common, along with a common ancestor.

So I think when we are talking about this group, it’s important to highlight some of the assumption-challenging examples of how different they are, especially in relation to thinking about animals that could plausibly have moral status. And I think for me, when I talk with people about this topic, the three things that come up most frequently where people have assumptions about insects in relation to their capacity for sentience that matter, are going to be: assumptions about body size in the group, assumptions about life history in the group, and then assumptions about cognition and behaviour in the group.

So if you’ll stick with me for a little bit longer, I just want to give you the best hits of insect diversity in each of these areas, to give you a sense of what we’re talking about here when we say they’re really different.

Luisa Rodriguez: Great. I’m ready.

Size diversity [00:07:24]

Meghan Barrett: Let’s start with that body size bit. I think most people would say insects are all small, right? That’s a pretty common assumption that people have.

Luisa Rodriguez: Yes. That is my assumption.

Meghan Barrett: Yeah. And not based on nothing. You’ve seen a lot of insects; you’ve probably mostly seen small ones. But it turns out that this is not characteristic of the entire group. Insect species vary by a factor of about 5.2 million in body mass.

Luisa Rodriguez: What?

Meghan Barrett: I know. From the smallest to the largest. So to give you some context for that, from a vertebrate perspective, birds are our flying terrestrial vertebrates; insects are our flying terrestrial invertebrates. Birds only vary by a factor of about 72,000 in body mass, whereas in insects, it’s 5.2 million. And so we’ve got really, really, really tiny insects like parasitic wasps and featherwing beetles that are super, super small — like, on the scale of some cells, single-cell organisms: they’re the same size as those, which just also goes to show you how big those can even get. Life is very diverse.

Then we’ve got these gigantic beetles that if you were to put one on the palm of an adult’s hand, would cover from the palm all the way to the fingertips in the longhorn beetles. We’ve got giant Goliath beetles, we’ve got huge stick insects — just really, really big insects are also a thing that we have, and people just tend to be less familiar with them.

One example I like to give, again from a vertebrate perspective, where I think we’re more familiar: there’s some beetle larvae that even weigh three to five times the mass of a house mouse, called Megasoma actaeon .

Luisa Rodriguez: That is insane.

Meghan Barrett: Yeah. So if you are willing to give mice the benefit of the doubt on a body size perspective, at least these beetle larvae — which are not the ones I would choose, by the way; if I was going to give an insect the benefit of the doubt, beetle larvae wouldn’t be where I go first — but if it’s all based on body size for you, I guess that’s where you’re going to be.

Luisa Rodriguez: Yeah. The thing that really strikes me about that fact is I put a lot of weight on mice having capacity for pain and also pleasure, probably. And it is crazy how much just the fact that a beetle larva is much bigger than a mouse already flips my brain into being like, well then sure, it could be sentient too. Like, so much of my intuition clearly must be riding on a random size heuristic: as soon as you tell me bugs are big, I’m like, oh, in that case, sure, maybe we’ve got more going on than I thought.

Meghan Barrett: Yeah. I think that body size does a lot of work for a lot of people’s intuitions. That’s why I like to start with facts like this, just to demonstrate how diverse insects are.

And also maybe that this is a group of animals I think people are particularly unfamiliar with. They are especially poorly covered in our science curriculum; they are especially poorly understood, because people don’t spend as much time learning about them at museums; and they’re just harder to spend time with in a lot of ways, I think, for people. So people have pets that are vertebrates that they take care of across the taxonomic groups, and people get familiar with those from going to zoos and watching their behaviours there, and watching nature documentaries and more. But I think the insects are still really underappreciated, and that means that our intuitions are probably more likely to be wrong than with those other groups.

Luisa Rodriguez: Yeah, that makes sense.

Meghan Barrett: I had one last point on body size, if you’ll just entertain me for one more minute, which is that if you are excited about how big today’s insects are, you would have been very excited by how big we used to have, the arthropods over all of evolutionary history. So if you went back to the Carboniferous period, the ancestors of insects were very, very, very large in many cases. We had these dragonflies, like Meganeura dragonflies, and they had wingspans that were like two feet long. So if you think today’s bugs are big, yesterday’s bugs were really big.

And it wasn’t just insects that could get that huge. We had these other terrestrial arthropods too — like some species of Arthropleura that were six to eight feet long; they could weigh 50 kilogrammes. We’re talking myriapods — that’s a millipede or a centipede today — and they would be taller than me; they’d weigh as much as I do.

So when we’re thinking about sentience having evolved, it didn’t just show up in today’s much smaller bugs — rather, it evolved in time periods that could have had much larger arthropod ancestors.

How important is brain size for sentience? [00:11:27]

Luisa Rodriguez: Actually, before we go on, if I can ask one more question about this: I guess the thing I do care about in the context of this sentience discussion is brain size. It feels like brain size is at least more likely to be tracking the thing that I care about. And I guess I care about whether these very large insects also have very large brains, or if the beetle is mostly like other guts, as opposed to brain guts.

Meghan Barrett: This is a phenomenal question. I appreciate you asking it very much, and it’s very interesting to me. So I have a couple of points to make on the brain size piece of this. The first thing I’ll say is just that we should ask ourselves if more actually always means better or more sophisticated. That’s an assumption to challenge about our thinking about brains.

For example, elephants have more neurons and more brain mass than you and I do, and yet I don’t consider them more likely to be sentient than me. Same thing with blue whales. And that’s because we know a lot of those additional neurons are because they’re just bigger, and so they have more mass to control, right? They have more touch points they need to be able to integrate and things like that. So more doesn’t always mean more sophisticated; it can often just mean more of the same repeat unit that performs the same kind of function.

And that explains, very plausibly I think, this phenomenon that we see, where very small brains are capable of producing really complex abilities . I know we’re going a little into the third point I was going to talk about about complex behaviours, but insects are capable of things like numerical cognition, social learning, facial recognition, cognitive bias, and much more. And so because of this behavioural data and this complexity that we initially thought was just going to be something you find in vertebrates, and now we’re seeing it in invertebrates with pretty small brains like honeybees, this suggests that maybe those bigger brains aren’t actually better or more sophisticated — they just have more redundancies or repeating modules.

You could think of this as changing resolution or complexity of a capacity without changing the existence of that capacity itself. So imagine an image that has more pixels to it: it doesn’t change the fact that there’s still a picture; it just changes the resolution of that picture. Does that make some sense?

Luisa Rodriguez: Yeah, it makes perfect sense.

Meghan Barrett: So that’s part one to this: that first we should just challenge that basic assumption that bigger brains are necessarily better at producing a capacity at all.

The next thing we need to think about is whether or not they are actually that small, which is what you were asking initially. So here again, I want to give some examples from vertebrates and invertebrates to challenge our intuition that vertebrates are always bigger than invertebrates. Let’s first consider just the mammals, because I think we all feel really comfortable talking about mammal sentience. So the smallest mammal brain that we have studied so far weighs in at 64.4 milligrammes. That’s the Etruscan shrew.

Luisa Rodriguez: That is tiny.

Meghan Barrett: So shrews can get very small. Very, very small. And the body mass of that shrew is about two grams or so, give or take. So we get some pretty small mammals out there. When we look at the largest insect brain we’ve studied to date, it’s a solitary wasp, and it weighs in at 11.7 milligrammes. So that’s an insect with a body mass of about 0.5 grams. So [the body size of the wasp is] a quarter the size of the shrew. That makes that shrew’s brain just about six times larger than the insect brain. That’s a smaller difference than we see between humans and whales. So already, even if we’re just considering the mammals, we see relatively comparable brain masses [with the wasp].

Now, that’s just one level of looking at the brain. I want to also extend beyond just mammals now and consider other vertebrates you might take seriously — like your lizards, say. So our smallest lizard brain that we’ve studied is the Algerian sand gecko. The brain itself weighs about 10.8 to 11.8 milligrammes. So that is smaller than the wasp at 11.7.

Luisa Rodriguez: Yeah. Wow.

Meghan Barrett: So already we’re seeing vertebrates close or comparable to the invertebrates, depending on whether you’re talking about mammals or lizards.

And I would further complicate this by saying, as I just mentioned, we haven’t studied the largest-bodied insects yet for their brains. These wasps that we’ve studied are actually pretty small on the scale of all [insect] body sizes. Now, we don’t expect insect brains to scale isometrically with body size. What that means is that for every unit of body mass, you get the same unit, same amount of brain mass added each time. We get these [non-isometric] trends in most taxa, where as you get bigger and bigger, the amount of additional brain mass you get sort of slows.

So we don’t expect to see huge, huge numbers in those really large insects for brain mass, but I still think it’s reasonable to say that it would be larger than 11.7 milligrammes, which is the wasp brain that we know of so far. And that wasp brain is already comparable to vertebrates. So we know we’re already in the same ballpark on mass.

Now, you might not think that mass is like the most relevant metric, though, for considering the brain. That’s because we might think that actually things like neuron numbers, like the computational units of the brain, are more important.

One note I want to make on this is that I’m going to talk about whole brain numbers today, because that’s the only data that we have. But I again want to go back to our earlier point that not all neurons do all things: neurons are specialised for particular functions; they’re organised into functionally discrete regions. For example, wasps have many more optic lobe neurons than ants do. Optic lobe neurons are the ones that bring in visual information from the periphery. This is probably because wasps fly and have to bring in a lot of visual information really fast. I don’t think that all those additional optic lobe neurons are all that sentience-relevant. So if I counted those, I would think the wasps were more likely to be sentient [than ants], when really they just can process and input more visual information more quickly.

Luisa Rodriguez: Yes, that makes sense to me.

Meghan Barrett: So that’s one thing to keep in mind: that we don’t have good data on what are the sentience-relevant regions of the brain, and how many cells are in those regions. So instead we’re just going to talk about total neuron numbers, because that’s the data we’ve got so far.

So with that caveat, let’s think about neuron numbers. Let’s go back again to mammals, because we like starting with mammals, right? So, as far as I know, the smallest number of neurons we’ve found in any of the mammals so far is in the naked mole-rats, and that’s about 26.88 million neurons. The smallest studied vertebrate brain is, again, that Algerian sand gecko I mentioned before. It has about 1.8 million neurons. And it turns out that that wasp brain I mentioned to you before also contains 1.8 million neurons. So our gecko and our wasp are very comparable. They’re both about 15 times smaller than that of the naked mole-rat.

Something interesting to consider here is that if we just look across the mammals, that naked mole-rat has only one one-thousandth the number of neurons of an elephant. So again, there’s a lot more difference within the mammals than we’re seeing between our smallest mammals and even just the invertebrates that we’ve studied so far from an insect perspective. So I think, again, we might consider just that there’s a lot of reasons to be sceptical that insects have an unusually small number of neurons compared even to the mammals, much less the vertebrate lizards and snakes.

Luisa Rodriguez: Yeah. Interesting. I think I learned about 1,000 new facts there. Should we go back to the assumptions that we were challenging?

Offspring, parental investment, and lifespan [00:19:00]

Meghan Barrett: Yeah. So we talked about body size. We talked about the evolutionary history of that. Let’s chat a little bit then about the life history bit of this. I think most of us believe that all insects are producing a really large number of offspring, they’re not really investing anything in those offspring from a parental perspective, and then those offspring are all going to develop really quickly and live really short lives.

Luisa Rodriguez: Yes, this is a thing I believe.

Meghan Barrett: Yes, this is the thing everybody believes about all of the insects. Like, it must be true. This is not true. I can challenge each of these points for you, depending on which insect we’re talking about. And again, this isn’t to say that no insects do this. Many insects do have that kind of life history, but certainly not all of them.

One example here would be that we do have insects that lay a large number of eggs, but we also have insects that are going to lay their offspring through the process of live birth. So one example of that would be this fly species that develops its offspring kind of in utero, feeding off of an internal milk gland, and then right before that larvae would pupate, it gives birth to that larvae. So they raise them one at a time that way. Each of those female flies averages about four and a half offspring over the course of her life. So they are certainly not rearing large numbers of offspring with low parental investment.

Meghan Barrett: Yeah, they live a long time. There are ants, queen ants can live up to 30 years, they’ve seen so far, too. So there are insects that live quite a while and have large numbers of offspring, in both of those cases — although not reproductively viable offspring, because, of course, they produce relatively fewer reproductively viable additional queens and kings, and much more just sterile worker castes and stuff like that.

We don’t just see this in the social insects. I think we tend to give the social insects a lot more credit than the solitary ones, so I want to call out that the solitary ones also do some pretty cool stuff. You’ve got these male water bugs that will carry the eggs on their back to protect them from predation events and things like that. It actually has fitness consequences for those males to do that parental investment. And there’s lots of examples for female earwigs and things like that as well.

And then on that point of living very short lives, there’s variation both in the developmental and the adult life stage in terms of lifespan. So you’ve got super short lifespans in your mayflies — all the way down to five minutes at the adult life stage; like they are out and they are reproducing, and they’re done — all the way up to, like I just mentioned, those queen ants living for 28, 30 years.

Luisa Rodriguez: Decades, yeah.

Meghan Barrett: And at the juvenile life stage, you even have cicadas, which you might be familiar with — especially this year in the midwestern United States, where we’re having the emergence of some our long-awaited brood — and we know some species of cicadas will live for about 17 years as juveniles prior to their emergence as adults. So variation is common in all of these different characteristics.

Luisa Rodriguez: I am just getting this increasing sense of like, I think of the Mammalia, and maybe throw snakes and lizards in there as well, as this diverse natural wonderland with all of these different beautiful, special creatures. And then I’m like, and there are like six insects: there are butterflies, ants, ladybugs…

Meghan Barrett: You are not the only person who thinks that.

Luisa Rodriguez: And they’re fine. They’re definitely not like nearly as beautiful or special and unique … No, sorry. Meghan is making disappointed faces at me.

Meghan Barrett: My heart.

Luisa Rodriguez: But yes, you’re successfully challenging this perception. If anything, I’m like, it sounds like they have diversity along all of the same axes, and huge ranges.

Meghan Barrett: People are really underestimating insect diversity. Yeah, it’s a classic problem. Every entomologist will tell you this is like one of their major gripes, that people just don’t know about how cool and diverse the insects actually are.

Cognition and behaviour [00:23:23]

Meghan Barrett: And this brings me to the last point of my spiel, our last assumption on cognition and behaviour. I mean, we could do a whole podcast literally just on this. Insects’ behaviours are so cool. I will not make you do a whole podcast on this, even though I kind of want to. So I’ll just give you a couple of examples.

Luisa Rodriguez: I’m tempted, too. But yeah, let’s start with a couple.

Meghan Barrett: So I already mentioned things like numerical abilities. There’s some work in honeybees that suggest they can do things like addition and subtraction . There’s work on abstract concepts of same and different in wasps . There’s work on individualised facial recognition of paper wasps of other members of their colony. We’ve seen some examples of playlike behaviour in both fruit flies and bumblebees . We have things like social information transfer , we have rescue behaviours in ants , and wound treatment behaviours of other members of the colony in ants. We have courtship rituals; they can involve things like dances and songs and touches, and giving gifts to your partner to try and encourage them to mate with you. We have tool use, so there’s digging tools and blocking tools, and sponging tools, and acoustic baffles for increasing the sounds that they make to attract partners. There’s [putative] self-medication when insects are sick.

Like I said, I could just go on and on . There’s a tremendous amount of diversity, and there’s even some things that relate to specifically affective states . So when you look in the biomedical research field, the fruit fly is a really common model organism. And we’ll talk more about that I’m sure at length later, because it shows up over and over again in the research that people are doing on insect pain. But people use fruit flies as kind of model organisms for affective state disorders like anxiety and depression research.

So that, I just want to be clear, doesn’t prove that insects have those affective states. They have depression- like states, and anxiety- like states, and pain- like states; that doesn’t mean they have anxiety, depression, and pain. But it certainly should give us some reason to take this idea seriously, that they’re trending in that direction more than, say, plants.

Luisa Rodriguez: Right. Absolutely. And just to make sure I understand that last point, it’s like, when we want to test things like antidepressants, anti-anxiety medicines, painkillers, we test them on fruit flies because in some ways they respond to those things in ways that teach us about humans?

Meghan Barrett: That’s the idea, right. So we’re testing things first in what we think are these much simpler systems, where we have, especially for the fruit fly, a lot of understanding of its circuitry, its neurobiological circuitry, the connections between different neurons. And we can do a tonne of genetic manipulations because of some very cool things people have done in the past with fruit flies. So we can insert genes and have them be expressed just in particular cell types and stuff like that, or knock genes out of just particular cell types. And that lets us do a lot of mapping in a relatively less complicated system. But the goal here is to test those things with some future benefit to the study of those states in people. So we test the antidepressants here in the hope that that will give us some insight into people.

Luisa Rodriguez: Right. And it’s not like we’re not testing to make sure the antidepressant doesn’t kill the fruit fly.

Meghan Barrett: No. If it works.

Luisa Rodriguez: We’re testing to see if the response… Yeah, I mean, I completely feel like already, just the fact that we’ve apparently been using fruit flies as a model organism for these kinds of affective states and diseases for a long time is like a huge update to me.

Meghan Barrett: Yeah, it definitely raises the probability, right?

Luisa Rodriguez: Yeah, definitely. It definitely does for me, at least.

The scale of insect suffering [00:27:01]

Luisa Rodriguez: Let’s get into why insect suffering might be a particularly pressing problem. I think there are lots of dimensions here, so maybe we can start with the scale of the problem. I have the sense that it’s big, but I don’t know exactly how big.

Meghan Barrett: Yeah, for sure. I guess this depends a little bit on what you actually define as the problem. For me, I see all of insect, potentially all of arthropod, suffering as the problem. We have farms, we have wild settings, we have zoos, we have research settings. So we use and manage insects in a variety of contexts, and then there’s all the ones we don’t manage in the wild as well.

For many of these contexts, we don’t have a good understanding of how many individuals are actually affected — because nobody’s collecting that data, just to be transparent. So I’m going to give you some attempts at estimates that I’ve either seen other people generate or that I’ve done like a back-of-the-envelope-style calculation myself to try and get at the scale.

Luisa Rodriguez: Sure.

Meghan Barrett: So maybe we start with the biggest of these contexts, which is the wild problem . Here we’ve got the Smithsonian citing this estimate of 10 quintillion wild insects alive at any given moment. So they’re estimating about 200 million insects per person, or 300 kilogrammes of insect mass for every kilogramme of human mass. So there’s a lot.

Luisa Rodriguez: Yup, that’s a lot.

Meghan Barrett: Yeah. Regardless of whether 10 quintillion is the right number, if it’s in that ballpark, the number is a lot, we can safely say. And I think when we say numbers like 10 quintillion, my brain — I don’t know about your brain — but my brain is like, I can kind of understand the 10, but the quintillion is sort of beyond me.

Luisa Rodriguez: Quintillion is just like a bigger… It’s just the biggest number, I think. You get to, like —

Meghan Barrett: Some mathematicians would argue with you on that.

Luisa Rodriguez: Well, they don’t understand my human psychology. It just goes from many billions to quintillion, and it’s just a step, and then there’s nothing bigger than that.

Meghan Barrett: Yeah. So I try to put this in perspective in some of the presentations that I give. If you froze time right now, and then you began counting all of the insects that were alive in that frozen moment of time, and you could count, say, 10 of them a second, it would take you 32 billion years to count all of the insects alive at that frozen moment in time. So that’s seven times the age of the sun. It’s more than twice the age of the universe. You could have been counting insects before the Big Bang that were alive today, and you wouldn’t have finished twice over. Big number.

Luisa Rodriguez: Wow, what a great way to picture that.

Meghan Barrett: Yeah. When I think about that, I’m like, man, imagine counting 10 insects a second since the beginning of time. Worst job. Worst job.

Luisa Rodriguez: Yeah, sounds terrible.

Meghan Barrett: But I mean, just to think about that scale. Absolutely incredible. Then I think we can talk about some slightly smaller, but still massive scales. They’re going to feel really small now that we’ve covered that one.

So let’s talk about the farmed context. For those who aren’t familiar, we farm insects for a variety of applications. There’s species-control applications, pest-management applications, honeybees obviously for pollination services, as well as some other species of bees that we use for pollination services. We use flies to produce some kinds of protein for cell cultured meat. We produce silk, we produce dyes. We use insects for all those things.

And we use insects in this relatively new industry, at least in the West: the insects as food and feed industry. So this is where we are either breeding insects directly to consume them ourselves — hence food — or we’re breeding them to feed to other traditional vertebrate livestock animals, like fish and chickens and pigs — and in that case, then we’re talking about them as feed.

So there aren’t great numbers for each of these industries, but there’s been some work in 2020, and they estimated about 1–1.2 trillion insects farmed as food and feed that year . That same year, the FAOSTAT numbers estimated about 80 billion of all the chickens, pigs, cows, turkeys, all your terrestrial farmed vertebrates. So we’re talking just in that one industry, 14 times the number of insects being farmed as livestock compared to vertebrates in that year.

And like I said, this is a very new industry, so it’s growing very rapidly. There are some estimates, again from that same report, that are suggesting in the next couple of decades we’re going to see about 40 to 80 trillion additional insects being reared in that industry. So now we’re talking about that industry alone rearing 500 to 1,000 times the number of current vertebrate animals each year.

Luisa Rodriguez: That’s huge.

Meghan Barrett: So still big. Not as big as the wild context.

My one last context is the research setting. And that’s of interest to me, just because I am an insect researcher. It’s middling compared to everything else I’ve just mentioned before, so it hardly merits a mention in terms of scale, it feels like. But I’ve done some very speculative calculations looking just at fruit fly labs, and how many insects they might be using and rearing in particular. And so my very, very speculative, with wide error bars estimate is about 2.2 billion individual fruit flies in labs each year. And that’s just that species — we’ve got a bunch of other insect species that are being reared year round in labs and being studied. But just for that kind of powerhouse model organism, maybe about 2.2 billion is a good estimate.

Luisa Rodriguez: Yeah. Wow. That is all very striking. OK, so that’s the scale. And then I guess, from the outside, why might we think that at least some of these insects might be suffering? What are their lives like? I know that I’ve just probably fallen into the trap of simplifying massively by asking, “What are all of insects’ lives like?”

Meghan Barrett: All 5.5 million species: go!

Luisa Rodriguez: Yeah, exactly. Go, go, go! What are the kinds of things some insects might experience that you think about when you think about whether some insects might be suffering?

Meghan Barrett: Yeah, again, we’re not trying to get into any of the details. Broadest sense of the experience of insects and why we think they could be suffering, it’s for many of the same reasons that we think other animals might be suffering, right? They experience things like predation and injury, poor climate conditions, starvation from excess competition, disease, parasitism — all those kinds of things. When we think about them on farms , they might see things like cannibalism, poor nutrition, bad environmental conditions, inhumane slaughter methods, aggression from their conspecifics because of the density — all those kinds of things that we see in vertebrates, many of those are going to apply to invertebrates as well, that they will have those same experiences, if they have experiences.

And given that we tend to associate these experiences with negative fitness consequences for vertebrate animals, and they also tend to have negative fitness consequences for the invertebrate animals, we might expect there to be some reason to think that these events could also cause them to suffer, if they have the right neurobiology to produce those kinds of experiences. And as I’m sure we’ll talk more about later, when we start to look into the actual physiological responses of insects to these events, and the behavioural responses of insects to these events, we often see somewhat similar responses in some cases — and that, again, might also give us some reason to think we should be cautious about their potential for suffering in response to these kinds of negative events.

And I also want to note that, like you were saying, insect diversity is tremendous, and the kinds of contexts in which we find insects are tremendously diverse as well. So a lot of suffering is context dependent. There could be insects out there that are living very nice lives, and insects out there that are living very not-nice lives, and that can even be the same species in the same area, just separated by time.

There’s a post that I wrote on the spongy moth and outbreaks of invasive spongy moths that you can read. It’s just meant to be like a case study in an example of why insect lives might not always be great, and why they sometimes can be great. And we find in the first year of an outbreak, there’s much less competition, food is more abundant, predators are lower, disease is typically lower. Many of those insects might have a pretty decent time of it. I can’t say for sure; I haven’t asked them. But from the outside, looking at the literature on the topic, I would say it looks like if there was going to be a nice year to be an insect in an outbreak, it would be year one.

And by the time you get to years two and three, resource competition is super intense. Diseases are very widespread. These are diseases that liquefy the internal organs and tissues of the animal slowly, over like a week. Often they’re being treated with pesticides, and anthropogenically managed. Predators are more abundant because their populations have increased over the period of time that the outbreak has occurred. For all of these reasons, it may be really not nice to be an insect in outbreak year two or three for these cyclical spongy moth outbreaks.

So I think that’s a good example of how the same insect species, same area, but separated over time, can experience very different conditions and potentially very different suffering.

Capacity to suffer [00:35:56]

Luisa Rodriguez: Yeah, those are the kinds of things that seem really bad. And because there are actual fitness reasons for insects to at least potentially develop the kinds of capacities that would allow insects to avoid things that hurt them, that is some reason to think, at least from the outside looking in, that they might have the capacity for suffering.

Are there any reasons to think, again, from the outside looking in, that they don’t have these capacities?

Meghan Barrett: Oh, yeah. Absolutely. I think there’s some intuitive-feeling reasons to be sceptical, and that have led people to be rightfully sceptical in the past. One of those would be, I think, the exoskeleton. So when we are having emotional states, or when other mammals are having emotional states, because we have this flexible outer surface, we grimace, right? Our face moves. And so we’re able to do more than just move individual body parts in relation to each other. We’re also able to make expressions. Insects are locked in on an expression. It is whatever their exoskeleton’s shape is after they have stopped growing. And so it isn’t really possible for them to do anything, other than just move body parts in relation to one another, to express any kind of affective state.

I think that makes it really challenging for us, at least for me. I know when I look at my cat and my cat has been scared, I see it in the face, right? And we can talk about anthropomorphism and stuff like that, but I am talking about intuitions right now, and where they lead us. We can intuit things from mammals because we see things like ourselves in them. Because of the phylogenetic distance, the morphological distance, the physiological distance, the behavioural distance between us and insects, we are lacking a lot of those cues. And some of those are just not overcomeable, like that exoskeleton problem.

I also think one thing that has been a real red herring in the conversation about insect pain — even though I understand why people put so much focus on it — is their weird responses to grievous injury. There’s all this literature going back to the early 20th century, there’s pictures even of entomologists cutting the abdomen off of an ant , and the ant continues to consume food that’s in front of it. Or somebody cuts the leg off of a praying mantis and the mantis continues to mate. Or stabs a hole in a locust and the locust starts to eat its own guts.

And people are like, well, this is pretty compelling evidence that that group of animals doesn’t feel pain. And fair. Intuitive. In some ways intuitive. In some ways, actually, when you start to think about it, maybe not as intuitive, because we have some examples of weird things people have done, like cut their own arms off to escape starving to death in the middle of the mountains. So if I observed that as an alien scientist, I might find, without that full understanding of the species’s [or individual’s] context-dependent motivations, to be a very confusing example.

Luisa Rodriguez: Yeah. But to be fair, without hearing whatever counterargument you’re about to make, I do find that relatively intuitively compelling.

Meghan Barrett: Oh yeah, same. I mean, I definitely found that very compelling. And I think literally a century of people have found that very compelling. So there’s reason to be finding that evidence compelling. I think there’s the context dependency part of it, that people have written a lot about why this might actually be slightly less compelling . A second thing is that there are pieces of evidence of insects actually responding, it appears, to grievous injuries in other contexts. That provides some strength to the idea that this is a context-dependent phenomenon. Could be. Could be, right? I’m not saying it is, but could be a context-dependent phenomenon for insects.

I think also some other interesting point here is that grievous injury pain isn’t the only kind of pain that we can experience. So if I put some hydrochloric acid on my skin, that’s going to cause me pain. You might want to say that it’s not a mechanical injury, it’s a chemical injury — but you still might say it’s an injury. OK, what about thermal pain? Like when I touch something hot, that does not cause a break in my skin if it’s a small surface injury, and yet it still causes me pain.

So there are shock-based pains, there are heat-based pains, there are chemical pains. We know there are many kinds, and if we focus on just one of those kinds, we miss the complete picture of what might have been evolutionarily relevant to the animal. When we look at how insects respond to heat and shocks, their responses are much more similar to the vertebrates than when we look at their responses to things like mechanical injury. And so I think that’s also something worth taking seriously — that that is an incomplete view of the picture of this animal.

Luisa Rodriguez: Totally. I guess I have two reactions. On the one hand, I’m like, yeah, but it’s still pretty weird that you would cut the abdomen off an ant and it would keep eating. On the other hand, I don’t know, there are weird things about humans. It seems like at least some people, when they have really extreme life-threatening injuries, don’t actually feel any pain. So there are just weird things that happen, and maybe it’s just all a bit fuzzier than we think it is when we’re sitting in our armchair.

Meghan Barrett: It’s complicated.

Luisa Rodriguez: Yeah, I guess I do have another part of me that is, if all insects feel is pain from shocks and heat, that’s still a lot of stuff. That makes me want insects not to feel pain from shocks and heat, even if cutting them in half turns out not to be the really painful thing for them.

Meghan Barrett: Not quite so bad.

Luisa Rodriguez: Yeah. I just find that really interesting and compelling.

Meghan Barrett: Yeah. In the human case, we have this endogenous neuromodulation system. Because sometimes you experience pain, and all you have to do is escape that thing. You touch a hot stove, you pull your hand away, the threat is over. You have done the thing.

Other times, it’s like, I need to be able to modulate my response to this negative situation so that I can do something else besides be in pain. You can think of that rock climber who had to cut his own arm off : there was a lot of endogenous neuromodulation happening there, where he was able to overcome his pain response because he had to in order to survive, right? His own nervous system produced chemicals that helped him overcome that pain response, such that he could act on this other motivation that was more important.

We might think something similar can happen in insects. We can think of something similar happening when you watch a cat walking on a clearly injured leg, and it’s because it’s a prey animal and it is trying to escape from some other motivation, like a perceived threat or predator. So we know this is something that happens in animals.

The other thing that we know about this is that there’s a question of anecdata on prevalence that I think is really interesting. I myself have observed many insects not behaving as I would have expected in response to a grievous injury [in my research]. But I have also looked at examples of insects responding to grievous injury. And the question is, what are we reporting? And are we reporting on the frequency of it? It’s very weird to me when I watch an insect not respond the way I would expect it to to grievous injury. That really sticks out in my mind, because I’m like, wow, you’d really think, if somebody cut your abdomen off, you’d be a little bit more concerned. But when an insect is concerned and responds to that, am I actually making note of that as well in my publications? So there’s a little bit of a potential for bias there in reporting.

I study, or did study at least, mostly Hymenoptera , which are your bees, ants, and wasps. And people study a lot of navigation work in ants. One thing that they’ve done to kind of figure out whether or not or how ants navigate is trying to figure out if ants count their steps or if they use landmarks or some combination.

So imagine you cut the bottom of the legs off of an ant so that they take the same number of steps, but their steps are shorter because their legs are shorter, and then you glue little stilts onto them so that their legs are longer, then you can figure out, are they navigating based on visual landmarks, or are they navigating based on counting the number of steps they’re taking?

You imagine many of the ants that you cut the bottoms of their legs off did not end up being usable in your study, right? And I’m also imagining that right after you cut the legs off of the ants, often the first thing that they are doing is not immediately going back to their normal behaviours. They might have experienced some distress during the procedure, so often there’s some period post-manipulation where that animal might be engaged in behaviours that are abnormal but that are underreported — things that could include escape responses or grooming or wound tending, those kinds of things.

They’re underreported of course because they’re not an important result to the experimenter who’s interested in navigation, but they could be important for informing our understanding when we care about the prevalence of non-normal responses to injury in insects.

And then there’s also a question of timing here. Like, how long post-injury are we assessing the animal’s response, and how relevant would that pain response be to the animal at that time? For instance, in a person, a broken leg often stops being painful six months after the break, because it’s healed. So even though the bone might have reduced strength, it doesn’t pain us to walk on it. The pain isn’t beneficial from a fitness perspective to us. And that’s because the bone, the utility of it, is normal again.

And so if we imagine our ants, we cut off the bottom of their legs and after some recovery time, we’ll say 10 minutes, the wound at the bottom of their leg is clotted at that point. Insects, I should note, generally don’t have full healing of the exoskeleton for large wounds, like we might get full healing of our exterior surface. So you might imagine that once the clotting has occurred and protected that animal from infection, that’s basically as good as the animal is going to get, from that external protective perspective and utility perspective.

So if the limb is still usable, then actually the majority of what’s problematic for that animal about that injury, from a fitness perspective, is the fitness issue. So assessing their response to that injury 15, 30 minutes after it was delivered may not be that relevant to understanding the kinds of pains that might have been adaptive for insects to evolve. So perhaps it was only adaptive for them to evolve a sense of mechanical pain that lasts as long as the clotting process lasts.

And then there’s a whole other set of questions about if the biomechanics of injuries actually change when you’re very small in mass, or when you have an exoskeleton instead of epidermis like we do as our exterior surface. So we don’t really have time to get into that, but that’s another interesting understudied area relevant to assessing why insects may not respond like vertebrates do to mechanical damage.

And again, I’m not saying this is true; I’m just saying there are a host of alternative hypotheses that are worth investigating before we just say that insects don’t feel pain because they don’t respond exactly like me. Well, insects aren’t built exactly like you.

Luisa Rodriguez: Yeah, cool. I get a lot from that example. OK, so we’ve just talked about the fact that insects are much more complex and diverse than maybe many people think. We also talked about reasons to think from the outside that insects may or may not be suffering in the environment, in farms, and in research labs.

But because this is such a fundamental question — do insects feel pain? — and because we’ve touched on this topic a little bit before on the podcast — for example, in our episode with Jeff Sebo — but never super thoroughly, today we’re going to talk about insects’ capacity for suffering in a bunch of depth.

The empirical evidence for whether insects can feel pain [00:47:18]

Luisa Rodriguez: So let’s talk about the empirical evidence. You coauthored this review paper in Advances in Insect Physiology that tries to answer the question of whether insects can feel pain based on experimental evidence that we have about different kinds of insects. And you and your coauthors looked for evidence of the capacity for pain in six different orders of insects, which cover flies, mosquitoes, cockroaches, termites, beetles, bees, ants, wasps, butterflies, moths, crickets, and grasshoppers — which is already more insects than I knew existed before today — as well as a bunch of others.

Just to set us up, you covered both adult insects but also juvenile insects. And right off the bat, I’m curious: why bother?

Meghan Barrett: So this publication was led by Dr Matilda Gibbons, who is now a postdoctoral scholar at UPenn, concurrently with her dissertation research on motivational tradeoffs in bumblebees and other markers of potential pain in bumblebees. And then the lab heads that were running this are Jonathan Birch and Lars Chittka, and Andrew Crump and Sajedeh Sarlak are the other two coauthors that assisted with this.

I actually came onto the project a little bit later; they’d already sort of started to conceive of the project when I jumped on board. And this was probably the main contribution that I made to the structure of the paper, was asking that we do juveniles separately from adults. And I think everybody understood why, once I said it, but it was like, oh, this is going to be so much more work.

Luisa Rodriguez: Doubling the work, really.

Meghan Barrett: Oh, yeah. Well, at least doubling. Because of course, the problem with juvenile insects is that they go through multiple instars, and their brains actually develop across those instars. So actually, if you look at our work for juveniles, we’re not just looking at juveniles versus adults: we’re looking at early instars and later instars within the juveniles and also adults. It’s a disaster.

Luisa Rodriguez: And for non-entomologists, what’s an instar?

Meghan Barrett: An instar is like the life stage of an insect between moults. So as they’re growing, they start out really small, and then they’re going to shed their exoskeleton to become a little bit bigger. And each one of those periods before they’re shedding again is an instar. So when they’re coming out of the egg, that’s the first instar, then they moult, that’s the second instar, blah, blah. There are variable numbers of instars across the different species. They can have very few — like Drosophila just have three — or they can have 17 to 20, like you find in yellow mealworms. And they can actually vary within a species as well. So it’s not set for a species; some members of the species can have more instars than another. In some species, not in all — because of course, when you say something about an insect, you always have to say, “In some species, not in all.”

Now, one thing that’s really important to understand about insect development is that there are two major developmental strategies. There’s also some rarer ones that I’m not going to talk about, but the two major ones are called holometabolous and hemimetabolous development.

Holometabolous is complete metamorphosis. Think of your butterfly. It starts out as this kind of grubby little caterpillar thing that looks nothing like a butterfly. It eats and grows looking like a caterpillar. Then it turns itself into goo as a pupa, and then it emerges in this radically different morphological state, where it’s a beautiful butterfly. That is holometabolous development. It is the more derived, or more recently evolved strategy. And most insects, maybe 80% or so, are going to be holometabolous in how they develop.

The more ancestral way that insects developed is hemimetabolous development. This is incomplete metamorphosis. So here you are basically having insects emerge from the egg as a little tiny version of what they look like as an adult. So imagine a baby cockroach. Looks kind of like a big cockroach, just way smaller. It usually is also missing a couple of features: it doesn’t have its reproductive system set up yet; it doesn’t usually have wings. But it starts out like a little tiny cockroach, and it just becomes a bigger, bigger, bigger one until that final terminal moult, where it becomes a reproductively viable adult, with wings, typically.

So those are our two strategies. And what’s important is that it’s not just things like the reproductive system or the external morphology that changes over this period of time. The nervous system changes substantially over time based on these two different strategies. So in ones that go from being a larval grub-like form to an adult during pupation, there is an absolutely radical transformation of the nervous system. It’s going to differ, depending on the species, exactly how radical it is, but it’s always very extreme. When we look at our hemimetabolous insects, their brains actually have the same functionally discrete regions from the first instar all the way to adulthood, and they just kind of get bigger and bigger and more complex. But they have all the same kind of general organisation and plans from the jump.

So this is a really important difference when we consider the fact that sensory integration in the brain, and having those functionally discrete regions that are associated with sensory integration, is an important piece of evidence for whether or not a group of animals might be sentient. And so that’s why we wanted to trace juveniles independently from adults: their nervous systems are very different, and their behaviours are also very different.

Luisa Rodriguez: Yes, that makes complete sense. I have this intuition from human lifespans: I think that juvenileness is such a tiny fraction of the number of humans alive, because it’s such a short part of our lifespan. If I were going to think about whether humans feel pain, as a researcher, I’d focus on adults, because that’s just like most of the question or something. And I guess it’s possible, but I don’t know, and you will know: what fraction of the insects alive at any given time are juveniles? I can imagine it being a bigger percent depending on lifespan.

Meghan Barrett: I’m so flattered you think I would know that.

Luisa Rodriguez: To be fair, as I was asking, I was like, actually, this is maybe an incredibly hard question.

Meghan Barrett: I think that’s a very complicated question. Again, very flattered that you think I would know that off the top of my head. I think there’s so many factors that go into that. I do think where this comes to be most relevant to me is in the farming context, because that’s when we actually do have information. In the wild, I mean, that question is not possible for me to answer right now.

But on farms, the two species that are primarily reared that are holometabolous are the black soldier fly and the yellow mealworm. And they actually typically harvest those animals in the juvenile life stage, so they spend all of their life prior to slaughter as juveniles. A subset of them are retained to kind of continue the colony cycle and be breeders, but the vast majority of them going through that process are slaughtered as juveniles. For crickets, we actually do often see many crickets reaching all the way to adulthood, but they often can be slaughtered very early in adulthood as well. And so you might still see that, on balance, you’re getting more juvenile life days than adult life days.

Luisa Rodriguez: Cool. I basically was like, why bother looking at juveniles? And then I was like, come to think of it, I do feel like I know of some insects in farms that are either killed or experimented on as juveniles. So actually, that makes some more sense, and it sounds like that intuition is not crazy.

OK, let’s talk about how you looked for evidence of pain. In the report, you and your coauthors look at eight broad criteria that, if met, at least suggest that a given animal might be able to feel pain. And we’ll come back to what each of these criteria are specifically, but to start: why these eight criteria?

Meghan Barrett: These are actually criteria that are building on previously conducted work. So if you look at some of the work in the 1990s that people were doing on vertebrates, and what criteria they thought were relevant for vertebrate sentience, these criteria build off of those criteria. And really what I would say is one of the major differences that this team that created this invertebrate sentience framework — Jonathan Birch ‘s team, with Andrew Crump as the lead author on that publication, in their report for the UK government and the followup publication — these eight criteria in that framework that they chose are sort of expanded versions of the previously used vertebrate pieces of evidence.

So I’ll give one example of that. In many of the prior frameworks, the piece that’s on analgesics and endogenous neurotransmitters that have analgesic-like effects specified opiates. It had to be opiates, the chemical that was performing that function, because in people, we have endogenous opioids that perform that function for us. And in mammals, they also have endogenous opioids that do that.

Luisa Rodriguez: In other words, mammals have their own internal ability to provide opiates that kill pain in the body when something bad happens to them.

Meghan Barrett: Exactly. That help modulate that response, that pain response. Now, insects do not have the same kinds of endogenous opioids. They, in fact, do not have opioid receptors, which we will talk about later, but they do have endogenous neurotransmitters, things like GABA agonists and stuff like that that actually perform very similar functions. So one of the updates to this framework is to expand beyond opioids specifically to anything that performs that function: an endogenous neurotransmitter capable of modulating a response to pain internally.

Luisa Rodriguez: Nice.

Meghan Barrett: Doesn’t have to be opioids. Could be a different chemical. So that expands on it to make it functional instead of chemical as a definition. So this framework is actually rooted very much in the history of how we’ve thought about gathering evidence for sentience in other groups of animals like vertebrates. It’s just expanding things to be more inclusive and focused on functions, rather than focused on specific nervous system features.

And I think this can be really important to actually do — to focus on function where we can — because we’ve seen multiple times in the history of animal sentience where we’ve focused on the wrong thing. Like, we would focus on the specific region of a mammal brain and then say birds couldn’t possibly be sentient because they don’t have that region. And then it turns out birds just have a different region that does the same function. And we’re like, well, that was a mistake. So focusing on the function instead of the named region or the named chemical, because we know that these kinds of things are multiply realisable, is really important.

Luisa Rodriguez: Cool. That makes sense. And also, if I understood correctly, you and your coauthors didn’t look for other negative emotional states, like fear or hunger or coldness or loneliness or boredom — which I can understand from a limiting scope perspective. Is that the only reason? Was it kind of to make it more manageable?

Meghan Barrett: Some of it was to make it more manageable. That’s also why we only picked these six orders as well. There are other orders of insects, not just these six — many, many others — but we were trying to pick the ones that are the best studied as a way to kind of limit the scope of our review, because I think we already included over 350 studies in this paper. It was an extensive review of the literature. So imagine if we’d also included other kinds of states beyond just potential for pain.

The other thing I would say is that pain is super morally relevant.

Luisa Rodriguez: Yes, absolutely. It does seem like pain is probably very, very relevant to who is a moral patient.

And then zooming out, how much do we even know about how pain works? Because that also feels very important to me. Are we like, “We know how pain works, and we’re just trying to find those types of systems in these insect groups”? Or are we like, “We don’t know what’s going on, but we’re making some guesses”?

Meghan Barrett: I mean, it’s somewhere in the middle, right? I think it depends on the context of pain, and what kind of pain you’re talking about, and whether you’re talking just about basic nociception-linked pain — like, “I touch a hot stove”-type pain — or if you’re talking about things like chronic pain, where we have much more difficult understanding of those problems than we do of things like “I’ve touched a hot stove” that are a little more basic. I don’t claim to be a human pain researcher; it is a huge field with tremendous amounts of research ongoing. I would say if we had solved the problems with pain and we knew exactly how it worked, we might not have so many difficulties treating it.

So I would say we know some things, but there’s a lot left to discover about how pain works, even in humans. When we move to any nonhuman animal, we face the problem where there’s no ability to self-report the subjective state of the being. So what we end up looking for are objective proxies of the subjective state , and then trying to figure out, first, what should those proxies be? And then, as we build the case, what’s a sufficient level of evidence that we feel confident in saying that this is probably a sentient organism, and therefore we should give it some kind of moral status and we should treat it accordingly?

Luisa Rodriguez: Cool. Yeah, that makes sense.

Nociceptors [01:00:02]

Luisa Rodriguez: OK, let’s dive in and try to understand a few of these criteria one at a time — though we’re actually going to focus on a subset, which is the criteria that you in particular are more of an expert on. So the first is: does the given insect have nociceptors? So actually, just to start, can you remind us what nociceptors are?

Meghan Barrett: Yeah. Nociceptors are these specialised cells of our nervous system that are responsible for detecting any kind of noxious stimuli in our environment, and then helping communicate to the rest of our nervous system that we should probably respond to that noxious stimuli. So these are typically cells that have free nerve endings that are right under our epidermis — or for insects, they’re right under the cuticle layer in their epidermis. They also have free nerve endings for insects as well, in their morphology. And those free nerve endings are so that they kind of have a broad profile: they’re reaching out among the surface to kind of a large area for a nerve cell, a large area to detect anything that happens in that area, and then send a signal to the rest of the nervous system accordingly.

Luisa Rodriguez: OK, and do all the insects you looked at have nociceptors?

Meghan Barrett: This is a very challenging question. There’s two parts to this. The first is that the nociceptor itself is that specialised cell that I mentioned. One way you can look for nociceptors is to look for, in the genes of an animal, nociceptive ion channels : these are specific proteins embedded in the membrane of that cell that respond specifically to specific noxious stimuli. So we’ve got ones that respond to heat, and ones that respond to chemicals, and ones that respond to mechanical stress and things like that.

We have done very little work on the insect peripheral nervous system looking for nociceptors. We’ve looked in a species of caterpillar larvae and Drosophila melanogaster larvae are the two species that we have characterised nociceptor-like cells that appear to be functionally nociceptors in their epidermis. We just haven’t looked in the rest. There’s 5.5 million of them. We’ve got a lot to do.

So I can’t tell you definitively that they do have those cells, but I will tell you two other key pieces of information. We’ve done some searching on nociceptive ion channels in the genes of genomes of insects, and these genes are probably a pretty good indicator of a likelihood of having nociceptors in the periphery.

My lab was recently funded by Rethink Priorities to conduct a suite of empirical projects related to insect sentience and welfare. And one of those is a paper that recently came out from my research group with support from a fantastic set of colleagues, Jay Goldberg and Keating Godfrey. Basically, we’re interested in mantids specifically because mantids have served as a source of debate — because of their cannibalistic mating behaviours — whether or not they’re capable of nociception. And this is an old argument from this paper from the 1980s that we were interested in addressing.

So we did a mantid genome, and then looked in that genome for a couple of different nociceptive ion channels [hereafter, “nociceptors”]. We looked at a couple of what are called TRP channels , which are these nociceptors that are actually homologous to mammalian nociceptors: very similar genetically, is what that means. So we looked at thermal, mechanical, and chemical nociceptors, both TRP channels, and we also looked at some ion channels that have a role in cold nociception as well.

We found that many insects, broadly distributed, appear to have at least one copy of most of these genes. There are kind of missing nociceptive ion channels scattered about the insects, the decapods, the arthropods generally, but none of them showed up as all zeros. So for example, of the seven that we are publishing on, Tenodera sinensis , which is the mantid species we studied, is only missing one of them, and then it has up to five copies of two of the other ones. Now, these additional copies can actually potentially perform different functions. You have to do functional [and anatomical] analysis to follow up on this genetic evidence, just to be clear. But this is suggestive of these ion channels being in these species, and thus them having nociceptors.

So I think what I would say is pretty clear is that these homologous, very ancestral, nociceptive ion channels are broadly distributed across the insects. The ones that we’ve looked at have those ion channels in functional nociceptors. And because the nervous system biology, on a very basic level, is very similar across the insects, it is reasonable to expect that you would find that type of cell in other orders of insects, besides just the two that we have officially confirmed have them.

Luisa Rodriguez: OK, so it sounds like there is imperfect but reasonably strong evidence that at least some, and probably many, insects have nociceptors?

Meghan Barrett: Yes.

Luisa Rodriguez: So that fundamentally is what nociception is. And in some studies of insects, we have found both genetic and functional evidence that these channels exist, that these kind of noxious stimuli notification systems exist?

Meghan Barrett: Yes. Genetic, functional, and in some cases even we know that they’re embedded in those morphologically nociceptor-like nerve cells. So we know they functionally work, which we’re able to confirm actually, sometimes outside of the animal. Like, we can take that gene, embed it in another system and then test whether it works there, in other cells.

Luisa Rodriguez: Oh, cool.

Meghan Barrett: So we have genetic evidence, we have functional evidence, and we have evidence — specifically in things like Drosophila fruit fly larvae — that it’s in those free nerve ending multidendritic neurons.

Luisa Rodriguez: Cool. And I’m finding it tempting to just be like, well, that’s evidence that these insects feel pain. But why are nociceptors alone not sufficient evidence for the ability to feel pain?

Meghan Barrett: Great question. We can think about this actually in the human context, which might be most easy for everyone to understand. So I keep saying, imagine you touch a hot stove. The cells in your fingertips, the nociceptors in your fingertips, are going to recognise that heat, and they’re going to change. So your nociceptors are going to send that signal to your spinal cord. And your spinal cord wants to make you pulling away happen as fast as possible. So it sends a signal back down to your motor neurons, and your motor neurons can pull your hand away in a reflex response before you even feel the pain.

So most of us know that we can jerk our hand away from a hot stove before we actually feel anything at all. And we’re interested in that feeling, right? We’re interested in pain — not that nocifensive reflex response that your spinal cord is capable of mediating entirely without any experience of pain at all. Now, at the same time, your spinal cord is sending a signal up to your brain to be like, go get the burn gel. This hurts. But because we know those are two different things — the nocifensive reflex response and the feeling of pain itself in the brain — we have to be very careful if we think that just the peripheral nervous system evidence is enough. We should really be looking for the integration of that information at a higher level in the nervous system, not just at the periphery.

Luisa Rodriguez: This feels like it’s really making a lot of things click for me. So it could just be a reflex, and it’s possible that some organisms are avoiding noxious stimuli just by having these reflexes. But some organisms decide to process the actual feeling of pain. Or they don’t decide, unfortunately, it just happens.

Meghan Barrett: They have evolved to be able to process.

Luisa Rodriguez: Yes, thank you. They do process things as pain, and that has benefits. It also has costs. But the benefits are things like, I can know to go get the burn gel. And so to the extent that a reflex is good enough to avoid most of the noxious stimuli, and evolution has allowed insects to thrive without actually having that specific experience of pain, maybe it’s all just reflexes. But to the extent that evolution pushed insects toward having the pain response, which might allow other fitness benefits, then we would expect them to feel pain.

So I guess that’s where a bunch of the other criteria come in. They’ll point at whether there’s this more complicated pain experience going on?

Meghan Barrett: Right. And that’s why we look for these cumulative cases with multiple proxies, right? No one piece of evidence alone, any of these pieces of evidence — the nociceptors, but also the things we’ll talk about later — no one piece of evidence alone is enough here to say, “For sure, this is the definitive piece. Now we know.” If we had that, we would have solved the hard problem of consciousness , and this would be a nonissue. So anybody who finds that evidence, phenomenal job. But we’re not there yet.

Luisa Rodriguez: Nobel Prize.

Meghan Barrett: Exactly. Instead, we’re at this level where we’re saying, let’s accumulate large amounts of evidence. And the more evidence we have that points in a particular direction, the more certain we can be that this organism is or isn’t having the experience of pain.

Integrated nociception [01:08:39]

Luisa Rodriguez: Great. OK, so a related thing is integrated nociception. What exactly is that?

Meghan Barrett: So like I was just saying, that requirement for pain experience is that the activation of the nociceptor actually leads to that signal being integrated in your brain, right? Not just having that reflex response mediated by your spinal cord — or if you’re an insect, your ventral nerve cord.

So what that means is that we both need to look for evidence of sensory integration in the brain — so the animal needs to have some kind of sensory integrative regions dedicated for that kind of function in its brain — and we need to know that the nociceptive information can actually make it to those sensory integrative brain regions. Like, imagine if it always stops at the ventral nerve cord, and there’s never a signal when I touch that hot stove that goes to my brain, then we might think, even though she has sensory integrative brain regions and she has nociceptors, they’re not connected, so maybe this is a nonissue. So integrated nociception is about both of those things being true.

Luisa Rodriguez: Great, that makes sense. To what extent do we find evidence of integrated nociception in the insects that you looked at?

Meghan Barrett: Again, this is another case of imperfect evidence, which you’re going to hear me say over and over again. Especially for the juveniles. Oh, my goodness. We do not study juvenile insects enough at all.

On the one hand, we have a tonne of great data on sensory integration writ large in insects. We have studied a lot of sensory integration from the visual perspective and the olfactory perspective particularly in insects. The sensory integrative brain regions that are most important for insects are the mushroom bodies and the central complex and the lateral horn.

So the mushroom bodies are this region of the brain that are associated with things like learning and memory, and obviously sensory integration. And for a long time, since the 19th century, they’ve been considered sort of the seat of insect intelligence, if you will allow me to use that term. Very air quotes. And we see mushroom bodies present in all insects except this one group that nobody knows about, so I won’t bother going into details, but one group doesn’t have them . Saying that they all have them is about as close as we can get to a unifying feature, because then they all vary in structure and volume and the types and numbers of cells that they have, and the connections that those cells make with other cells in the brain. So they’re super variable , but they’re a common feature of insect neurobiology.

Another site is that central complex I mentioned. So this is a region of neuropils in the middle of the brain. The mushroom bodies are located kind of at the top, and then the central complex is located in the middle. And this is primarily responsible for sensory integration associated with things like spatial navigation or controlling locomotion, although it’s also been shown to have roles in things like the perception of noxious stimuli, which I’ll talk about in a minute, and even some memory functions .

So basically, we know those two regions — and a little bit the lateral horn , although it’s much less talked about — are responsible for sensory integration of a variety of senses .

Then we get to the question of, OK, they have the integration centre, they have the nociceptors: do they have connections between them? And that’s where things start to fall apart from an evidentiary perspective, because we just haven’t looked for that complete pathway in most groups of insects. The two groups that people have looked at, I would say, are the Blattodea , which are your cockroaches and termites, and then your Diptera , which are your flies.

And I want to note that these two groups are not closely related, so we should think about the development of this characteristic evolutionarily. If we saw two really closely related orders that had it, then we might be like, well, maybe it just evolved in that one little clade, right? But our Blattodea , our cockroaches, are actually hemimetabolous — like I mentioned earlier, that incomplete metamorphosis strategy — and our flies are holometabolous. So they’re on the other side of that big evolutionary divide.

So this suggests that this actually could be a pretty ancestral feature of nervous system organisation. And indeed, we might almost expect that, because we know that every other sensory system [in the insects] seems to make it to those sensory integrative brain regions. It would be weird if the only one that didn’t make it from the periphery is nociception. But I can’t definitively map it for you in all of these insects. And so that’s why we have “no research found” for a lot of the orders in the paper.

Luisa Rodriguez: But if you were to put money on it, it sounds like you would put money on probably them having it?

Meghan Barrett: I am extremely risk averse, and I would probably bet on the vast majority of orders having this at the adult life stage. Much less confident about the juvenile life stage.

But because we see a lot of structural conservation of basic nervous system features, and because we see so many other sensory systems going through the ventral nerve cord and making it to those sensory integrative brain regions, and because we see that insects are able to do learning and memory across orders using noxious stimuli — information which suggests that it’s making it to the brain from a behavioural perspective — all of that makes me feel reasonably confident that all we haven’t done is map it.

Meghan Barrett: So even though I’m not a betting kind, to be perfectly honest — I’m super risk averse, people would tell you — I would probably place some money on this being a pretty broadly distributed feature of insect nervous system organisation.

I wanted to give just one specific example of when we have actually mapped it, and what that sort of looks like to us, just to get a little bit more into the exact neurobiology of insects. You can imagine that insects have a neck, basically, that attaches their body to their head, so they have an ascending nervous system pathway that’s going from the body to the brain, and then they have a descending nervous system pathway from the brain to the body. We have this too. And it’s important to have both of these, because that’s how information gets to the brain, and then how the brain controls your motor function and stuff like that in a goal-directed manner, is through your descending nervous system.

So what we can do, for example, and has been done in the cockroach, is we can actually take readings from the ascending nervous system and say, is that system being activated as we apply certain signals to parts of the body? And we can do the same on the descending side if we choose to. For example, this one really great study by Emanuel and Libersat in 2019 , they basically applied non-noxious tactile stimuli — so just like touching a bug, but it’s not painful or expected to be painful — and then noxious heat stimuli to the abdomens of these cockroaches.

What they found, recording that neck connective, the ascending activity, is that it shows a really weak response to that touch stimuli, but a very strong, persistent response to that noxious heat stimuli. So we know that stimuli is sending some kind of signal to the brain, and the signal is different from just being touched in an innocuous way. So that’s really relevant data, I think.

The other thing that’s really interesting about the research that they did is… So there’s some research that shows that headless insects, just like headless animals of the vertebrate kind, can actually sometimes perform reflexive responses to noxious stimuli. So what they did was cut the heads off of these insects and see if they responded in the same way to the noxious stimuli as when they were fully intact.

Luisa Rodriguez: Cool.

Meghan Barrett: And they found as soon as you either cut that… Well, yeah, cool.

Luisa Rodriguez: I know. As soon as I said it, I was like, oh, grim.

Meghan Barrett: Cool if you’re not the cockroach, that’s for sure. Really interesting scientifically, we can say that. And definitely a good study design. We can also say that.

So the headless cockroaches were unable to mount a full escape response to the noxious stimuli. They could only do this kind of startle reflex that the ventral nerve cord type nervous system is capable of doing on its own. So clearly something important is happening in the brains of these cockroaches to exert descending control over their behaviours in response to this noxious heat stimulus. And this should, again, just be taken as some evidence that these signals are making it to the brain, and that it’s important that they make it to the brain for the fitness of the animal.

Luisa Rodriguez: Fascinating. Another 1,000 facts in the last half hour.

Response to analgesia [01:16:17]

Luisa Rodriguez: Another criterion is response to analgesia, which is a compound that relieves pain. So researchers have done experiments where insects are given anaesthetics or analgesics — like opioids, drugs that reduce anxiety, and even antidepressants. And we’ve also looked at whether insects have internal or endogenous compounds that have potentially pain-relieving effects, in that they change an insect’s behaviour in the same way they might in a mammal.

What do we know from these kinds of studies? Did most insects seem to respond to analgesics?

Meghan Barrett: Yeah, great question. So this story is particularly fascinating to me because if you read this old paper from the 1980s on insect pain , one of the things that it says is, “Insects respond to opioids, but here’s why we shouldn’t take that as strong evidence for insect pain.”

And so people were doing a lot of pharmacological studies in the 1970s and 1980s, exposing insects to opioids and seeing that it appeared to have antinociceptive [effects] on their behaviours. Once we got molecular tools available to us, we started doing genomes of insects and looking for opioid receptor genes in insects, and we found that they actually don’t have them. So insects don’t have opioid receptors at all.

And so that should give us a big question mark, actually, on what’s happening with that opioid data, that pharmacological data. Even though to this day, studies are still demonstrating — like, one just came out in 2023 that we’ll talk about probably in a little bit, because it’s a great example of analgesics in insects – strong antinociceptive responses across a large number of taxa in response to various opioids.

Now, what this probably means, mechanistically, is that there’s some off-target receptor that they bind to that still has maybe a similar function — but until that mechanism is mapped out, I don’t know what to say.

Luisa Rodriguez: We just don’t know what’s going on. Just on that last point, what would it mean for there to be an off-target receptor that it’s binding to?

Meghan Barrett: Great question. So the receptors are what the opioid interacts with; that’s a protein on the surface of a cell that the opioid is going to bind to to mediate that antinociceptive response in the animal. And typically, we see specific receptors are affected by specific signalling molecules. So a molecule has a target receptor for its effects in a particular cell type. But sometimes a molecule is a good fit for a receptor that isn’t its typical target and it might bind to that. So that’s what we call an “off-target receptor.”

Insects don’t have opioid receptors, which is what we would expect to be the target of opioids. But they may have receptors that are similar enough in their structure that opioids can still bind and that can cause some kind of downstream effect in the animal, depending on what the receptor itself is.

Luisa Rodriguez: Cool. Is there a read of this evidence that you find plausible, like maybe the opioid is paralysing them or some other thing that makes it look like it has a painkilling response, but is actually just not that?

Meghan Barrett: It’s possible there could be locomotor confounds. It’s definitely not paralysing, but it’s possible that it could just reduce activity or something like that.

And I should note that we’re really straying far from my area of expertise here, because I don’t research analgesics or opioids personally, but my best bet is that they have receptors that mediate antinociceptive effects, and those are the off-target receptors that the opioids might be binding to — because it doesn’t appear that it’s a locomotory confound, and it has pretty significant antinociceptive effects across both a variety of contexts and a variety of study organisms. It’s still really just a guess. There’s a lot more research that’s needed to say for sure.

So for that piece of it, I bring up that example first with the opioids because that’s the evidence we used to look for in vertebrates: nocifensive responses that are affected by opioids. So why aren’t we just using that same opioid data in insects? This is why. We can’t yet interpret precisely what that data actually means.

But we can look at other examples of other sorts of pain relievers, because we know from vertebrates that opioids aren’t the only thing that can relieve pain. We don’t typically take opioids when we have a headache, for example. So we know there are other kinds of pain-relieving substances out there that we can look at. What do those say? Well, it turns out a lot of insect responses to these compounds suggest really consistent mechanisms, to some degree, with mammals.

This really great study just came out about this: Jang et al., 2023 . It’s fruit fly adults. I mentioned earlier that we have all these genetic tools in Drosophila , and one of the things you can do is you can edit their genomes to express new genes. Basically, imagine that we’re expressing a human nociceptive ion channel: so we know this is a nociceptive ion channel with a particular function in people, and we’re using that person gene — not the fly gene that’s homologous, but the actual person gene — and we insert that into the fly genome. That means it’s going to be expressed in their tissues, and that resulting protein, which is the ion channel, can function in the flies just like it does in the humans.

This is what they’ve done to these flies in this study: they’ve given them this human capsaicin-activated TRP channel, this nociceptive ion channel. And then they give them food that is capsaicin food, like really spicy food. Imagine it being given food, but that food is like just ghost peppers all the time. So what do they do naturally before you give them the analgesic, and then what do they do when they have analgesic?

It turns out that these [transgenic] flies, when they start trying to eat that food, they immediately stop eating it as soon as their mouthparts touch it. And then they start trying to groom their mouth parts off, very specifically, and then they’ll actually starve themselves to death over eating the food, even though it is nutritionally complete.

Luisa Rodriguez: Oh, wow.

Meghan Barrett: Because each time they go to eat it, they will try to clean their mouthparts off. Now, if you give them a variety of different types of analgesics — so you can give them ones that target that ascending pathway we discussed, or ones that target the descending pathway. There are certain analgesics that target one versus the other; you can give them either type. So they gave them things like opioids, but they also gave them NSAIDS, they gave them GABA agonists and things like that, which I mentioned are analgesics earlier for insects.

They gave them those types of chemicals and found that in all those cases, it would actually rescue survival. So the insects would be willing to consume enough food to be able to survive when they were given analgesic, despite the food being capsaicin laden and them having these capsaicin receptors in their mouthparts.

So they suggest in this particular study, and I think it’s good to just sometimes read the original words of the authors, because I’m not a pain biologist, and so I just want to be really clear that I’m insect neuroscientist; I know a lot about insects, but I don’t consider myself to be a mammalian pain biologist by any stretch of the imagination. So I often am interested in what the researchers who do these studies and are pain biologists have to say about how close these things between mammals and insects actually are.

So here’s from the abstract of that study. It says:

Our results suggest Drosophila to possess intricate pain sensitization and modulation mechanisms similar to mammals, and we propose that this simple, non-invasive feeding assay has utility for high-throughput evaluation and screening of analgesic compounds.

Luisa Rodriguez: Wow.

Meghan Barrett: So I think in their own words, and I do want to be very cautious here, that sometimes people loosely use the word “pain” when they actually mean “nociception” — so I don’t want to overstate the authors’ confidence in that distinction, but I will just say that the mechanisms appear to these authors to be similar to the mechanisms in mammals. Enough so that we can use Drosophila as a system to test for looking for analgesics.

Luisa Rodriguez: Wow. Yep. That’s super compelling. Though really, really sad. Like really sad.

Meghan Barrett: Welcome to my life now. It’s like, how many sad studies can I read? From a scientific perspective, this is fascinating. And from an evidentiary perspective, this is a really crucial piece of evidence that I find very compelling. And so I’m glad that somebody has done this work, which is of course how science has to progress. On the other hand, of course you’re sitting there and you’re thinking, well now we’ve developed these mutant flies with this high-throughput assay.

Luisa Rodriguez: That will starve to death rather than eat hot peppers.

Meghan Barrett: Yeah. And I think this is also compelling: remember that evidence we talked about earlier, where people said that insects don’t respond in typical ways to pain, and they’ll keep eating even though they’ve had their abdomen cut off? They won’t keep eating if they have these capsaicin receptors. So that suggests that there’s something going on with goal-directed behaviour and motivational states that we should take seriously in some contexts.

Luisa Rodriguez: OK, so part of me is like, painkillers seem to totally work on insects. That’s a very reasonable read of the evidence, as far as I can tell. Another part of me is like, could this somehow still be a reflex, or just like a non-pain process? Like, could the fruit fly be getting some signal that is like, “This thing is worth avoiding; don’t eat any more of it” — that doesn’t feel like pain, but is more robotic or something? Do you think that’s possible, or is that just too inconsistent with what we know about evolutionary history and the way these ion channels probably work?

Meghan Barrett: I definitely think that’s possible. And I think that’s part of why the cumulative approach to the evidence is so important. None of these pieces of evidence can be seen as like the magic piece of evidence required to feel convinced. Instead, what we’re looking for is: the more things that are similar between this organism and organisms that we’re sure feel pain, and the more reason we have to suspect that the same kinds of selective pressures might have been acting on these organisms to have them produce similar kinds of mechanisms, and the more similar their mechanisms are and their physiology is in response to these kinds of stimuli — well, now we’re starting to build a case that says there’s enough evidence that these things are similar, that maybe we should take seriously the possibility that this isn’t a reflex response, and it is actually producing pain. So it’s really about that cumulative case approach, which I think is really important.

Analgesia preference [01:25:57]

Luisa Rodriguez: OK, let’s move on to another one. So a very related criterion is analgesia preference, which basically means an animal shows that they value analgesics like painkillers, either by administering a natural painkiller internally, or by seeking a painkiller out in the environment — or, I guess, by prioritising accessing it in the environment over things like food or water. To what extent do insects show this preference? Because this feels like very important evidence to me.

Meghan Barrett: Yeah. This is criterion eight of the framework. And I think for many people, they would find this to be the piece of evidence they would most strongly weight. So each of these criteria doesn’t have to be weighted the same, even though there’s eight of them, which is something that lots of people have talked about in the use of this framework.

Anyway, this is criterion eight. And what I will tell you is that we have such a paucity of data on this that it’s very difficult to talk about. There has been one study conducted on this in insects at all to date. I know some people who are working on conducting studies now on this, but to date, we have one study to go off of. So I’ll tell you a little bit about that study and what we should and shouldn’t take from it, I think.

So this is a study in honeybees. It’s work done by Groening et al., 2017 . They basically are taking honeybees, they’re anaesthetizing them, and then while they’re anaesthetised, they’re cutting one of their legs off, or putting a clip on one of their legs that’s exerting some potentially painful pressure. Then they let the bees wake up, and they provide them with two feeders: one that is just sucrose and water, which bees like sucrose, and then one that is sucrose water and morphine. And they see whether or not the ones that have been injured are drinking more from the morphine-laced feeder than the ones that are not injured are drinking from the morphine-laced feeder. And what they find is that there’s no preference for the morphine-laced feeder in the injured bees compared to the uninjured bees. So this suggests there is no analgesia preference in that particular case.

OK, so that’s the one study that we have. It does not suggest that insects are able to do analgesia preference. However, there are many things we might critique about this study, and I think those are important things to mention in context for why we might not want to place too much confidence in this single piece of evidence.

The first is: we’ve already mentioned insects don’t have opioid receptors. Picking morphine as your analgesia for the study over something like a GABA agonist, where we actually do understand the mechanism… It’s just not what I would pick, because we don’t know for sure what it actually does and we don’t know how it’s doing it. So that would be my first critique, is like, let’s pick an analgesic we have more confidence in for insects specifically.

My second critique would be that insects can taste morphine, and we know it tastes bitter to them. So the problem is if your delivery mechanism is a drinking-based mechanism, you are now asking an insect if it prefers a bitter-tasting substance over a sweet sucrose solution after it has been injured. It may not prefer that. So it is not an equal comparison between the two feeders of the experience that they’re having drinking from it, which is what you would ideally want in this context.

The next piece of critique that I would give is that the insects were not trained to associate any possible effects of the morphine with drinking from that feeder. They were just given access to them simultaneously. Now, we expect that drinking morphine doesn’t lead to an instantaneous response in the body, right? There is some kind of delay.

So let’s imagine a bee is injured. It wakes up, it’s like, “Ouch, my leg really hurts.” It goes over to the first feeder that it sees and it starts to drink from that feeder, and it’s like, “Yuck, this tastes terrible. I’m not drinking from this feeder.” It goes over to the other feeder, starts drinking from that one and it’s like, “Oh, this is pretty great.” And as it’s drinking from that feeder, the effects of the morphine start to hit, if there’s effects at all. Now the bee has learned to associate the other feeder with the effects of the morphine, not the morphine feeder.

So typically when you do these kinds of studies in animals, you train them to associate the effects of the analgesic you’re giving them with whatever the substance is that you’re providing them to drink. When you present them simultaneously, you actually haven’t taught the animal what stimulus it needs to seek out to be able to get the pain-relieving effect. So you could imagine totally random results from this.

The last thing I’ll say that I think is interesting is that the bees were under anaesthetic when the injury was delivered. And then they woke up and were given the opportunity to seek something. And this makes some sense, because again, there’s trauma that could be associated with doing the procedure and just stress associated with doing the procedure. And you don’t want to assess stress; you want to assess response to injury.

But you can imagine, again, the insect injury can clot very quickly — and we don’t know whether or not there’s actually pain from injury when the injury happens in insects or after the injury has clotted in insects. Both of these time points are unknown to us right now. So we’re assessing something we’re not sure is painful, with a substance that we’re not sure is pain relieving, in a way where we haven’t trained the animal to know that this is a pain-relieving substance with that stimulus. I don’t see this as particularly compelling evidence against insects being able to fulfil criterion eight, but I don’t have any evidence that they do either.

Luisa Rodriguez: OK. So that does seem like weak evidence in either direction at best, and it sounds like that’s all we know. So we basically don’t have much information at all on this maybe pretty important criterion. So yeah, noted that that is a weakness.

Meghan Barrett: For sure.

Flexible self-protective behaviour [01:31:19]

Luisa Rodriguez: Another criterion is flexible self-protective behaviour. And first, I have a guess at what that means, but can you spell it out?

Meghan Barrett: Yeah. This is basically a behaviour that we can reasonably expect will be protective in response to an injury of specifically that body part. So not just like increased grooming of the whole body in response to being injured, but increased grooming of specifically the area that was injured. So flexible in response to the timeline of injury or something like that, and then directed specifically at that site.

Luisa Rodriguez: And what does the evidence say on this with respect to insects?

Meghan Barrett: This is, I think, a fascinating one, in part because we have so many examples of them not engaging in this behaviour in all contexts and cases, as we’ve discussed before, but we do have some examples that appear to suggest that in other contexts and cases, they may be able to do this kind of behaviour.

So there’s some evidence of wound-tending behaviour in moth larvae. Manduca sexta is a common model species, and basically they give them an injury in a particular abdominal segment, and then they see increased wound tending and strike responses towards that abdominal segment. It’s anecdotal, so I don’t want to make too much of it, but I just want to note that that’s some of the evidence.

There’s also a study from the 1980s where they gave an abdominal puncture wound to cockroaches and found that they groom specifically that side and area of their abdomen much more. So it increases both general grooming — like they groom themselves generally more — but also specifically that area. Which, given that one of the major concerns for insects that experience a cuticular breach is the pathogen problem, where they are much more likely to get diseases if there’s an open part of their surface, you can imagine that both general grooming and specific grooming of the site might be valuable for them from a fitness perspective.

Luisa Rodriguez: Yeah, I was going to ask what the mechanism was. And I’m still curious, does insect grooming actually reduce pathogens?

Luisa Rodriguez: I don’t know. That doesn’t seem like something I can do by grooming myself.

Meghan Barrett: So we live in comparatively such a sterile environment for pathogens and predators compared to ancestral humans. So think about monkeys picking mites off of each other’s backs. Grooming to get rid of pathogens and parasites is actually reasonably common across the animal kingdom. We just don’t tend to get as many mites these days, or fleas or lice or whatever. So yes, of course there’s both the microbial level, like the really small stuff — and for that it’s like hand washing and stuff like that.

Luisa Rodriguez: Yeah. Great. And how sceptical should we be as a result of just the fact that this evidence is super mixed?

Meghan Barrett: I think it’s context dependent. I think that’s one thing that’s really important about it. And also I’d love to see more data presented on the prevalence of these different behaviours. So maybe I see one cockroach out of 30 groom that site-specific wound. That’s actually much less strong evidence than if all 30 of them do it, or if 29 out of 30 of them do it. I want more data like that.

Right now, almost all the data on both sides is anecdotal. [Note: since recording, a new study has come out with non-anecdotal evidence in favour of site-specific self-protective behaviour in response to heat injury in bumblebees.] It’s like, “I saw a locust do this,” “I saw an ant do that” — and none of this is all that helpful for me in terms of weighting these pools of evidence against one another. I need more information, and I need people to specifically test this question, because a lot of these anecdotes are reported in the pursuit of other research. Like we’re testing something else, and we see this, and then we report on it. That is not as helpful to me as somebody actually specifically testing this question.

I also should note there’s some interesting evidence that came out recently where somebody has been testing this in ants. They’re testing allogrooming — which is ants grooming other ants, not ants grooming themselves, which is a very important difference for this evidence being useful from a pain perspective. But I just want to note that it shows us how important grooming can be for the fitness of the animals in response to injury. There’s something like an 80% difference in survival for ants in the wild that get their wounds groomed or don’t get their wounds groomed by their nestmates. That shows us just how many pathogens there are in the environment, and how important it is for insects to be able to recognise the site of an injury and groom it if they’re able to do that.

So pain might be very relevant for that reason, at least for long enough for them to be able to groom that wound. [Note: since recording, a new study has come out that shows that ants are the only species other than humans to amputate legs of wounded conspecifics in order to reduce rates of lethal infections.]

I have one other point I’ll say on this very briefly, which is just remember that Jang study that I talked about and the grooming of the mouthparts? I think that’s really interesting and compelling evidence that we see site-specific grooming. Very cool anecdotally reported evidence. Would love to see somebody study this specifically, but I think that’s interesting.

There’s also been some research on crickets in the ’90s . They were interested in what stops male crickets from engaging in courtship behaviours. And they gave shocks and heat stimuli and also gave some strong pinches to the epiphalus, which is [part of the] the male reproductive organ. And they found that the insects would groom the epiphalus and stop mating also in those particular cases, when a strong enough pinch was delivered, even when no fluid leaked out of the body cavity as a result. So when you see the fluid leak out, now you have a confound, because maybe they’re grooming to get that fluid off of the body part they want to use. But when you don’t see that fluid leakage, and you just have the pinch delivered to that body part and they’re still grooming it, that suggests something else might be going on.

Luisa Rodriguez: OK. And again, grooming feels like my brain can tell a story for how that would be reflexive. Do we have reason to think that it’s pain motivated?

Meghan Barrett: We definitely have reasons to think it could be reflexive. I mean, again, each of these criteria you can explain as a reflex mechanism, and people did that in dogs for centuries. People were like, “These dogs are just little reflex machines. When I vivisect them and they make loud noises, it’s just their body having a reflex.” That’s Descartes: he was very convinced that vertebrate mammals that were not humans did not have minds like we have minds, and did not feel pain the way we feel pain. So again, I think it’s a question of accumulating a large enough number of objective proxies with similar enough mechanisms that we should start to be worried.

And I worry that we are often interested in explaining things as a reflex, and that is one simple explanation. But another simple explanation is all of these things are showing up mechanistically similarly and induce similar fitness-relevant behaviours, and have underlyingly similar neurobiological structures to some degree. At what point do we say the simplest explanation is that probably this is producing a similar kind of experience?

There are two ways to cut that simplicity question. One thing I think we often do is we think, if the insects are sentient, then too much of life is sentient. I mean, that’s everybody, right? That’s all of life, if the insects are sentient. But we’re forgetting how much other life there is out there that is succeeding without — we think — being sentient. The vast majority of species and individual organisms out there in the world do not even have nervous systems at all. Bacteria make up the vast majority, we believe at this time, the best evidence suggests. Although I will tell you, the microbiologists are having a conversation about what it even means to be a species. So don’t come at me, microbiologists. I know it’s complicated.

So including insects in our group of organisms that might plausibly be sentient doesn’t actually expand, in terms of our whole conception of life, that much who makes the cut. We are missing, from our view, a large portion of who is alive.

Motivational tradeoffs and associative learning [01:38:45]

Luisa Rodriguez: Yeah, I hear that. I’m very tempted to dig into it more, but for the sake of time, let’s talk about our last two criteria. Both are behavioural and not your area of expertise. One is motivational tradeoffs, the other is associative learning. Briefly, can you explain what motivational tradeoffs are?

Meghan Barrett: So in this paper we were looking specifically for nociceptive motivational tradeoffs. This is anytime there’s two competing motivations modulating the nociceptive response. For example, the organism needs to acquire food and to do that, it needs to cross some nociceptive barrier — like a shock barrier or something like that. And these tradeoffs tend to indicate that pain is more flexible or context dependent, and thus might occur in the brain. That’s the idea. Especially if the two stimuli are not presented simultaneously and so they rely on memory or something like that for the animal to be able to make that tradeoff, it suggests there’s some internal common currency that the animal is using that might be affective states.

Luisa Rodriguez: That makes sense. And to what extent did the insects you looked into here display some of those?

Meghan Barrett: Very little evidence on this one as well. Several of the behavioural criteria just haven’t been studied that much in insects, adults or juveniles. There have been a couple of studies in fruit fly adults and a study in bumblebee adults that we can look at. Generally what they suggest is that they may be able to perform these tradeoffs using memory instead of just simultaneous presentation of stimuli, and also with these tradeoffs being somewhat graded. So like, if you change the sucrose concentration from 10% to 40%, you might get different responses from the animal. So it’s not just like sucrose at all versus pain, it’s sucrose of a particular concentration versus pain. But I would say that a lot more research here is required for sure.

Luisa Rodriguez: We’re not finding insects that clearly don’t do this; we’re just finding very few studies on the question at all.

Meghan Barrett: Exactly.

Luisa Rodriguez: Then let’s move to the next one: associative learning. This is just where an animal learns to associate some noxious stimuli, like an electric shock, with a neutral stimuli, like a smell. What’s the story for why associative learning is thought to be indicative of capacity for pain?

Meghan Barrett: So the adaptive value of this is thought to be something like, if you can learn from an aversive experience, it allows you to avoid that experience in the future, right? You touch that hot stove, you learn to avoid touching the hot stove, because you have associated touching this thing with the pain. Now, you are better prepared to not touch the other hot stoves that you come across in your life. And your fitness, in theory, improves, and you pass on more of your genetic information to the future generations, and they are more successful and so on and so forth. So evolution selects over time for organisms that are capable to do this kind of associative learning.

So we look at all the evidence for associative learning, from the most basic to the most complex we could find in insects. The more complex types are generally considered to be better evidence for sentience and conscious awareness. So even though we document, and most of the studies that have been done have documented, classical conditioning all over the insects, we also looked for evidence of those more complex forms that might provide better evidence.

Luisa Rodriguez: OK, nice. And what broadly did the evidence say?

Meghan Barrett: First of all, basically associative learning is super widespread in insects; this is super common. Nobody’s surprised by that who studies insects. In the adults, we know they do associative learning. Their mushroom bodies are super important for it. NBD.

But what about those more complex forms of associative learning? That seems more interesting to us. So things like trace conditioning: trace conditioning is this idea that you can provide a time interval between your two stimuli instead of having them overlap, which is delay conditioning. They’re both forms of classical conditioning: in delay conditioning, the stimuli overlaps, you’re presenting them simultaneously; the other one, you’re having a delay, a time interval between them. It’s confusing to me that the one that is called delay conditioning does not have the delay in it.

So trace conditioning requires subjects to keep track of that delay between the two stimuli. And there’s some idea that this requires conscious awareness of the stimuli and also the interval of delay. What’s really interesting here is that insects can actually be faster than vertebrates at this kind of learning. And several studies have demonstrated [insects are capable of delay conditioning] in the fruit flies, both looking at odour-related paradigms, but then also paradigms that are using visual information.

And we find in both of those paradigms that flies can learn, even with these trace intervals — although they don’t seem to learn the duration of the interval, from at least that particular study. So there’s some evidence that they’re capable of doing trace conditioning, although again, more research outside of just fruit flies would be needed. And also figuring out more about whether they can learn that interval would be good.

Results [01:43:31]

Luisa Rodriguez: Yes, so many questions, but for the sake of time and for the sake of ending the suspense that everybody has been feeling at this point: after all of this research, which insect orders would you bet on feeling pain? Maybe I shouldn’t phrase it that way either.

Meghan Barrett: I guess what I could answer is the question of which insects do we have the strongest evidence for the plausibility of their pain experience? How about that? So which ones am I more confident in, based on the accumulation of evidence using this framework?

First of all: adults definitely more than juveniles, because we have so little information, so little data to go off of on the juveniles, and their nervous systems, especially in the holometabolous, complete metamorphosing ones, are under development. So there’s reasons to think that especially early instars might not be as capable of things like even basic sensory integration, potentially. So adults more than juveniles, for sure.

That said, when we look at the orders that we researched: the Blattodea (which is our cockroaches and our termites) and our Diptera (which are our flies and mosquitoes) pop out as having met six of eight criteria. The original study done by Jonathan Birch’s group showed that decapod crustaceans meet five of eight criteria. And cephalopods, your octopuses, meet seven of eight criteria to the same level of confidence. So these guys are right in between your decapods and your cephalopods, in terms of accumulation of evidence at the adult life stage. And for the remaining two criteria for those groups, we just don’t have any research at all — not a single study to point us in one direction or the other. So obviously we should fill in those evidence gaps quickly.

But I would say the reason those two pop out is just because they contain model species. The fruit fly in the Diptera is studied for all kinds of things, and the American cockroach has been a pretty good study system for nociceptive neurobiology for a long time as well. So they pop out not necessarily because they are actually more likely to be sentient than the other orders, but just because they’re studied more frequently for these kinds of characteristics.

Luisa Rodriguez: Oh, how annoying to go through all of that effort and then to have the end result reflect more about the research done on insects and which insects are valuable to human researchers must be really frustrating.

Meghan Barrett: Yeah, although not too surprising. Once we got that result, I was like, of course, this makes total sense — because this question has been really understudied in this group, and this group is so diverse that of course the research on this topic has almost happened by accident in service of other human goals in these particular model species.

I think what was surprising to me was that the bees, ants, and wasps — which I mean, hymenopteran bias showing over here as a person who studied bees, ants, and wasps — but I tend to think of them as really cool and really complex and socially sophisticated, cognitively sophisticated. So I would have expected that they would just [fulfil the most criteria] in this framework.

Luisa Rodriguez: Really shine.

Meghan Barrett: Yeah, really shine. And I think what that shows us is that they aren’t studied as much on the affective dimension, more on the cognitive dimension. So yes, they are extremely cognitively sophisticated, and people have studied a lot about their behaviours and their cognition, but they haven’t studied as much about their capacity for things like pain. And so that really demonstrates to us that cognition and pain are not at all the same thing. They can relate to each other, but they’re not the same, and they have to be studied independently for that reason.

Luisa Rodriguez: OK, so that’s the high-level takeaway. Tonnes more research needed. But also for me personally, more research pointing in the direction of insects being at least more likely than I would have thought to have the experience of pain. Yeah, people should research this.

Reasons to be sceptical [01:47:18]

Luisa Rodriguez: To try to put my sceptical hat on, I’m going to try to generate some reasons why you might not think this evidence is as compelling. For one, none of the insects definitively failed any of the criteria, which feels a little bit surprising and maybe even suspicious. Does it feel that way to you?

Meghan Barrett: It could. I think I’ll say two things about that. One is that mammals don’t seem to fail definitively any of the criteria, but we don’t find that suspicious that when we look across the mammals, none of them seem to definitively fail any of these eight. Instead, we find that to be good, strong evidence that they’re capable of doing the thing. So I think there’s something to be said for that.

Luisa Rodriguez: Anti-insect bias is showing.

Meghan Barrett: Yeah, there’s this intuitive sense, like, they shouldn’t be able to do all eight of these. Isn’t it suspicious that they’re doing so many of them? Maybe your criteria are terrible.

Luisa Rodriguez: Yeah, I’m just deciding the quality of their criteria based on the result.

Meghan Barrett: And lots of people have that view. And even I would say to myself to some extent, had that response of like, well, how good are these criteria then? And part of what convinced me on that was looking at the older vertebrate frameworks and seeing that they’re essentially relying on similar things. And then thinking more about these proxies and saying, are there other proxies I would add? Not necessarily.

I do think, and if we had a whole other podcast episode we could do, I and many other people have critiques of this framework. I do not think it is perfect. I have many thoughts on ways it could be improved. I’m writing a paper about that, writing all these papers that will come out this year that you may find interesting if you like this podcast episode. You know, lots of people have written about how this could be improved. The original article was published in Animal Sentience and a bunch of people responded to it, and then the authors responded to that [which you can see in the “Article thread” section of that link]. There’s been great dialogue on the way this framework could be improved.

But broadly, I think for me, this framework is great for determining when we should be cautious and take something seriously. The evidence is certainly good enough for that bar. In no way am I claiming it’s a definitive bar. It’s not like if you meet all eight, you’re absolutely sentient. But if you meet six of eight, we have enough evidence that we should start really considering this problem, researching this problem, taking the moral status of these animals seriously for now, until we have better information. So that’s one thing.

Luisa Rodriguez: Yes, especially given the number of them.

Meghan Barrett: Oh yeah, a lot of them. The second thing I’ll say is that although nobody definitively fails it, I actually think we do get close to a definitive failure in one juvenile case that we were looking at, but I couldn’t prove it because we are lacking some information at this time. So early-instar honeybee larvae — like the first, second, third instar — they go through six instars, and in the first [two] of them, 3.0.CO;2-Q”>they do not appear to have a developed mushroom body or a developed central complex, and this would suggest that they fail sensory integration in the brain proper.

However, I couldn’t find convincing evidence on what was going on with their lateral horn, which is the other, third centre I didn’t spend much time talking about. And there’s always the possibility that sensory integration that is relevant occurs in other areas of the brain. We actually know there’s sensory integration that occurs in the general protocerebral mass, which is the rest of the brain tissue I didn’t talk about. So I didn’t feel convinced by that evidence that they for sure fail it. But you will notice that they’re rated lower than many of the other ones are for that reason. Their mushroom bodies start to develop in the [third] instar.

Now, one thing that’s interesting is that just because honeybees fail it doesn’t mean that all bees and Hymenoptera fail it at early instars, or that other insects fail it at early instars that are holometabolous. Remember, our hemimetabolous insects already have their mushroom bodies from that first instar. So they’re already in on having sensory integration, even from a very early stage. For other holometabolous insects, we actually do see that they have one or the other of those regions from an early instar as well.

Beetles, for example, many species have prolegs, which are these little tiny, not official legs that they have in the larval stage. And they do that so they can move around much more easily. Things like caterpillars and beetles want to be able to move around in many cases. Things like honeybee larvae have no need to go anywhere while they’re developing. They just hang out in the cell, in the hive. So those ones [the beetles or caterpillars] that have those prolegs actually have some development of their central complex, which is that navigation centre that I mentioned that does sensory integration in their first instar.

And this makes some sense. They’ve got to navigate. Honeybee larvae do not need to navigate. They hang out where they are. They have many fewer of what we call action-selection opportunities. So you might imagine, actually, that for organisms that are more independent at the juvenile life stage — like caterpillars that are eating plants in the wild, or beetles that need to move around as larvae — they may have more developed sensory integration centres earlier than things like honeybees that literally just hang out and get fed by adults until they end up pupating and emerging.

So one thing we could consider looking more into is tracking species that have and don’t have these action-selection opportunities during development, and seeing if that changes when certain parts of their nervous system develop and come online. But that’s as close as we get to failure with the evidence we currently have.

Luisa Rodriguez: OK, so it sounds like at least some sensible pushback on this objection. One that I feel weighing more heavily for me is that it seems like a lot about how much I care about this problem just kind of rides on the degree to which an animal experiences a thing painfully. And maybe again this is just size bias, where I’m like, it’s a tiny bug, maybe that means it feels tiny pain, but it does seem like we at least would want to know something about the severity, the capacity for severe pain, and if it were less severe, that would seem less bad.

Do we have any sense of whether, if insects are feeling pain, there’s reason to think it’s severe or not?

Meghan Barrett: This would be another Nobel Prize–winning question to answer. I will say that the closest we’ve gotten to answering it is theoretical, not empirical. So we’ve sort of delineated what the options are theoretically, but we don’t have any evidence right now to support any of those particular outcomes in a strong way.

Probably the most in-depth treatment you can find of this question is in this book that’s coming out this year called Weighing Animal Welfare by my colleague Bob Fischer . There’s actually a chapter that’s dedicated to the kinds of cognitive processes that we think could influence the degree or severity of pain in different animals. One thing that’s challenging, though, and that chapter really explores in depth, is that you could imagine ways that a capacity could both increase or decrease the severity of pain for an animal.

Like, imagine [mental] time travel. So in some ways you could imagine that [mental] time travel could make your pain more severe because you’re remembering previous times you were in pain, and you know how long the pain is going to last, and so that makes you feel even worse. Or you could imagine, you know how long the pain is going to last. You know it’s temporary. So even though it really hurts, you know it’s going to be over, and that makes it hurt less for you than for an animal that doesn’t have [mental] time travel, and is just stuck in the present moment of that pain for as long as it lasts.

The other piece of theory that I think is compelling to me is this idea of would it be beneficial, from an evolutionary perspective, for an organism to have tiny pains? Like, what is the point of a pain? The point of a pain is to motivate you very strongly against an extremely fitness-relevant experience. Would it be relevant to be just a little motivated to avoid those kinds of things? Or should we expect these animals to be really motivated to avoid these things?

The last thing I think from the tininess perspective is just to recall that point we discussed earlier about having more neurons. It’s not like each neuron creates the experience of pain for me. So it’s not like three of my neurons have fired, so I’m having a three-neuron pain as compared to 300, I’m having a 100x type of pain. Instead, it’s just like with the visual system and things like that, where having more neurons doesn’t necessarily mean you have more discrete pictures; it might just mean you have better resolution or a more complicated experience to some degree somehow. So it might just be more about repeating modules than it is about creating a bigger experience. And I think that’s something we’ll have to figure out as well. But just being tiny probably doesn’t provide us reason to think that they might have tiny experiences.

Luisa Rodriguez: Yeah. I mean, I’m a complete non-expert, I’m an anti-expert. I am beyond naive about this. Could it be that… I can imagine lots of pain being terrible for fitness, like we could feel in theory much more pain, but that might paralyse us, keep us from doing things that might help us. And it seems like lots of insects might live in very dangerous environments. And it seems at least possible to me that there are so many life-threatening stimuli that feeling extremely intense pain about all the dangerous things is not actually evolutionarily fit as a strategy. But I don’t really know where that’s coming from, so I’m just curious if you have a reaction.

Meghan Barrett: This is interesting. Yeah, let’s explore this a little bit. I think the first thing that comes to mind for me is that you’re right. When an organism is in an environment that is constantly exposing it to noxious stimuli, we do often see changes in the nociceptive neurobiology of that species.

A great example comes up in the mammals, where we look at naked mole-rats. They live in these subterranean burrows, and because there’s a bunch of them, because they’re eusocial mammals, they’re constantly engaged in respiration, so they’re releasing CO2 into their environment. And that CO2 gets trapped underground with them in their burrows, because there’s nowhere for it to go, because there’s soil all around. So that can actually lead to tissue acidosis of their exterior surface.

What they’ve found is that in naked mole-rats , they actually lack responsiveness to tissue acidosis in the periphery. They’ve evolved this mechanism, neurobiologically, that blocks signalling to the brain from the ion channels that are sensitive to tissue acidosis. We might ask, why is that? Well, from a fitness perspective, it’s probably not that great for a naked mole-rat to just be walking around all day constantly in pain due to some kind of damage, when its whole environment is necessarily going to cause that kind of damage. So it’s evolved something different than mice and rats, its close mammalian relatives, in its ability to experience pain — because it’s not fitness-relevant for naked mole-rats to be sensing their environment as constantly harmful.

So we might imagine too that if we see insects that are adapted to live in super hot environments, they might not have thermal nociception at all, or they might have thermal nociceptors with a much higher activation threshold than the ones that insects in other environments might have. Certainly we could expect to see something like that, and I think that’s very plausible. Then it’s just what are the environments the animals are living in, and which kinds of nociception might they have lost or not lost? Because we don’t say naked mole-rats don’t feel pain just because they can’t feel that pain, right? They can feel other pains just fine. They feel thermal pain, mechanical pain just fine. So it’s just this one thing, but they still have the capacity for other kinds of pain.

I would push back a little bit on whether or not insects live in environments that are necessarily more dangerous than for mammals and things like that.

Luisa Rodriguez: Yeah, as soon as I said it, I was like, it seems kind of similar to, I don’t know what it’s like to be a gazelle. Or at least it could be, doesn’t seem crazy.

Meghan Barrett: I think for predator insects it’s like being a predator, and for prey insects it’s like being prey, and for scavengers it’s like being a scavenger. Their worlds are just a little smaller in some ways and happening more rapidly in some ways. But yeah, it’s just a different scale of living. I’m not sure it’s necessarily more dangerous.

Luisa Rodriguez: I guess if I’m trying to probe at what I actually believe here, it seems like, yes, there is some pain that would probably be so much that it would be evolutionarily unfit. And also there is probably some amount of pain that is probably too little to motivate something to do anything. And maybe that just means that evolution will push toward a certain experience of pain that is moderate: enough to motivate behaviour, but not so much to have a bunch of costs. So maybe we should actually expect it to converge in some sense onto something that’s unpleasant in the way pain is for me, but also not that often totally excruciating, because that would be terrible and costly.

Meghan Barrett: Disadvantageous.

Luisa Rodriguez: Does anything like that sound plausible to you?

Meghan Barrett: I think that sounds roughly plausible, yeah. I mean, I think in our daily lives, excruciating pain… Even if we imagine not the really fancy lives we live these days, even in the less fancy lives we lived in our evolutionary history, excruciating pain does not seem to be a daily occurrence. And that makes some sense, right? That would be a really potentially fitness-damaging thing. And we see that in chronic pain situations now, for people who do have excruciating pain day in and day out because of something being wrong with their nervous systems’ biology: it is very fitness-problematic for those individuals. They do not have the same ability to function the way they might like to because of that chronic pain problem. So I think that’s right. Excruciating pains are reserved for extenuating circumstances.

And let’s not forget also the endogenous neuromodulation system, where even when we have pains that are excruciating, we have these internal mechanisms for helping us modulate that pain in response to other motivational states. So I’m sure that cutting your own arm off is excruciating, and that’s why I keep going back to that. I mean, it just seems horrible to me. It seems like it should be excruciating. The fact that anybody has successfully done that to save their own life is wild to me, but that’s part of what our nervous system has for us: both the ability to give us excruciating pains and the ability to modulate those pains so that if we have other motivations we need to take care of, we can.

Luisa Rodriguez: Yeah, it’s interesting. I have the intuition that both of those abilities are pretty complex, and therefore might require more complex neurological structures to actually allow for them, but it also seems plausible to me that it’s so important to both feel pain in life-threatening circumstances, and to modulate it to balance other competing needs, that maybe they’re just abilities that evolved super early on because it they’re so valuable?

Meghan Barrett: These are all good intuitions to explore, though, because I don’t think that you’re alone in having these kinds of intuitions — where on the one hand, this seems really complex, on the other hand, maybe it’s really simple. And yeah, the answer is like, we really just don’t know a lot of this. There’s a question of the difference between having a capacity and the complexity of the capacity and the degree of the capacity and the kinds of the capacity. We could imagine variation along all those axes, but still having the basic capacity be a very simple thing that evolved very early. And then what we get after that is the explosion in degree or kind or number of neuromodulation systems. That kind of complexity could come later; the basic capacity could be much earlier in the evolutionary history.

To come back to evolution — because we love to come back to the idea that sentience and pain evolved — this is also really important to think about, because if we’re going to be sceptical about sentience, we need to be sceptical about its evolutionary history, not just which organisms it’s in today. So we shouldn’t just be looking at the presence/absence of key features in this particular animal. We should be saying, where is this animal in the evolutionary tree? Who else am I confident is sentient? What does that mean about the likelihood this animal shares those features?

And there are two possible hypotheses you could entertain here. One is the idea that sentience evolved exactly one time, and so everybody descended from that common ancestor, unless maybe they lost it for some reason, has that characteristic. So if you accept both vertebrates and any of the inverts — so a cephalopod or a decapod — if you’re convinced on a single invertebrate and you also are convinced on a single origin point for this, you have a problem, right? Because the closest common ancestor to all of those folks is very far back.

And so you’re going to have all your insects, all your nematodes, all your decapods, all your annelids (which are another kind of worm) included, if you believe that there’s one common ancestor and no loss events. Now, maybe you think there’s loss events, but now you’re talking about multiple loss events, because there’s so many invertebrates. So you’re going to have to justify each of those losses, which you could potentially do.

Another possible hypothesis is that sentience evolved multiple times independently in different groups. I would probably say this is more plausible in my view, in part because we see multiple emergence of things all the time in evolutionary history.

Vision is a great example : we know that eyes might have evolved as many as 40 times during animal evolutionary history. And then, when we think about the development of eyes, it’s crucial to consider how they all generate the same basic function of being able to see something, even though they may vary in a lot of ways structurally.

For instance, we saw the multiple emergence of what we call these crystalline lenses in the eyes of animals: some were made from co-opting calcite, others were made by co-opting heat shock proteins, still others were made by co-opting other novel proteins. All of them make these crystalline lenses, right? Or you could consider that independent but convergent evolution of similar structures in vertebrate eyes and spider eyes — and that can result in, again, the same basic capacity to see something.

Of course, then we can talk about how the exact functions of seeing using these different structures or similar structures can vary. You know, acuity can vary, or wavelengths that the animal can sense can vary. But still, we think that same basic capacity of some kind of sight is there for all of these animals.

This is all to say that it makes it more complicated if we’re looking for something like consciousness. So the function we’re interested in is consciousness instead of vision. Now we’re saying that if there’s more than one origin point, we need to be looking for potentially divergent structures capable of producing that common basic function. And of course, that common basic function can have lots of variance and gradation. And we don’t even have a good grasp yet on human consciousness , so you can see how acknowledging the possibility of multiple independent origins would then make this all very challenging to figure out.

But in any case, I think when you look at this from an evolutionary perspective, it’s important to consider who’s a close relative? Who are your common ancestors for that group? When you think these characteristics evolved, why do you think they evolved there? And then, if you’re somebody who takes crustaceans seriously, given that their close relation is the insects, you’re going to need to seriously consider the hexapods too.

Luisa Rodriguez: OK, so if I really try to generate reasons to be sceptical — because I think this just is an important enough topic that we should look at all the reasons to be sceptical — what about the fact that at least some insects are known as r-strategists ? This is in contrast to K-strategists: r-strategists are species who have lots and lots of young, and who don’t invest that much in those young, so many of them die before they reach adulthood — but some of them survive, and because of the low investment, that’s an evolutionarily successful strategy in some cases. Whereas K-strategists have very few offspring, and then they invest a lot in them and basically try really hard to make sure as many of their young get to adulthood as possible.

I can imagine that because the r selection strategy involves lots and lots of young dying very, very young from starvation and predation and probably other things that the evolutionary pull to experience pain really intensely is weaker — because it’s actually just less important that those young survive to adulthood. Does that make sense?

Meghan Barrett: This is also a good question. I feel like my thoughts on this are still developing, so I don’t know if I have as solid of an answer on this one as I want to. But I guess I have a couple of loose thoughts.

The first is that r and K selection are relative phenomena in some sense. For example, cats and dogs are r strategists compared to people. But obviously they are K strategists compared to most insects. Most insects are r strategists compared to people, but K strategists compared to bacteria, so on and so forth. So I think it’s important to keep that in mind. And again, keep in mind the fact that that means that the vast majority of life is more r strategists than insects are. Like in the scheme of all of life, they’re technically kind of K strategists, if we’re considering bacteria as important. So that’s the first thing I’d say.

The second thing I’d say is that I don’t know how… The way you phrased it was something like, it matters less that each individual survive because there’s so many of them. But evolution is acting on these individuals, right? At the level of being an individual, I don’t actually necessarily care… I mean, there’s indirect fitness benefits of your siblings surviving, but my direct fitness benefits are based on me surviving, not my siblings surviving. So I want to pass on my own genome, not my brother’s genome, to the largest extent I can from an evolutionary perspective.

(I’m saying “want” here, and what I mean is that of course “it should be selected for” that I pass on as much of my own direct genome as I can. But we’re using some colloquial language for clarity, otherwise it gets really dense.)

So what that means is that for that individual, it doesn’t matter that their parents’ DNA is surviving by all of these other offspring that their parents had. They would still, preferentially, from an evolutionary perspective, pass on their own genetic code, is my sense. And so I would say that I don’t know that there’s any reason to suspect that having large numbers of offspring reduces the selective pressure on any particular individual, and thus that individual’s experience of its world.

Luisa Rodriguez: OK, that feels compelling to me. I don’t feel like I know enough about this topic to be like, yes, that is a foolproof response, but it makes sense to me.

Meghan Barrett: I don’t think it’s a foolproof response, and this is one of those areas that I have been thinking about, and I would love to talk more with an evolutionary biologist about, because I also don’t consider myself to be an evolutionary biologist. I know about evolution the same basic way most entomologists are aware of evolution and think it’s important for our work. But I’m not an evolutionary biologist by training, and so there’s many things about evolution, I’m sure, that I am not an expert on, that could inform my thinking here.

And I have several in-progress pieces of work that I’m trying to tease apart — things like that multiple-emergence hypothesis I mentioned earlier versus the single-origin hypothesis and more — because I think evolution is a really missing part of this argument and debate. But I think it’s essential that we’d be putting things in an evolutionary framework. And your question is an important one, and I think probably an evolutionary biologist would inform both of us more about whether or not what I’ve said is plausible.

Luisa Rodriguez: OK, so evolutionary biologists should reach out to Meghan Barrett.

Meghan Barrett: Yes. If you’re an evolutionary biologist listening to this, come at me. I want to hear from you. What did I say wrong? Tell me.

Luisa Rodriguez: Nice. Excellent.

Meghan’s probability of sentience in insects [02:10:20]

Luisa Rodriguez: So to really put you on the spot, we’ve talked about all this evidence, and you’ve said that there is some strong evidence for potentially some insects having the capacity for pain. But I’m curious, is that like you were at 0.01% that maybe fruit flies have the capacity for pain, and now you’re at 1%? Or did you go from 10% to 50%? What exactly are your beliefs?

Meghan Barrett: I get this question very frequently from people who are like, “What is your specific numerical probability of sentience estimate?” And then I’ll say things like, you know, there’s so many insect species, how could I? I’ll try to demure a little bit on it, and then eventually I’ll just be like, I’m not giving you a p(sentience). I’m sorry to have to be so direct.

So I will say this to you also: I’m not giving you a p(sentience). The reason I am not giving you a p(sentience) is, one, I think the error bars are so large right now that it’s almost a meaningless number. Because I’m waiting on so much evidence. So much evidence. And so I think that’s really an essential feature of it for me.

The second thing is that I worry, especially as an expert, that that number would be overemphasised. And there’s actually a great post about this from someone else, Jason Schukraft, who has researched this, and he has something that he’s written about why he also has refused to give people, in many cases, a sentience score. This is a number that somebody would inevitably put into a spreadsheet, and they would use that spreadsheet to make all kinds of decisions. And that number does not reflect the complexity that you and I have now spent three hours discussing, and barely scratched the surface of, right? I want to talk about the complexity and the nuance, and a number does not demonstrate that.

I think it’s important also that we understand that if you have updated at all towards insects plausibly being sentient, scale takes the rest of the issue for you to a serious place. There are so, so, so many of them that if you take it seriously at all, then you need to be thinking that this is an issue to work on. There’s been some great work on interspecific tradeoffs and comparisons and moral weights, led by Bob Fischer , with some input by Jason Schukraft and others summed up in that Weighing Animal Welfare book. There’s a whole sequence about it you can also read on EA Forum: a lot of great research went into that, both theoretically and empirically.

And the thing that it suggests to me when I read through it, and I think also the team would probably stand behind me saying this, is that insects are worth taking seriously; if you take them seriously at all from a sentience perspective, scale carries you the rest of the way.

Luisa Rodriguez: Yeah, this is actually a good place to mention that two of our recent podcast episodes are super relevant here.

One is my interview with Jeff Sebo , where we talk about what he calls “the rebugnant conclusion” — which is the conclusion that the sheer number of insects means that we should probably take super seriously the idea that insect welfare might be a really, really pressing problem, even if we only have very low credences on insects feeling pain.

And then another super relevant episode that just came out is with Bob Fischer , and that’s on how to compare the moral weight of humans, specific insects, but also other species, given the empirical evidence we have about each being sentient.

So if listeners are interested in learning more about these arguments from a more philosophical perspective, I really recommend those.

One thing I do want to try to clarify a little bit for people, because I worry that a listener could just as easily say something like, “Meghan Barrett seems to think that it’s extremely likely, like overwhelmingly likely, that insects are sentient” — but I also think a listener could come away thinking, “Meghan Barrett puts slightly higher than the average person out there in the world probability on insects being sentient.” Is there something that you feel comfortable saying, like, “More likely than not,” or, “Less likely than not, but higher than I thought five years ago”?

Meghan Barrett: Well, definitely that last one is true. Definitely higher than I thought five years ago.

I guess what I’ll say in response to that is that I think it’s likely enough that I’ve changed my whole career based on it. I was an insect neuroscientist and physiologist by training. I was researching climate change-related topics and the thermal physiology of insects, and I was researching how insect brains change in response to the cognitive demands of their environment or allometric constraints associated with their body size. And I was doing that quite successfully and having a lovely time. And I find these questions really scientifically interesting. I have, if you look at my CV, probably somewhere to the tune of 15 to 20 publications on just those two topics alone from my graduate degree days and my postdoctoral work.

And I was convinced enough by my review of this evidence to switch almost entirely away from thermal physiology and very much away from neuroscience — although I do still retain a neuroscience piece of my research programme — to work on insects farmed as food and feed, and their welfare concerns, and trying to make changes to the way that we use and manage these animals that improve their welfare. So I now have a bunch of publications about welfare.

I’ll also say that many of my colleagues have been extremely open and pleasant about this conversation, but also some have been more challenging. And I don’t mean to say that in a negative way. I’m very understanding of the practical reasons why this conversation is uncomfortable for our field. There’s regulations that could come into effect that would be very challenging for many of us who research insects to deal with on a practical level. So I’m obviously sensitive to that as a researcher myself.

But also, because, you know, I’ve heated insects to death, poisoned insects to death, starved insects to death, dehydrated insects to death, ground up insects to death — I’m sure I’m missing something that I’ve done to an insect at some point in my research career — but it’s uncomfortable now, the research that I do, reflecting on the research that I have done. And I can imagine others may feel judged by bringing up the topic, and thus feel defensive instead of exploring the current state of the theory and the research with an open mind. I think a lot of humility is necessary too, given all the uncertainty that we’ve talked about here. And that can be really uncomfortable and really humbling to be confronted with such a morally important unknown.

So I try very hard to really take everyone’s concerns seriously — all the way from the rights-focused folks through the hardcore physiology “I’m going to research my bugs any way I want to” folks. I think it’s really important to try and bridge as much of the community of people who care about this topic one way or the other as possible with my own very divergent experiences.

But I would just say that it hasn’t always been low cost in some cases. Personally, it hasn’t been low cost: it’s been a hard personal transition for me to make, and to continue to be in this career with the way that I see the evidence falling out so far. And it’s been, in some cases, professionally hard.

So I’m convinced enough for that. And I think that’s something worth taking seriously. You know, I’m that convinced that I’m changing my own career, yes. But I’m also not so convinced that I think it’s 100% certain. I live constantly with professional and personal uncertainty on this topic. So I’m convinced enough to make major changes, but you’re not going to see me say insects are sentient, that I’m sure of any order or species that they are sentient. There’s a lot more evidence that I hope to collect, and that I need to see collected by the scientific community, and a lot more theoretical work that needs to be done before I am convinced one way or the other.

Luisa Rodriguez: Yeah, that sounds really hard, and I don’t envy you. I have tried to work on problems kind of like this before, where the bulk of the probability was on the thing not being a problem at all. And I found it really hard and demotivating.

But logically, it seems like the scale of the problem is really unfathomable and the evidence seems at least strong enough. And again, listeners can go back to our episode with Jeff Sebo , where he talks about the kinds of credences you need to have: they’re not very high for this to become a truly massive, massive global priority.

Views of the broader entomologist community [02:18:18]

Luisa Rodriguez: I’m actually curious what the broader entomologist community thinks about insect capacity for pain?

Meghan Barrett: We could spend a long time on this question. I’ll try not to. [Note: since recording, Meghan has released a preprint on a survey she conducted of entomologists’ attitudes toward and knowledge of insect welfare.]

So this has been a question that has been of concern to entomologists for over a century. And actually, you can go all the way back if you want to to Darwin, he has a little book on emotions from animals to man, and he writes about insects in that book. I’m not going to get the quote exactly right, but it’s something like, “Even the insects have jealousy, rage, fear.” OK, Darwin, whatever. So he doesn’t present any compelling evidence for that, just to be clear. It’s just Darwin saying some Darwin stuff. Sometimes you call it on evolution and not on other things.

Luisa Rodriguez: Yeah, some hits and misses there.

Meghan Barrett: Yeah, some hits and misses there, Darwin. I’m not convinced on Darwin’s evidence for that case, but just to demonstrate that it’s been of concern to people for a while.

So then I think when we get into the early 20th century, there was a really strong push against anthropomorphism in kind of all of animal sciences, vertebrates and invertebrates — where a lot of natural historians were writing in this very beautiful but often quite anthropomorphic language, where they are describing insects in very people-like ways. And there was a push that that was not objective, and was kind of interfering with us doing good, rigorous science. And again, somewhat true, although there’s also some reasons why too much pushback against anthropomorphism can sometimes also be problematic for how we frame and understand things in science. So balance is often key.

So then in that early 20th century period, we see a lot of, “Kind of, we don’t really know, but we think, we’re pretty sure not…” And a lot of it is based on what we’ve discussed with mechanical responses or responses to mechanical injury, where people are taking pictures of ants without their abdomens , eating, and saying, like, this just doesn’t look like an organism that’s in pain. Very reasonably, they’re saying that.

Then the next kind of key development in the literature happens in the 1980s. This paper comes out called Eisemann et al., 1984 . It’s written by, I believe, a bunch of graduate students — and maybe some faculty advisors, although I’m not sure — in Australia. That’s how I understand the story anyway.

So this paper comes out and basically makes a case against insects being able to feel pain based on neurobiological and behavioural evidence. Similar categories of neurobiological and behavioural evidence that we find in the Birch framework, to be perfectly honest — slightly fewer numbers of categories, but same kinds of categories. And importantly, they do ignore all the heat and shock information, and focus really exclusively on responses to mechanical injury. And there’s a bunch of other flaws in that paper. Also, it’s 40 years old, so, as you might imagine, our understanding of insect nervous systems and behaviours has advanced substantially in the last 40 years.

I have a paper series that I’m working on right now with some other entomologists and philosophers, where we’re actually responding to the Eisemann paper.

Meghan Barrett: Because that paper is obviously out of date, which I think the authors would also agree with at this point: that it needs an update from that perspective. But it has some theoretical flaws, some empirical flaws that should be detailed, because it’s such an influential paper in the field. People still cite it to this day as kind of an authoritative text on the plausibility of insect pain. And we are way beyond the data that’s in that paper, so responding to it seems appropriate.

So that kind of settled the issue for the entomological community for a while. And so there’s been this persistent dogma, even as other evidence has continued to develop over the last couple of decades, that insects don’t have to feel pain. That’s why we’re not regulated. If insects could feel pain, of course we would be regulated, like all of the other groups of animals.

For me, personally, as a graduate student, I took the same ethics and responsible conduct of research course that all the graduate students take. And I think we even made some jokes about how the entomologists had to sit through the vertebrate researcher ethics training, but of course it didn’t apply to us.

And I remember Animal Behavior Society has these student research grants — and Animal Behavior Society, for a while, has been the scientific society that has taken invertebrates most seriously, from an ethics perspective — so this was all the way back in 2019 maybe, when I was applying for one of their student research grants, and they required that I do a little form on the ethical treatment of my insects. My bees. And I was like, “Pffft… ridiculous! Look at all this work they’re making me do that I shouldn’t need to do because insects don’t feel pain.” Yeah. Thank you, Animal Behavior Society. You were on the right track, it turns out, on what I might want to be thinking about.

So I think we’re starting to see — especially in some of the societies that are cross-taxa, where they know what the research is like in vertebrates, and so they understand the strength of the research in invertebrates better, like Animal Behavior — we’re starting to see some movement on this front.

Luisa Rodriguez: Yeah, that actually makes me wonder: you alluded to the fact that as a grad student, you were like, “Why the heck am I in this ethics course? I study insects, and insects don’t suffer.” What changed for you?

Meghan Barrett: What changed for me is that I actually decided to take a look at the evidence. I mean, just to be transparent, before that I had not read a single study about whether or not… I hadn’t even read the Eisemann study about whether or not insects could feel pain. That’s how little reading I’d done. My intuition was entirely based on them being small and on the fact that I did not have to do any ethics reporting, and I knew that other people did. And therefore, obviously scientists must have figured this out, and we knew insects didn’t feel pain, and so we don’t have to do any reporting — and it’s done, it’s settled, it’s over.

So that was my perspective early on in my degree. And we don’t tend to talk about this in entomology labs as part of our training internally either. This was not something that my advisor — or I would say advisors generally, because I don’t want to call out my advisor specifically on this as if he did something wrong — advisors don’t seem to have this conversation with their graduate students in our field. There is actually research on that, that demonstrates in entomology, we are not discussing ethics — whether that’s the ethics of genetic modification or the ethics of how we treat our animals — nearly enough. And graduate students are feeling underprepared. There’s a great study about that, Trout et al., 2010 .

I think what changed then was that I started to look at the evidence. And what prompted me to do that was that I was actually considering for a little while maybe doing an alternative to academia job. You could spend a whole podcast episode talking about the challenges of being an academic . But I was interested in understanding more about alt-ac careers, and I thought, welfare is a lot of physiology and a lot of nervous system and behaviour work. And I don’t do welfare, but I do all those things. So if those are the important components of welfare, then yeah, could be cool to try this out, see how it goes.

And even though in researching welfare, there was no requirement that I look into the evidence for sentience — it was really about the welfare concerns of black soldier flies — of course, as you’re reading about it, it only matters to read about it because of the sentience question. So I was like, I should probably start reading some stuff about sentience and about animal ethics more broadly.

So I read Bob Fischer’s intro to animal ethics book was actually my first introduction to animal ethics. And then I read, like everybody does, some Peter Singer, and blah, blah. But that was the first exposure I ever had as an animal scientist to [an in-depth treatment of] animal ethics was that book. And it was super eye-opening to me how complicated and challenging animal ethics is as a field, not just in research or agriculture, but just all around us, the way our society is structured. Really, really great intro to animal ethics. If you are not familiar, that book is great. I actually have given it to a bunch of entomologists at this point, because I’m like, this is a good introduction for people in our field to animal ethics. It’s just a really fair, competently written, compelling, interesting, well-written book that is good for beginners like me.

Meghan Barrett: So I read that, and then I started reading more into the sentience [question]. What have people considered to be the evidence for sentience in vertebrates? Oh, that’s it? Like the Smith and Boyd framework from 1991 , for example. I was like, “ That’s what it took for us to be convinced? Well, if that’s what it took, we’ve got some problems — because we have that data, in many cases, in insects.”

So I just didn’t realise what the level of evidence was in vertebrates. I just assumed it was much stronger in many ways that it isn’t. And I assumed we had a much better understanding of consciousness than we do. And then, seeing all the uncertainty there too, I was like, well, this is starting to make me very nervous. And yeah, now I’ve been reading about the topic and doing a lot of work on it in my own scholarship for several years now, and all it has done is convinced me to be even more uncertain, the more I read on it.

Luisa Rodriguez: Yeah, that’s a really inspiring narrative. Thanks for sharing.

Insect farming [02:26:52]

Luisa Rodriguez: Let’s move on and talk about one of the practical sides of all of this. So: insect farming. What are insects being farmed for?

Meghan Barrett: So I primarily research insects farmed as food and feed — for human consumption or for vertebrate livestock consumption. So there you’re looking at major species like crickets, yellow mealworms, and black soldier flies — although there are other species like palm weevils and house flies that also fit into that group; they’re just slightly less abundant in terms of numbers farmed.

But I want to specify there are many, many, many, many reasons that we farm insects. For example, the sterile screwworm programme in the United States, which is trying to reduce these parasites and make sure they aren’t moving across this particular border where we’ve been able to stop their progression. And they hurt livestock animals . That programme rears sterile screwworms each year for release. We have a bunch of biocontrol-type programmes like that.

We’ve got integrated pest management, where we’re rearing parasitic wasps for release on farms and things like that. So there’s those kinds of farms. There’s silk farming, farming for dye, farming for producing shellac — like resins and things like that that can come from different species of insects. Obviously, we manage honey bees. You might or might not choose to call that farming; you might choose to call it management. But we farm them for a lot of different applications.

And we’re coming up with new applications too. Like cell-cultured meat, there’s some companies out there that are starting to farm insects to produce some of the proteins required for cell-cultured meat .

Luisa Rodriguez: I had no idea about that last one. So it sounds like probably this industry just touches on loads of other industries. But you said that you focus on insects for feed for agriculture, and also for people?

Meghan Barrett: Yeah. Human consumption and for livestock.

Luisa Rodriguez: Got it. Can you remind me briefly what the scale of the industry is? You’ve already said this, but it was maybe hours ago at this point.

Meghan Barrett: It’s been a while, yeah. So the kind of best estimate we have is from 2020. That year they estimated about 1–1.2 trillion insects across crickets, black soldier flies, yellow mealworms, and other species lumped together. Again, probably a serious underestimate at this point, because the industry is growing so fast, year over year. So we would expect, three years having gone by, that the industry would be much larger. And indeed, the producers that I’ve talked to and mentioned this number to have kind of scoffed and said that’s definitely an underestimate. We’re definitely rearing more than that across the globe at this point. [For example, see this article that claims one producer in France rears 3 trillion insects alone each year.]

Luisa Rodriguez: And then my sense is that this is a growing industry, but I don’t know that much about the rate or how big it’s supposed to get. How is it projected to grow?

Meghan Barrett: I think there are a lot of possible projections for how it will grow. One thing to keep in mind is just like, the amount of additional investment capital that has flowed or gone into this industry over just the last five years, for example. I’m a little uncertain on these precise numbers, but I think it’s something like $25 million going into these companies in 2015, all the way up to like $430 million by 2020 — so really exponential growth.

And there’s a great report that you can read by the World Wildlife Fund and Tesco that looks specifically at the UK context and demonstrates that there is like 20x the demand for how much they’re actually producing. So there’s significant expectation that it’s going to grow in the UK and the EU over that period of time as well, at least according to that report. There’s all kinds of caveats on, will it actually grow this much? What are the real markets for it? There’s regulatory questions where if certain regulations stay in effect or get added, that’s going to change the growth of the industry substantially, or where it’s located substantially. It’s very complicated.

But I guess what I’ll say is, going back to that 2020 report, in it, they look at one of the biggest possible markets for insects as feed — which is expected to be most of the market, because not that many Western nations right now have insects on their list of things people like to eat on the reg, so we’re expecting feed to be a lot of it. Fishmeal replacement is one possible example of a big market segment for this. And the UN has actually estimated we could sustainably replace 100% of fishmeal with insect protein, potentially. Let’s imagine a conservative 25%, of just that market: we’d be looking at 40 to 80 trillion additional insects a year just to replace 25% of fishmeal. That’s not considering any other livestock groups, the pet food market, human consumption — just that.

So when I say there’s tremendous potential, regardless of exactly what projection model you’re looking at, there are a lot of ways that this sector can grow and influence the economy and meet new demands.

Luisa Rodriguez: Got it. I think my brain is doing a bit of the like, ahh, these numbers are too big. I don’t understand them. But the general impression I’m getting is they are very big. There are many, many, many times the number of vertebrates being reared in factory farms. And so to the extent that we’ve moved at all in the direction of insects being sentient, and to the extent that some listeners care about vertebrate factory farms being a bad place, this seems like much, much larger in scale. Maybe much lower in our confidence that these insects are sentient, but like, unclear how those compare. It seems really plausible — and maybe you’ve already done this — that if you were to do some back-of-the-envelope math, insect farming would seem like a really, really, really big problem.

Meghan Barrett: Yeah, I think it depends a lot on your assumptions. But probably the easiest case to make is just: it’s an industry, it affects many individuals — and that makes it important to consider questions about welfare.

Where you go from there as the person you are depends on your moral assumptions. I can’t really speak to everyone’s thinking on that front. My focus as a scientist is just on whether there are welfare issues, and if so, what empirical work needs to be done to address them.

Luisa Rodriguez: Yes. Makes sense. We’re going to come back to what might it be like for these insects on farms, but I still want to try to get a better sense of what to picture here. I’m curious, where does insect farming take place in the world? What kinds of facilities and farms are we talking about?

Meghan Barrett: It’s a super diverse industry. In part, it’s super diverse because, remember, we’re talking about multiple species of insects. So just like you would never say a cow farm and a chicken farm, or a cow farm and a pig farm look the same and are the same in scale and how they operate, of course we would never say a black soldier fly farm, a yellow mealworm farm, and a cricket farm should look the same.

But also there’s just tonnes of variation because it’s a really innovative, rapidly growing industry. It’s just starting to scale up. So we’re just starting to see some of the biggest facilities being built right now. You know, bigger and bigger facilities being built over time.

I think you’ve got everything on your diversity spectrum, from these rural, kind of concrete pens in Thailand, where people are rearing a couple of thousand crickets at a time to sell at their local market, all the way through big automated facilities. There’s this one, for example, that has some great illustrative pictures online — JM Green in China; they’re a black soldier fly rearing facility — you can look into their facilities and see they’ve just got these pallets like five bins high by two deep by four across, or something like that. I can’t exactly remember the number of bins. And each of those bins contains about 10,000 larvae. And then those pallets are just stacked all the way down the greenhouse. [Note: JM Green has since gone out of business and those photos are no longer available online.]

And some of these facilities are really big and there’s less human labour involved. Some of that can be really great from a climate-control perspective, and making sure that the facility is producing similar kinds of products and managing the animals in a similar way.

So really small, all the way up through really big — and even bigger on the horizon.

Luisa Rodriguez: Makes sense. I would expect that as the industry grows, you’re going to get more of these massive insect farms. Is that a reasonable thing to guess?

Meghan Barrett: Well, since we have zero of them right now, definitely we’re going to get more of the massive ones, because we’re building these global-scale facilities for the first time. So definitely we’re going to get bigger ones.

I think we’ll also get many more smaller ones, in part because one of the values of insect farming is potentially being able to reutilise waste streams. And so you might not want to truck that waste all the way, say, across the United States, to your global-scale facility. Instead, you might want to put your smaller black soldier fly unit right next to your waste source if you have a really high-density waste-producing area. So that’s one way to think about it, is that you might get both more smaller ones and also more larger ones. But I think for economy of scale reasons, we are going to see a lot of growth from where we are right now in the industry.

Also note that there’s a lot of really interesting innovation that the industry is doing in generating mobile units. There’s this company called Better Origin in the UK, and they’re interested in kind of democratising the insect-rearing process so that individual farmers who have agricultural waste — like additional plant waste or something like that — can actually rear black soldier flies on their farm in these sort of tractor trailer units that are set up for turning their waste back into protein for their livestock animals. So there’s a lot of innovation happening, and a lot of variation in how people are rearing these animals.

Luisa Rodriguez: OK. And we’re basically going to talk about the ethics of this industry, but it sounds like there are going to be loads of considerations. Like, it seems like a good thing that waste might be processed by these insects in a way that might have environmental benefits, but maybe it seems like a terrible thing if the conditions are bad and we have reason to think that they’re experiencing them as very bad. So we’ll have to tease all of those apart.

But just a little bit more setting the scene: I think you said that the insects most often raised are mealworms, black soldier flies, and crickets. Can you remind me what we think about those particular species and their potential capacity for pain?

Meghan Barrett: Yeah, that’s a great question. Our black soldier flies are in the Diptera , which, if you recall, is the one that has the fruit flies in it, so there’s a lot more evidence there. We saw they met six of eight criteria at the adult life stage — so five of eight for the decapods, seven of eight for the cephalopods: it puts them right between those two groups.

But we should keep in mind that for this particular species, most of them are actually slaughtered at a later larval instar. So we really should, primarily, by the numbers, be interested in juvenile dipteran potential for sentience, not the adults. So what did our framework say there? At later larval instars, we think four of eight to a high or very high degree of confidence. So that’s a little bit less than the decapods: enough to be thinking about it, but certainly not as concerning as the adults.

Also important to note that, in my view, not each of these eight criteria should be equally weighted. But currently, the way the framework is set up, you do equally weight them, because you’re just saying four or six of eight. I think the larvae meet some of the least strong of the eight. And so keep that in mind, too, that this is more than just a number. There’s kind of a complex set of evidence behind it, and it is much weaker for the juveniles.

Luisa Rodriguez: OK, so it’s a weak four out of eight, not a robust four out of eight.

Meghan Barrett: That’s my feeling. I’m sure some people would disagree with me about my weak four, but that’s how I feel: that it’s a weak four for the juveniles and a stronger six for the [adult] flies. Although, again, to me, some of the even stronger pieces of evidence are still missing for insects broadly; they just haven’t been studied, like we talked about.

So then we move on to the yellow mealworms. So those are beetles; they’re in the Coleoptera . Like we’ve said before, for both the Blattodea and the Diptera , which are the ones that come out really, really high in the analysis, it’s because they’re model species that people study nociceptive neurobiology or nocifensive behaviour in. We don’t have any of those species as model species in the Coleoptera or the Orthoptera — which is your crickets, grasshoppers, katydids, locusts, et cetera. So that really hurts them in this analysis, because there’s just basically very little research to go off of.

So for the Coleoptera , for our yellow mealworms, we’re seeing about two criteria being filled at the adult life stage. And again, that’s two of the weaker ones — just basic nociception and sensory integration. And only one at the later larval instar that we have confidence that they fulfil to a very high or high degree. Again, the rest of it is just no research is really being found.

Then for the adult Orthoptera , they’re fulfilling three to a high or very high degree of confidence. And for the nymphs — because they are hemimetabolous, so they don’t have a larval instar; they have a nymph phase instead — they meet two criteria to a high or very high degree of confidence. So much less evidence in those two groups than we had.

Although again, I’ll note that we should really think about sentience from an evolutionary perspective. There’s reasons to think that even though we might not directly have evidence at that time for those orders, if sentience evolved in the ancestor of arthropods, we might expect it to be broadly distributed across many groups.

Luisa Rodriguez: Right. It sounds like some key things to remember here are, one, some of the evidence is weaker than some of the other evidence. And the evidence that we do have for most of these groups — except for the adult flies, et cetera, category — is on the weaker side. Pushing in the other direction, we have things like these are some of the insects that are more understudied, so it’s not for good reason that they’re missing certain criteria.

Meghan Barrett: Right.

Luisa Rodriguez: And also we have this broader thing that’s like, insects are biologically diverse, but also similar in some fundamental ways that would make you think that if we’ve got confidence in flies, et cetera, that that’s some decent evidence that it exists in other types of insects.

Meghan Barrett: It suggests that it could, yeah. For sure. We shouldn’t be confident it doesn’t.

How much to worry about insect farming [02:40:56]

Luisa Rodriguez: Right. OK, so just adding lots of uncertainty as we think about what to do, how to think about this…

Meghan Barrett: That’s my job!

Luisa Rodriguez: Yeah, I’m trying to figure out how to orient to this as a person who cares about how to prioritise different problems in the world. It doesn’t sound like you’re confident insect farming is an abomination — it sounds more like you think it’s something we should think seriously about before scaling it up to really huge levels.

Meghan Barrett: Yeah, I definitely don’t think that you would hear me saying it’s an abomination. I work on insects as food and feed, so I suppose it would be surprising if that were my view.

Like you were alluding to earlier, but we haven’t yet discussed: there are promises and challenges with every industry. So there’s a lot of questions for me about which insects are we rearing, at which life stages, under what conditions, for what goals? Is it feeding into and supporting other animal agricultural practices that we want to support or not support? Or is it replacing them?

Because you can get into the complex topic of interspecific tradeoffs — where, say, somebody was willing to consume insects as their protein source in place of chicken. Well, we know a lot about chicken farming maybe not always being the best. If somebody was willing to replace consuming chickens with some number of insects, there might be a story there about what that interspecific tradeoff looks like as well, that is worth taking seriously.

Then there’s questions about the environmental impacts, where we understand that producing more sustainable protein may improve conditions for wild animals [by reducing habitat loss]. So we might want to take that seriously too, as well as if we can reduce our arable land practices or our pesticide spraying by reclaiming waste substrates instead of farming additional new plant protein. Now we’ve got an insect-versus-insect species tradeoff question, where we can either produce more soy, for example, and hurt a bunch of insects in the production of soy in the wild, or we can reclaim a waste substrate but potentially have lower-welfare rearing conditions on farms.

So I think it’s insanely complicated from an ethical perspective, and also super underexplored by ethicists who are way better than me, just to be clear, at doing these kinds of tradeoffs and comparisons. I am not an ethicist; I’m an entomologist. But I think it’s really complex. And so the question for me often is, in how I want to participate in this dialogue, can I use my skill set and expertise to improve conditions for these animals where I see places that improvements can be made using empirical data?

Luisa Rodriguez: Great. That all sounds just extremely reasonable. Let’s get into some of the specific conditions so that we have a sense of what kinds of maybe painful situations insects might be in, if they are in fact feeling pain. Can you give some examples of the kinds of farming practices that you think might be painful, or I guess otherwise low welfare, for at least some insects that are being farmed?

Meghan Barrett: Yeah, for sure. There’s a couple of publications that I have out on this, and they’re all open access, so anybody can read them and look at them. So there’s one on black soldier flies , one on yellow mealworms , and then one on crickets [in] the Journal of Insects as Food and Feed .

So in those reports, we detail at length what kinds of concerns we see for these insect species. And there are both similar ones and different ones, I want to be clear — because just like with cows and pigs, some things they experience are in common across farming practices, like potentially slaughter issues, whereas, you know, a pig is not a cow; there’s going to be some things that are bad for pigs and pig farms that are not a problem for cows. So we have the same issue with insects.

Inhumane slaughter and disease in insect farms [02:44:45]

Meghan Barrett: Some things that I think are pretty in common across the insects are going to be slaughter. So methods that are employed right now are things like boiling and blanching; grinding and shredding; freezing, potentially in air and liquid nitrogen; we have microwaving; baking in sand; baking in the sun; baking in convection ovens. I think that covers most of the methods currently employed.

And there’s no stunning practices or anaesthetics for insects right now that are used in farms broadly. I will say there is one report of a small-scale cricket producer in the UK who uses CO2 to knock out the crickets before slaughtering them, but that is the only report I’ve seen of that. Certainly it’s not common practice.

So this is an issue for across species. In all three of the papers, we try to delineate less versus more humane from among those categories of slaughter methods as like two general buckets we can put these methods in. Because of course, standard operating procedure is going to affect how quickly those methods occur and how painful they might be, so without being able to account for what standard operating procedures are typical, we can’t actually say for sure this is good, this is bad.

But I think there are some methods that are pretty clearly going to take a long time. For example, microwaving is never going to be instantaneous. And we know that it’s a heat-based method of slaughter, and we know that heat is one of the things that insects seem to respond to. So, unlike things where we might be more confused — because insects don’t respond to colds in ways that are clearly communicating distress all the time; and they don’t respond, like we talked about before, to mechanical injury in ways that are clearly communicating distress all the time; we might have more uncertainty about things like that, just whether they’re actually painful or not — but we’re not as uncertain, I think, in the heat-based case. So methods like baking in convection ovens and microwaves are pretty clearly going to make it into the less humane category.

Luisa Rodriguez: And how long do those take?

Meghan Barrett: That’s a good question, and I don’t have good answers for you on that, because it’s so standard operating procedure-dependent. It depends on the amount of material or the number of insects that you’re putting in. It depends on the shape of the machine: imagine a microwave that’s shaped like a circle, and then you put in a bunch of layers of larvae and it spins them around with a little disc and is constantly mixing them, versus a conveyor belt style that they’re going through: the more layers of larvae there are, the longer it’s going to take for those larvae, unless the power of the machine adjusts for that by being a more powerful machine.

It can take minutes, that’s for sure. In the microwaving case, it can take minutes. And that method, really the way that microwaves work, of course, is those water molecules moving faster, so it’s sort of like boiling from the inside. Not ideal, potentially.

Luisa Rodriguez: That sounds really horrible.

Meghan Barrett: I’ve conducted some work independently, my lab and Jeff Tomberlin’s lab at Texas A&M University . We’ve conducted a study that just got accepted at Animal Welfare . You can find all the materials for this study as a preprint , with a bunch of supplemental videos and things like that too.

So that study is looking at humane grinding SOPs [standard operating procedures] for black soldier fly larvae, where we basically try to determine what machine design constraints and larval body size constraints may matter for producing an instantaneous death using basically a meat grinder. And it turns out that under certain conditions, you can actually get to like a 99.4% likelihood of instantaneous death, which is pretty high. And if you do it wrong, you can get like a 58% chance of humane death. So it’s important to consider the constraints of your machine, because you can get a lot of variation otherwise.

I think more work on that is clearly necessary, because grinding is actually not probably a method that many producers will want to employ at scale. It oxidises the lipids inside the animal very quickly, because you’re basically spilling their guts to the environment, and that has some effects on product storage and quality. So it’s not probably a preferred method, although it could be good in depopulation situations where, say, you have a big outbreak of disease, and you don’t want to use your regular slaughter machinery, because then it would get all gunked up with potentially disease-causing microorganisms, so you might want some alternate method. This could potentially be explored, and I hope to explore it further as a humane depopulation strategy for the industry.

Luisa Rodriguez: How about disease? Do farmed insects suffer from insect diseases?

Meghan Barrett: This varies a little bit across species. In crickets, disease has already been a huge problem. One of the most popular crickets to rear, the house cricket, there’s the densovirus that has actually been such a big problem that it has caused the industry to switch to two other species, because it’s caused whole colonies to collapse in both Europe and America. Not everybody has switched, but many facilities have switched to two other species of crickets that are much more resistant to this densovirus. But crickets get a lot of viruses. And I think we don’t even have a good sense, from some research talks I saw at this year’s Entomological Society of America conference, of how many diseases are out there. There’s way more than we realised across facilities for crickets.

Mealworms can be susceptible to some diseases, but appear to be much less so than crickets, from the reading that I’ve done and the reports that I’ve read. And black soldier flies have been touted as kind of the disease-free insect of the insects within food and feed space. And there’s some reason for this that biologically is accurate, which is that they are filth-feeding flies by nature, so they’ve evolved in these very microbially rich environments, like filth typically is. And so they have all these antimicrobial peptides that are helpful for them in managing the likelihood of getting a disease from their environment. So there’s good reason to suspect that they will be more resistant to disease.

The problem, of course, is that anytime you start to rear an organism en masse, you almost inevitably end up with diseases developing that can take advantage of that circumstance. And particularly if you start to see inbreeding depression , like reductions in genetic diversity in your population — which are also sometimes common in farming situations where people are not constantly reintroducing genetic diversity.

So we have started to see reports, the very first reports trickling in, of major disease outbreaks for black soldier flies in the actual scientific literature. The first one was from this past year, called soft rot. It kind of rots the body of the insect. I believe it’s bacterial. And that’s the first one in the literature of an epidemic.

But if you go to YouTube and look at what producers are posting videos of, there have actually been older reports of producers, of their colonies collapsing as a result of unknown diseases. And part of this is that we know so little about insect diseases: just fundamental basic knowledge, we know so little about them. So that makes it hard for producers, when they’re seeing particular collapse problems, to even know what might be causing it. Is it abiotic? Is it a disease? It can be very challenging to assess what’s going on in these cases.

Luisa Rodriguez: And just to give a bit of colour, obviously diseases are often bad, some are worse than others. Do we have some sense of what the more common diseases in these particular species are like to experience? I guess you’ve already mentioned one causes your body to rot, which potentially sounds horribly, horribly painful. What else do we know about them?

Meghan Barrett: That’s a great question. It’s very complicated because I don’t think we have a good sense of what the insects’ experience is in any of these cases, to be perfectly honest. I mean, we see a range of possible changes both to behaviour and physiology. For example, lethargy is often quite common, or even paralysis happens, in what’s called cricket paralysis virus. So then they typically end up starving to death sometime after they end up paralysed. There’s things like that; there’s diseases that cause sepsis. And so insofar as we are willing to extrapolate from other animal cases, we would assume that these are unpleasant, many of these.

I do also want to note though that we have really acute infections — and those tend to be what we notice, because they cause big epidemics and kill lots of organisms and are really severe. So those we might expect to be quite bad, but there are often many kind of underlying latent infections, where a disease persists in the population, but doesn’t seem to cause a tonne of negative fitness or decreases in survival, changes in behaviour. So I think it can be something like those diseases might not typically be so bad, but then when some additional stressor happens — the temperature gets too high or nutrition isn’t quite right — then the animals suddenly experience an acute infection and things get really bad.

So I think there’s a lot to tease apart there on the latent versus acute difference, where sometimes the same disease in a different population phase could matter differently to the animals’ experience.

Luisa Rodriguez: Yeah, that all makes sense.

Inadequate nutrition, density, and photophobia [02:53:50]

Luisa Rodriguez: So that’s inhumane slaughter practices and also disease. What other kinds of things might these insects experience?

Meghan Barrett: Then we start to get maybe interested in some of the more species-specific cases. So what’s different for black soldier flies versus crickets? Or something like that. There’s going to be a lot of cases where we’re talking about inadequate nutrition or inappropriate abiotic environments or inappropriate densities, things like that.

A great example of one of these phenomena would be for adult black soldier flies. There’s this misconception that adult black soldier flies can’t consume food. And this is actually not the craziest-sounding thing. I see your face, but this is not the craziest-sounding thing, because in other farmed insects this is a thing. So adult silkworm moths actually don’t have functional mouthparts and don’t consume food in the adult life stage. And there are species of insects that have this strategy, where they consume mostly nutrition as a larva, and then when they turn into an adult, they actually don’t consume food and they’re focused entirely on reproduction — so growth happens in the developmental period and then reproduction happens as adults.

So it’s not insane for people to think this. I just want to be really clear on that. The problem is that it’s not true. Adult black soldier flies can consume food: they have functional mouthparts, they have a functional digestive system. If you feed them, it increases their longevity. They gravitate towards and consume certain food substrates that are provided to them. They actually even have — from data that my lab is collecting with Ed Waddell — preferences for certain kinds of nutrients over other kinds of nutrients. So totally capable of eating.

So this is at the adult life stage. Where this misconception came from, I should say, is that the adults will lay eggs before you have to feed them. So if you don’t feed them, they will still lay eggs and your colony will still continue. And so this kind of turned into a “they don’t eat” phenomenon.

I think the first studies on this were like 2016 or so. People started feeding them carbohydrates, like straight sugar, and were like, “They seem to be eating this sugar. It’s kind of weird. And then they lived a lot longer. What’s that about?”

Meghan Barrett: So it’s a very new field to be thinking about adult black soldier fly nutrition. But what this means is that on farms, they are not typically provided with food, sometimes not provided with water, and this predictably causes them to die over a period of about eight to 12 days. So that’s one species-specific practice.

Yellow mealworm adults, for example, will not lay eggs if you don’t feed them and provide them with an oviposition substrate, which is an egg-laying substrate. Oviposition is egg laying. So people feed and provide oviposition substrates to adult yellow mealworms.

So that’s one example of potentially a species-specific concern for welfare that could potentially be addressed with the right kinds of research, once we figure out what’s good for these animals to consume, what they prefer to consume, if it changes over the course of their lifespan, those kinds of things.

Another example could be density in crickets. Crickets can be found in high-density situations in nature. Think about their cousins, the locusts: everybody’s familiar with that example. So crickets, too, often are found in high densities in nature, but many of them have dispersal strategies that are based on density. For example, they might have small wings if they’re in a low-density environment, but they might develop big wings if they’re in high-density environments — and those big wings let them fly further away so that they can get out of that really bad density environment.

Luisa Rodriguez: That’s very cool.

Meghan Barrett: Yeah, isn’t that cool? “Wing polymorphism” is what it’s called, where you can have more than one morph in the same species. So not all crickets do this, but some of the farmed species do. Not all of them. You might imagine that we’re rearing these crickets at pretty high densities. They may sometimes be developing these large wings that are indicative of a behavioural dispersal activity that they tend to perform if they were in nature. They are not going to be dispersing on farms; dispersal is not an option. So we are constraining them potentially at densities higher than what they would prefer.

And there are some reports from producers that when you rear them at too-high densities, you get cannibalism and increased aggression, because this is another way to lower density, is to eat the other insects in your environment, so then the density is lower. So when densities are too high, it can lead to potentially suboptimal density-control mechanisms, like cannibalism. Now again — because all I like to do is talk about uncertainty all the time — we should mention that cannibalism causes mechanical injury, and we have some reasons to be sceptical about mechanical injury and whether or not that’s truly a source of pain in insects. But certainly it’s an avenue worth further investigation.

And we think of one of the important components of welfare being the ability to express natural behaviours. So in this particular case, dispersal away from a high-density environment might be considered a natural behaviour for these wing-polymorphic species when they’re in the large-wing morph, and they’re not being provided with that opportunity to engage in that natural behaviour. That might also be, independent of the concern of cannibalism, concerning to us from a welfare perspective.

Luisa Rodriguez: Yeah, sounds totally plausible. What other categories should we be worrying about?

Meghan Barrett: Another possible category of concern would be thinking about the fact that all these species, at least at some life stages, are photophobic. Adult black soldier flies are the exception here: they actually like plenty of light in their environment; it’s important for mating. But everybody else — larval black soldier flies, and adults and nymphs or larvae of the other [mealworm and cricket] species — are going to be photophobic. And this means basically light afraid, if you will, photophobic.

This doesn’t mean that you shouldn’t ever have light as part of setting their circadian rhythm, but it means that light can be really stressful for these animals when they experience it directly. You can imagine that there are many times where these animals might be subjected to light stress as a result of their handling and rearing.

For example, as part of routine activities, you’re sifting through the substrate that the mealworms are in to turn it over and check that they’re all healthy, and you’re subjecting them to light while you do that. For crickets, one of the harvesting mechanisms is actually to kind of dump them all into a bin that has a little escape hatch from it into the collection bucket, and then you shine a bright light on the other bucket so they all run into the collection bucket. And that separates the dead ones from the live ones, and the live ones from any other materials — like frass, which is insect poop, and stuff like that that might have otherwise been collected and made it into the final product. So that’s one way of trying to use their natural desire to escape light conditions, to move away from that and go into this collection environment; one of several ways of potentially controlling the movement of that species.

So I think that’s another area of concern. And I should be clear that not all these concerns are present on every farm or facility — like we discussed, there’s a lot of variation. Some of them, I think, are really common. Like the inhumane slaughter problem is one that’s probably, just because we know so little about how to do it well, shared across many facilities.

But I think other things might be… I know of producers, for example, who use red lights when they’re handling their insects. So insects cannot see — most insects, probably all, but I’m going to say “most” because of the diversity problem, maybe I don’t know one — most insects don’t seem to be able to see red. Certainly all the farmed species cannot see red light. It’s sort of like if you’d shone a near IR light on me, I wouldn’t be able to see it. So if you use red lights, the humans can still work safely in the environment by being able to see, but the insects can’t see it. That’s one way to improve conditions for photophobic species during handling. I know some facilities that are already doing things like that to try and improve conditions for the animals.

Most humane ways to kill insects at home [03:01:33]

Luisa Rodriguez: And just as a side note for people curious, how should I, if necessary, humanely kill an insect in my home?

Meghan Barrett: Oh, great question. It sort of depends, like everything that I say on this topic. The first thing is, if it’s a really, really, really small insect, probably honestly, the best thing you can do is squish it really fast. Like really fast: just whole nervous system done. I know that doesn’t feel good, but honestly, it’s probably the safest with the knowledge we have right now on how to do it.

Then we start to get into debate territory. Many entomologists would recommend to you that you put the insect in a freezer and let it cool down until it dies. I have some concerns about this, where I would want to see further research to address them. The first is that the idea here is that because insects are ectotherms, you’re just sort of slowing their metabolic rate until they lose consciousness, and then they die of being cold after that. This is true.

And yet veterinarians do not recommend that we freeze other ectotherms to death, like fish or lizards. It’s not appropriate. And one of the reasons for that is that the periphery cools at a different rate than the kind of internal system cools. Now, insects are often — although not always, as we’ve discussed — much smaller-bodied. So you might imagine that the periphery and the central part of the nervous system cool at a much more similar rate.

But also, we don’t actually know a lot about how insects experience cold. I mentioned earlier that we know that heat seems to be a problem for them. We know much less about cold. One big issue there is that most of the behavioural studies that we do looking at how insects respond to heat stress and cold stress rely on behavioural indicators. And insects’ muscles can move when they’re too hot; they can still move their muscles until they hit that lethal point. As they cool, there’s a locomotor confound where their muscles stop working, potentially before their nervous system stops sending signals to try and get the muscles to work. It’s sort of like when you’re too cold and your fingers stop really being able to move, even though your brain is still trying to get your fingers to move. We don’t know when that’s happening for insects, because they can’t tell us when they’re not moving because their nervous system has shut down, or when they’re not moving because they can’t get their extremities to move.

And we do have some evidence that concerns me that cold could be painful. Some of it is from unique nocifensive behaviours evoked in fruit fly larvae in response to cold . Some of it is reports from producers on crickets trying to escape when they put them in the freezer — they all try to escape from it. I think this idea that cooling too rapidly seems like something that would be bad for insects, and so there’s sort of an adaptive value for them to avoid cooling too rapidly. Whereas potentially cooling very slowly, like you imagine insects might go through each day, a warmer period and a cold period, day and night.

So we shouldn’t necessarily expect all cooling regimes to be painful to them, because imagine — like we talked about with the naked mole-rats — if your environment was constantly painful to you and there was nothing you could do about it, it’s not helpful information for you adaptively. So if insects are constantly warmer and then cooler, warmer and then cooler, then slow warm/cool cycles might actually give them enough time to physiologically adjust to the temperature change for it not to be painful or perceived as painful. But I think we need more research on that: what rates of temperature change are better or worse?

There’s just a lot of open questions for me on the freezing side of things, where I’m a little sceptical of the entomological community recommendation of just pop them in the freezer and it’s all OK. I can’t tell you that it’s bad, because I don’t know that it is. I’m just saying I’m questioning.

Luisa Rodriguez: OK, so that’s our nice digression about that.

Meghan Barrett: I’m sorry. It’s a very commonly repeated refrain and so I have lots of thoughts about it. The last thing I’ll say is boiling and blanching, if you’re doing a single insect at a time, and they are smaller-bodied species — so not like really big cockroaches, I would not recommend this for — but I have tested myself the body temperature of a black soldier fly larvae. If you drop them one at a time into boiling water for one second and pull them out, they are well above their critical thermal maxima — are dead, is what that means — one second after being dropped in boiling water. So if you, for some reason, are unwilling to squish the bug, I guess that’s what I’d recommend next. But squishing is probably your best bet.

Luisa Rodriguez: OK. Yeah, I don’t plan to squish any bugs anytime soon, but I do feel like for most of us, it’s the most common interaction we may have with an insect in our actual life. And some people might wonder.

Meghan Barrett: Sure.

Luisa Rodriguez: Have we covered a lot of the things that worry you most? Is there anything that you haven’t mentioned that seems pretty bad if insects feel pain?

Meghan Barrett: I think the only other thing that makes me really concerned is something that’s not really happening yet at scale, but is something that might happen in the future and makes me a little bit nervous. That’s the genetic modification of these animals and selective breeding efforts — which we know from vertebrate research that selective breeding programmes, for example for chickens, have caused a lot of the welfare issues that chickens are currently experiencing on farms . So we might be similarly concerned for some of the selective breeding or genetic modification programmes happening with insects.

Those are really early-day programmes. Some of the first GMO lines are just starting to be advertised this year, basically, and their welfare impacts are unknown. It’s entirely possible that some of these genetic modifications could potentially even be welfare positive. But I think if we don’t actually do the research concomitant with the genetic modifications in selective breeding, we run the risk of repeating previous agricultural mistakes.

So I’m hopeful that people who are doing these selective breeding efforts or these genetic modifications will consider adding welfare studies to the work that they’re doing on productivity and things like that, to make sure we’re considering the full picture of what these genetic modifications do before we actually implement them at scale.

Luisa Rodriguez: Nice. Cool.

Challenges in researching this [03:07:53]

Luisa Rodriguez: To what extent do we already have, I don’t know, like an insect welfare research toolkit for the farm context? I’m asking because lots of the things you’ve mentioned that sound bad for farmed insects, and lots of the things you’ve mentioned insects seeming to prefer and not prefer, like light and heat in particular, maybe over things like mechanical bodily harm, makes me realise that we actually probably don’t have a great sense of what the farming practices are that are really harmful, and what the kind of best reforms are to improve those practices.

Meghan Barrett: Yeah, definitely. There are a lot of challenges here. On the one hand, for many of these species, we have a pretty decent understanding of many of the facts of their basic biology. That’s especially true for mealworms and crickets that have been study systems for a while for many behavioural questions, or in the mealworm case, for immunity questions and disease questions. The black soldier fly we actually know a lot less about their basic biology. It’s kind of a challenge.

So a lot of our information right now for these kind of foundational welfare papers of where we should explore and what we already know are based on the basic biology of the species, studies that have shown us they’re photophobic and things like that, as well as kind of survival-level information. If they’re not surviving, they’re probably not thriving at a population level, so we can imagine that low survival rates are indicative of pretty serious welfare harms.

Of course, we know nothing then about the sublethal welfare issues in these species from a really solid perspective, because we don’t have nearly as much data either on those issues at all, or we don’t know how important they are to the experience of the animal. Even if we think they might have some welfare consequence, we don’t know the amount of welfare consequence they might have.

So there is a lot of challenge here to sort of developing the field of insect welfare research. On the one hand, we can rely on some tools and techniques from welfare science writ large. They are still animals, and so we can study them the way we study animal welfare. On the other hand, there are things we need to be really careful about in terms of building this new field and not taking too much from vertebrates that shouldn’t necessarily be applied. So we shouldn’t assume that insects are going to respond the way vertebrates respond to all different welfare challenges — like we’ve discussed at length in terms of mechanical injuries, for example. There’s a lot still to research there.

There’s also other challenges on the frontier for this growing field. One is the fact that this is such a novel industry and it’s growing so rapidly, and so we haven’t even seen the largest facilities: what they’re going to look like, how they’re run, we don’t know anything about if there’s going to be selective breeding or genetic modification and what that will look like. And keeping pace with that industry development — when you are a handful, to be honest, of interested welfare scientists — is really challenging.

That rapid innovation, the fact that new species are also constantly being explored for potentially mass-scale rearing. And if a new species comes about, I mean, that’s a whole other field. It’s like, if you added minks, you’re not going to say, well, probably what we have learned about turkeys is fine for minks, right? No. Now you have to do all of mink welfare all over again. So like palm weevils: now we’ve got to do palm weevils; silkworms: now we’ve got to do silkworms.

So I think that industry growth and innovation is a constant challenge to keep up with — both the tools and the species. There’s that vertebrate/invertebrate distinction I talked about. There’s the developmental problem, where you’ve got these different welfare needs across these very different phases of development. Where the juvenile needs — especially in the holometabolous insects, those ones with the complete metamorphosis — are very different than the things that the adults might need. So it’s almost like dealing with two different species at the same time.

Luisa Rodriguez: Sounds like it.

Meghan Barrett: Even though it’s one species. They live in different environments, they have different nutritional needs, they have different abiotic condition needs, their physiology is different, their behaviours are different, their morphology is different. The larvae and the adults are basically, for all intents and purposes, two species in this particular case, just linked by pupation — where again, things from the larval stage could potentially affect the welfare of adults later on. So there’s that.

I think also one challenge that we face is kind of a bigger level, outside of the science, but more societally, is the interspecific tradeoff question. So my understanding from the literature that I’ve read is that black soldier fly larvae can be a good enrichment for chickens, that it could potentially even improve their immune function because they get some benefits from the antimicrobial peptides that are found in the black soldier fly larval bodies. Also, for fish, there can be some benefits to their development. In certain species, their ability to hear is impacted by consuming more insect protein versus other kinds of protein [according to unpublished data (personal communication)].

So now we’re saying, we’ve got chickens, we’ve got fish, and we’ve got black soldier fly larvae: how do we feel about that interspecific welfare tradeoff between those different species? I think that’s going to be really complex to untangle, because we need to know more about the degree of welfare harms, of anything we think is a welfare harm for these animals, and the degree of benefit of the welfare positives we see for the fish and the chickens in this case, before we can really make that determination. And we’re so far from that, even in some of the vertebrate species, especially fish, that it makes it really challenging to know how to proceed in that case.

Luisa Rodriguez: Yep, I hate that research question. I nominate someone else to take that on.

Meghan Barrett: Correct.

Luisa Rodriguez: Were there other challenges?

Meghan Barrett: Let’s see. I think the scale question, if we go back to thinking about that, it also produces a challenge. So you’re rearing many, many, many more animals and you’re going to get, because they’re insects of this particular set of species, their generation time is relatively rapid. Very rapid in the case of the black soldier fly, slightly less so in the case of the mealworm — but still rapid enough compared to a chicken or a cat.

So rapid generation times in these relatively isolated facilities leads to significant population divergence. Like, if you and I were both insect farmers: you had a facility, I had a facility; our facilities aren’t exchanging genetic material between our populations, potentially. We’re both rearing our own insects and we’re rearing them under different conditions. Like, maybe you provide them with water more often than I do. What that means is we have created little ecosystems where we are exerting selective pressures, based on our farming choices, onto our populations, and they will begin to diverge.

Luisa Rodriguez: Right. That’s wild.

Meghan Barrett: Yeah, exactly. This is a problem we have in lab environments when we rear insects, where everybody’s using Drosophila , but their lines have diverged so much from each other over being reared in the lab for 50 years on this super short generation cycle, that you start to see differences in the populations depending on how they’re reared. And we try to accommodate that in labs by rearing them as similarly as we can. But of course, producers are trying to innovate, they’re trying to find ways to be different from the competition and improve their practices compared to the competition. And that may lead to this divergence over time in the industry as conditions are different.

So now, let’s say you’re an independent welfare scientist and you’re like, let me provide the industry with a recommendation for the temperature for rearing mealworms, and I provide that recommendation to you and to me. It’s possible that’s a great recommendation for my facility — my mealworms might do phenomenally — but maybe you were rearing your mealworms at a temperature 10 degrees lower than me for the last 20 years, and so your mealworms don’t do great when you raise the temperature 10 degrees. I’ve now given you a bad welfare recommendation because I didn’t take into account the differences between the study populations and the resultant producer populations. So there’s variability.

Luisa Rodriguez: Yeah, that feels super surprising to me and isn’t something I’d considered at all. But I’m curious, does the amount of differentiation that can happen over these timescales make that big of a difference? Is it possible that you could end up with populations that prefer such different temperatures that one could have much worse welfare than another?

Meghan Barrett: This is a good question. I’m not sure on the temperature case, how strongly I would say for that variable. I think for more multifaceted situations, it gets more reasonable to assume that the genetic differentiation question matters a lot.

For example, nutrition could matter a lot, nutrition and hydration, things like that. There’s one study that was conducted in mealworms , where they collected strains from a bunch of different production facilities and demonstrated that they grow and survive very differently under the same nutritional and hydration regime. Because of these differences, you might get 10% or 20% differences in survival — which, when you’re talking about this number of animals, is a lot of difference in survival.

So I do think there’s cause to be concerned that, yes, this variation, for some variables, is going to matter more than for others. I’m not sure where I put my certainty on the temperature piece of it, but I do think the evidence so far bears out that density, nutrition, and hydration can all be significant in this way.

Luisa Rodriguez: Yes, that makes sense. And those sound like incredibly difficult challenges. It does sound like you’re almost on hard mode. You’ve got orders of magnitude more species, and then each species has different subspecies, in effect, because of this ageing thing. Different populations also create different species, almost. So you have your work cut out for you.

Meghan Barrett: And just to really complicate it, also imagine that within a population changes over time, right? Where maybe I study the population in 2002, but that recommendation, because of this internal selective environment, is no longer good by 2022. There’s been examples of rearing crickets where they actually increased their aggression in response to being reared at high density, so the density recommendations you can make to get aggression to a manageable level in crickets of the latter population versus the earlier generations of that same population would be different.

I think that’s probably an issue that is not just seen in insects — you’re going to see that in chickens over time, and cows over time — but you’re going to see it much more rapidly happening in insects because of the rapid generation times of these species. So your divergence just happens a lot faster.

Most promising reforms [03:18:44]

Luisa Rodriguez: That sounds really hard. Thinking about potential solutions, is there a single potential reform that you would be most excited to see implemented in one of these sectors?

Meghan Barrett: I think for me, the most exciting and feasible — because I’m excited about feasible things — so when I think about feasibility, the main questions of interest to me are about stunning in slaughter and depopulation.

So with depopulation, I think one of the easiest things that we could potentially recommend to producers is things like, this is a waste population, if you will — because you’re not going to be selling them as product. Let’s find a way to kill this population quickly and reduce their suffering.

And if it’s inexpensive and not labour intensive, it should not be a hard ask of the industry, in my view so far. Obviously, I need to talk to more industry people about that, but I think it’s one of the more feasible requests that could potentially dramatically improve welfare for a population of animals we believe is suffering from some kind of disease or other inadequate condition, which is why they need to be disposed of.

So in that case, although we still want a little bit more data on grinding as a method of depopulation, I feel reasonably confident that we could recommend, especially for black soldier flies, some standard operating procedures for grinding for depopulation that would probably improve things for those animals being depopulated. So that’s one area I think is important and potentially feasible.

I think the next area is not as feasible yet, but is likely to become feasible most rapidly, and that’s stunning in slaughter. We don’t know what we’re doing yet, so I don’t recommend anything precisely at this moment in time — other than maybe really don’t rely on those super inhumane methods, like microwaving: maybe we should be moving away from those. But I don’t have a solid recommendation for what we’re moving towards yet, which I understand is a problem.

But I think the research will come out soonish on those topics; more than on other topics, the research will come out on those, and then they should be probably implemented by producers in a species-specific, standard operating procedure kind of way to improve that. Because I think also consumer interests are going to drive interests in humane deaths for these animals. So it’s advantageous both for the animals and for the industry to take that issue seriously once the empirical data is there to support better practice.

Meghan Barrett: The last one is a little self-serving, because I’m just really interested in it. And that’s black soldier fly adult nutrition. Again, I think once we know what combinations of carbohydrates and proteins we can provide, and once there’s been some research on how that impacts productivity — because I actually think there could be some productivity benefits based on feeding the black soldier fly adults, and some genetic benefits to colony health as well — if those bear out, I think it might not be too expensive to actually do this change where you’re just putting a feeder in and changing it like once a week or something like that to make sure it doesn’t get too dirty. The materials are like molasses and yeast, so these are not super expensive things to have to buy in the amounts needed to feed a population of adults.

So that’s something I’m excited about too, that I think could potentially, once we figure out how to integrate that with producer processes and figure out how to do humane culling of adults — because now the problem is that they’re going to live much longer, past their age of optimal reproductive viability. That’s another area where I’m excited to partner with producers, and have been talking with producers about how we can maintain the efficiency of their processes, but be more humane for the animals as well.

Why Meghan is hopeful about working with the industry [03:22:17]

Luisa Rodriguez: OK, nice. I guess it seems like we might be at this pivotal-ish point in the rise of this industry, such that it’s at least plausible — and correct me if I’m wrong — that welfare practices might be more malleable, because we haven’t gotten these massive farms. And so before we have those, it would be good if we had more confidence in our guidelines about which practices they should try to adopt, and they haven’t already invested in all of the machinery, such that it would be really hard for them to change all of their practices if you came out and realised that some practice was particularly bad.

Are you hopeful that these kinds of reforms could be put in place before the industry gets potentially many orders of magnitude bigger, and kind of established and inflexible?

Meghan Barrett: I am hopeful that at least some of these reforms could get implemented. I think the reason I’m hopeful is multifaceted — so there’s also that to keep in mind. But the first thing I consider is how many producers have reached out to me on the basis of my publications to talk about some of the recommendations that we make, and whether it would work or not in their facility, and what they might do better.

I do think that especially many of the insect producers that initially got into this industry were driven by the ethics of it from an environmental sustainability perspective. They want to provide protein to feed the world in an ethical, sustainable way. I’m not going to say everybody is motivated by that, but I think many of them are deeply thoughtful people who care about the ethics of what they do and want to leave a positive impact on their world. And this is the way they see to do that.

I’ve been really impressed, actually, by how many producers have reached out to talk to me independently; have invited me to come speak to their staff or their R&D team; who have opened up about what they’re doing and what they’re struggling with, so that I could potentially try to provide recommendations that they could help to solve some of their specific challenges in their facilities.

There’s been a surprising amount of interest from producers, and a lot of discussion. So the International Platform of Insects as Food and Feed, before anybody was asking them to, they created this little welfare guidance document . It’s very short, and it mostly admits a lot of what I’m saying here, which is that we don’t know a lot of things we need to know. But nobody was asking IPIFF to produce that document, as far as I’m aware, and they generated it proactively anyway, to say we need more research on this topic.

AFFIA , which is the Asian food producers group, recently invited me to give a member event talk on the welfare of insects as food and feed. At Insects to Feed the World , which is the major international conference for the industry, they invited me to give a keynote on insect welfare at this year’s conference.

Also, in my work with the NSF Center for Environmental Sustainability through Insect Farming , our industry advisory board actually led the charge for creating an animal welfare committee this year that I now chair, and we have a lot of exciting work planned there too.

So I think it’s a topic that a lot of people, especially the trade organisations, are taking seriously, want to know more about, and are interested in having productive dialogues on what’s feasible, what we know, what we don’t know, how they might help us figure out what we [need to] know.

Yeah, I have some hope for that. I do think it’s inevitable that the science is going to progress slower than we would want it to, because that is how science tends to work. So we’re going to miss some key moments where we will provide recommendations after the industry has settled on some kind of potentially low-welfare standard practice. That seems inevitable to me. And then we’ll be asking people to make potentially expensive changes, and that will probably be a more challenging conversation. But I think right now, because there’s flexibility in facilities being built, the industry is so innovative and new, and many folks are interested in this conversation, there’s been a lot of positive discussion on what we could do better at this time.

Luisa Rodriguez: Yeah, that actually is a great segue to the motivation behind the rise of the industry, which we haven’t really talked about yet. My sense is that it’s in many cases very humanitarian and environmental in its origin. I feel like maybe it was the FAO that put out this report saying that insect farming could be really phenomenal for the environment and for global food security. And I think it was the UN that promoted it as a way to feed something like 10 billion people by 2050.

Meghan Barrett: Yes, that’s right.

Luisa Rodriguez: OK, nice. So can you explain exactly the case that these producers are making for insect farming? It really seems like they’re promoting it as a massive solution to a bunch of different world problems.

Meghan Barrett: I can do my best. I would say I am not a sustainable agriculture scientist. I am somebody who focuses on organisms and their biology. I know some of the general facts, but it’s really just kind of knowing the general facts and I can’t do a super in-depth job, but I will do my best with the general facts I know.

So basically we have all this super unsustainable vertebrate agriculture that I’m guessing people are pretty aware of. It’s because of the [greenhouse] gas production from those animals, and the land usage of those animals, and the water usage, and feeding them plants which we then also have to grow to feed to them for them to be fed to us, et cetera. So we all are pretty aware that animal agriculture is not very sustainable the way that we are currently practicing it.

And also, it can lead to challenges with food security, because not everybody has adequate access to the kinds of resources needed to produce protein in the requisite amounts. This is especially true for folks in low- and middle-income countries, where they may have fewer resources available to them to generate the kinds of protein they need to sustain their populations.

OK, how can we try to solve this problem? Because we certainly don’t seem to be having fewer people. So what do we do? Well, the first thing we could do is we could look at these waste streams that we have. So typically this is stuff that just kind of goes to rot. We waste a tonne of food in the United States, like a tremendous amount of food from our grocery stores, directly from farms.

So what if we could take that waste and we could turn it back into usable protein? Now we’re not having to grow additional usable protein, and we’re getting rid of this waste substance. That’s one of the promises of the industry, especially for species like the black soldier fly. There are other potential substrates that can be reclaimed by the yellow mealworm, for example, it appears like they may be able to reclaim what we call mycotoxin-contaminated grains. Mycotoxins are these toxins produced by fungi, and they’re very dangerous to vertebrates. So if we have grains that are contaminated that way, we typically tend to waste them. But it appears like insects may be able to eat them and then again turn their bodies into protein that we can feed to vertebrate livestock without it being dangerous for the vertebrate livestock to consume them.

There’s the fact that we are overfishing, so if we could replace some of fishmeal with insect protein, that might also be beneficial for some environmental reasons, just from a biodiversity and conservation perspective.

And then when we get to the feeding people in low- and middle-income countries perspective, a lot of these insects can be reared with, again, waste streams — like genuine waste that people are producing in their local area. And they can be reared inexpensively and at scale and often year round, depending on where you live and what species you’re talking about.

That’s why, in many countries, actually, insect farming has a long history, like in rural Thailand, for example. This is a protein source that is accessible to these folks all year long in many cases, and without needing to worry about expensive rearing equipment and machinery, or even expensive animals themselves, because it can be expensive to buy a cow in some of these countries. And then you have to wait a long time for that cow to get big enough to eat it. And then you got to do something with all that meat that you get one time, one time when you slaughter. You don’t have that same problem with insects. It’s a more continuous source, relying on the waste that you yourself are producing.

So those are some of the promises, I think. Where it goes potentially wrong, and where we probably need more sustainability analysis, is if we aren’t feeding them waste substrates — so we’re feeding them things we could feed directly to humans or vertebrates. Now we’re just introducing more middlemen into the food chain, and so maybe it’s not as sustainable in those cases.

Luisa Rodriguez: Yeah. And the issue there is, every time you add a so-called middleman to the food chain, it becomes very inefficient — because, I don’t know, a chicken has to grow feathers, but people don’t eat the feathers — and so maybe you lose some of these environmental benefits, I guess is the idea here?

Meghan Barrett: Exactly. Yeah. Because of the increased inefficiency. Exactly. So that’s one potential challenge: if we’re not eating them ourselves, if we’re not feeding them on waste substrates and are instead feeding them on things that could be fed to humans or other vertebrates.

Luisa Rodriguez: Is this a big issue? Because not very many people I know are that excited to eat insects, or to even have them even as ingredient components in other things they eat. And I know that my experience is an experience of a person growing up in the US and living in the UK, and that is not the same everywhere in the world.

Luisa Rodriguez: Some people are very happy to eat insects, but it’s a pretty big part of the world that I think is not thrilled about the idea. And so it seems like a huge limit to those potential benefits if a majority or even just a large proportion of these insects are fed to middlemen like chickens and cows.

Meghan Barrett: Yeah. And again, that’s based on if those waste streams can or can’t be reclaimed other ways and also if we’re feeding them based on a waste stream too, right? So like, waste stream versus product that is accessible to vertebrate consumption will change the calculations there a bit. But you’re right. Basically, you’re right.

And as far as the dietary preferences thing, I am not a sociologist or whoever you would need to be as an expert on human behaviour. I do think it’s interesting that in other invertebrates, we’ve seen significant shifts in dietary preferences. So for example, lobster for a long time was like, “I would never eat that rat of the sea!” And then people were like, “Lobster: fine dining.” So we know that dietary preferences shift. Whether or not that will happen in the insect case remains to be seen. Right now, they’re certainly a novelty item for human consumption in the West.

Meghan Barrett: Not so much in other countries, but in the West.

Luisa Rodriguez: Makes sense. It sounds like this industry does have some promise, but also there are going to be a bunch of complicating factors that could totally flip the sign. Like in practice, do life-cycle assessments show that the industry is actually more sustainable than other things we could choose to be doing, or do all the specifics end up flipping that? And also, as we’ve been talking about at length, does this just look like a really terrible idea on insect welfare grounds alone? It seems totally possible to me at this point.

So I guess it sounds like the jury is still out, but it sounds like there are at least a few more reasons to be sceptical that it’s going to deliver all of the benefits that the proponents have been suggesting it will?

Meghan Barrett: Sure. I mean, I think these proponents are talking about specific cases. So when we’re thinking about the life-cycle assessments and what they show, there are many LCAs that do show — in specific cases, under specific SOPs and constraints — these environmental benefits. So I want to be clear that there are cases where that’s been proven to be true in the literature .

So yeah, I do think there are many potential benefits. Of course, like all industries, those benefits depend on how we actually do the thing. And so we need to be careful and considerate in how we do the thing.

Careers [03:34:08]

Luisa Rodriguez: OK, that is where we’ll leave insect farming. Let’s talk a bit about how people can use their careers to work on this problem. If someone is inspired to work on insect welfare, what kinds of work needs to be done? What’s the need?

Meghan Barrett: Oh, we need so much. So much. If you are somebody who wants to use your career to work on insect welfare , for sure we can find a way to use your skill set and expertise, because it seems like every area we could use folks right now.

So obviously, there’s folks with backgrounds like mine — research folks, folks with experience with insects — where we could just use fundamental research on these species and what could improve their welfare, even just like basic research on their behaviours could actually be very valuable. Because like I mentioned, for the black soldier fly, we know almost nothing about its natural behaviours, which makes it really hard to know when we’re providing opportunities for natural behaviours in farms or not, which is an important component of welfare. So there’s that piece of it, the research piece.

I do think the questions about can we incorporate welfare into our LCAs to kind of get at what you were saying about, is this good or bad even just from a welfare perspective? I would argue you should incorporate the sustainability and the welfare benefits together somehow. So can we incorporate sustainability and welfare into an LCA and then see how it comes out? That might be a better way of doing it than just considering each part piecemeal. Some economists could be really helpful for that.

Obviously, we could use people on the insect sentience side of things, who are neurobiologists, consciousness researchers, pain researchers, et cetera, that don’t even necessarily have a background in insects, but could start working in that model because they have such valuable information stores and skills available to them.

Let’s think about people who generate various kinds of content for a living. All of those people could also be really valuable, because, as we have discussed a lot, there are so many incorrect assumptions about insects and intuitions about insects that need to be overcome. And this could actually help not just from the welfare perspective, but also from a conservation of insects perspective — because there has been a lot of discussion about biodiversity loss in this group, and there’s reasons to be concerned about that, independent of the welfare concerns for our world.

So you might imagine, if you’re somebody who works on generating content for the public, this is a great way to educate the public to be more aware of these kinds of concerns that have to do with this group of animals that are very poorly understood. And again, from both welfare and other potential aspects, just dealing with the fundamental lack of awareness about insects is valuable, in my view — as an entomologist who loves insects.

If you are a producer, being able to lead conversations in your community — whether that’s your facility, your R&D team, your trade organisation — saying, “Hey, this is probably something we should start taking seriously. Let’s have a conversation about how we could do that and what’s feasible for our industry or our organisation at this time.” That’s also a great place to start, and some producers have already begun to do that.

I think there’s just room for everybody, to be honest, with any skills that you have, to be able to do work that would be relevant to this area.

Luisa Rodriguez: Great. OK, so everybody who is listening, who wants to work on this —

Meghan Barrett: Everybody.

Luisa Rodriguez: — there is something you can do, probably.

Meghan Barrett: That’s right.

Insect Welfare Research Society [03:37:16]

Luisa Rodriguez: It also just seems like you are doing a bunch of not just object-level research, but also kind of investing and trying to grow this as a field. And a key thing that you’re doing is running the Insect Welfare Research Society — which, as I understand it, aims to support the global insect welfare research community, and also the incorporation of evidence-based information on insect welfare into policy and practice by these relevant stakeholders. Can you say more about what exactly the Insect Welfare Research Society does, concretely?

Meghan Barrett: Yeah, for sure. So we are a scientific society, so we are mostly geared towards academics, to be clear, and interacting with academics and the field that way. That said, we’re interdisciplinary, so we’ve got philosophers, welfare scientists, entomologists, economists, agricultural specialists, et cetera, involved. It’s just typically academics or independent researchers who are the people that are members of our organisation.

That said, anybody is welcome to become a member of our listserv . We send out a monthly newsletter where we highlight brand new research in the field, either philosophical and theoretical work, economic work, welfare science and empirical work, anything like that that we think might be relevant to the community, as well as opportunities for things like funding or small meetings and presentations, research opportunities, things like that. So anybody’s welcome to sign up for our listserv. You do need to be a researcher of some kind to be a member of the organisation.

We do a bunch of things that you see other scientific societies do to support members of their field. One would be we run a small meeting support programme . This is an awards programme geared at helping people organise workshops and things like that on invertebrate welfare or sentience.

I should say, although we are the Insect Welfare Research Society, we are really the Understudied Invertebrate Welfare Research Society: so kind of anybody but cephalopods — and we might even consider the cephalopods, to be perfectly honest, but they’re by far the most popular invertebrate, I guess I would say, from this perspective — is welcome to contribute. And my guess would be that nobody would actually diss the cephalopod researchers and tell them they can’t come hang. So invertebrates are welcome. Vertebrates, you got your own stuff already going on.

We have annual student research awards in both sentience and welfare that we run once a year. So these are little awards for graduate student research projects focused on those two topics, kind of both a CV line, a grant writing opportunity for those students, and an opportunity to get research done that hopefully promotes the field. This is really common for research societies to do.

We have a research library . One thing we’re interested in doing is providing resources that can help the community and its membership kind of grow in their awareness of the topic, find resources that are valuable for their research, and things like that. Because one problem with insect welfare is that it’s spread out among all these disciplines, and there’s not really been a home for it before. So there’s a surprising amount of relevant literature; it’s just scattered, and finding it can be a challenge. So we’ve tried to bring it all into one place in our research library, which is about 400 studies now on invertebrate sentience and welfare. Again, anybody can search through that research library to find studies of interest to them with keywords that we’ve tagged. So if you’re interested in the evidence, that’s a great place to start.

We’ve created other resources too. So one thing that we created is a power analysis guide that was created by our coordinator of research programming, Dr Craig Perl, who’s a fantastic insect neuroethologist. So this guide is to help people reduce animal use in lab settings by doing some statistics in advance to determine how many animals they actually need to use for a study. This is pretty common practice for a lot of vertebrate research, but not common practice at all for invertebrate research. And this guide is meant to help graduate students who maybe aren’t super statistically savvy figure out how to do this for their studies. So that’s available on our website [along with a second, advanced guide co-created by Dr Colin Lynch and Dr. Craig Perl, on estimating sample sizes by simulation].

Luisa Rodriguez: Super cool.

Meghan Barrett: Yeah, it’s a great guide. He did a phenomenal job making it really understandable and accessible, and just a way to improve our practice as research entomologists.

We have some of the very, I believe, the very first guidelines for protecting and promoting insect welfare in research settings . So we created those. They’re available on our website. We update them every year , and we should be releasing also one on aquatic invertebrates this year, too, for aquatic invertebrate researchers. Dr Andrew Crump actually led that initiative to create that.

We host research seminars every other month that are virtual. They’re open to the public, so you can come listen to scientists and philosophers and economists and welfare scientists talk about their research that they’re doing related to this area.

We do a lot of things like that. We try to connect collaborators, we try to connect stakeholders with experts to assist with their projects. So just connecting relevant parties to make sure that the evidence is really making its way to the people who are going to use that evidence for their work, and that conversations are being steered in an evidence-based way.

And eventually we hope to grow even more than where we are now. We actually started in 2023. We kind of went live in May [2023]. So we’re very new. But our hope is to eventually start holding conferences and small meetings like you see in other kinds of professional societies, once we have enough ongoing active research to be able to support our membership in that way too.

Luisa Rodriguez: That just sounds fantastic. That was so many benefits or offerings. I wasn’t expecting there to be quite so much. Do you need funding? If anyone listening is like, “Ooh, I really wish I could help, but I don’t know anything about insects and I’m not interested in changing my career,” is donating an option?

Meghan Barrett: Yeah, for sure. There’s a donate button on our web page. You can go there. We are 501(c)(3), so for sure. Absolutely, we are happy to accept donations. And we’re also happy if you want to earmark them for particular initiatives. So you want to support our student research awards or something like that, very happy to see that too. Of course, our staffing costs are how we get these things done, so undefined donations are also very welcome.

But I think basically funding just helps us accelerate our ability to achieve particular goals. And accelerating research, I think, is actually really essential right now. So we would be very, very grateful for anybody who considered donating to the organisation, for sure.

Luisa Rodriguez: Before we wrap up, this has been an especially in-depth conversation. So if you wanted someone listening to take away a single thing from this episode, what would it be?

Meghan Barrett: A single thing. You’re only going to give me one thing from the whole episode? That is not a lot of things that I get to share. OK, one thing to take away from this episode, I think what I would say is: don’t trust your intuitions, keep learning. I feel that way about my own journey in this space — that I had intuitions, even as somebody who knows a lot about insects, that have proven not to be very good intuitions in a lot of ways. I also had intuitions about vertebrates that have proven not to be good intuitions in a lot of ways.

And I think this is just a really complicated area. Hopefully we’ve discussed some of that nuance with enough detail that you can see how complicated each and every piece of evidence actually is in the value that it provides to the discourse, what we actually know about consciousness, et cetera. So if you have intuitions about insects, I hope that you’ll consider reaching out to experts or doing a lot more research into the field, instead of trusting those intuitions — because they probably are unlikely to be borne out the way you think they will, and they can be complexified and made more nuanced, and it will be important for your understanding of the plausibility of insect sentience and what their welfare concerns might actually be.

And a great way to do that, of course, would be to join the listserv of the Insect Welfare Research Society or take a look around our research library as ways that you can continue your education over time on this ever-evolving, very novel, complicated, high-uncertainty area.

Luisa Rodriguez: Nice. OK, we’ve got time for one final question. So, this is a very selfish question; I just want to know: what is your favourite insect-related fun fact?

Meghan Barrett: Oh, didn’t I give you so many great insect fun facts?

Luisa Rodriguez: You gave me so many. But I want to know your favourite .

Meghan Barrett: I think what I’ll do is I will give you a non-insect fun fact, because we’ve done so many insect fun facts, and I am constantly sad at how underappreciated all of the other arthropods are. Especially like, the non-decapods, non-insects: the poor myriapods and chelicerates are just so unloved, and there’s no reason for it. They’re so cool.

Luisa Rodriguez: Those poor things.

Meghan Barrett: Those poor things. Am I right? So let’s talk about spider brains for just a minute. I think when I learned this fact about spider brains, it absolutely blew my mind.

For spiders, when you look at their brain, the part of their brain that we call their sub-oesophageal ganglion — it’s named that because it’s below the oesophagus, so sub-oesophageal — it literally looks like a little spider inside of a spider. It’s rad. It’s got little tiny bits that go into each of the legs, and so it’s got like a little eight-legged brain inside of it that I just think is so cool looking. And then it has more little projections for its mouthparts, basically. But yeah, it just looks like a little tiny spider living inside the spider. And this is cool because insect brains actually don’t look like little bees inside bees.

Luisa Rodriguez: How disappointing.

Meghan Barrett: But the spider brain does, which is pretty cool.

Luisa Rodriguez: That is really cool.

Meghan Barrett: Yeah. Give the spiders some love. They can dance. You should look up some videos of spiders dancing. That’s also very cool that they do. And give them some love.

Luisa Rodriguez: That is so cool! And a great way to end. My guest today has been Meghan Barrett. Thank you so much for coming on The 80,000 Hours Podcast .

Meghan Barrett: Thank you so much for having me. I really appreciate the opportunity to just talk at length about all my favourite bug facts.

Luisa’s outro [03:47:01]

Luisa Rodriguez: If you enjoyed this episode, I also recommend our recent episode with Bob Fischer, on comparing the welfare of humans, chickens, pigs, octopuses, bees, and more .

And if you’re curious to learn more about consciousness and sentience in general, I really recommend you go back and listen episode #67 with David Chalmers on the nature and ethics of consciousness .

All right, The 80,000 Hours Podcast is produced and edited by Keiran Harris.

The audio engineering team is led by Ben Cordell, with mastering and technical editing by Milo McGuire, Simon Monsour, and Dominic Armstrong.

Full transcripts and an extensive collection of links to learn more are available on our site, and put together as always by Katy Moore.

Thanks for joining, talk to you again soon.

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#173 – Jeff Sebo on digital minds, and how to avoid sleepwalking into a major moral catastrophe

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#185 – Lewis Bollard on the 7 most promising ways to end factory farming, and whether AI is going to be good or bad for animals

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About the show.

The 80,000 Hours Podcast features unusually in-depth conversations about the world's most pressing problems and how you can use your career to solve them. We invite guests pursuing a wide range of career paths — from academics and activists to entrepreneurs and policymakers — to analyse the case for and against working on different issues and which approaches are best for solving them.

The 80,000 Hours Podcast is produced and edited by Keiran Harris. Get in touch with feedback or guest suggestions by emailing [email protected] .

What should I listen to first?

Check out 'Effective Altruism: An Introduction'

Subscribe here, or anywhere you get podcasts:

If you're new, see the podcast homepage for ideas on where to start, or browse our full episode archive .

IMAGES

HUMAN CENTIPEDE DRAWING EXPERIMENT
Creating A Human Centipede: Is It Medically Possible?
The Human Centipede (First Sequence) (2009)
First Peek: The Human Centipede 3 (Final Sequence)
10 Terrifying Films About Experiments Gone Wrong
The Human Centipede (First Sequence) (2009)

COMMENTS

'The Human Centipede' Was Inspired by Nazi Experiments
Is 'The Human Centipede' Based on a True Story? During the Nazi reign of Germany, some incredibly questionable doctors and surgeons were performing experiments on victims in concentration camps.
Nazi human experimentation
Nazi human experimentation was a series of medical experiments on prisoners by Nazi Germany in its concentration camps mainly between 1942 and 1945. There were 15,754 documented victims, of various nationalities and age groups, although the true number is believed to be more extensive. Many survived, with a quarter of documented victims being ...
True story behind The Human Centipede
The iconic Dutch horror film The Human Centipede by director Tom Six was released in 2009 and produced some rather visible reactions. ... The experiments saw prisoners across Europe forced to ...
The Human Centipede (First Sequence)
The Human Centipede (First Sequence) is a 2009 Dutch independent body horror film written, directed and co-produced by Tom Six. ... His prior experiment, the 3Dog, conjoined three Rottweilers into a "Siamese triplet"; all three dogs died following the operation. Heiter has moved on to using human subjects.
Was The Human Centipede Real? From Horror To Reality
The human centipede was inspired by horrific Nazi experiments shared by survivors of concentration camps, but it is not exactly as depicted in the movie. Scientists and surgeons in Nazi Germany were performing inhumane and unethical experiments on victims in concentration camps.
True story behind The Human Centipede
The Human Centipede 2 (Full Sequence) The sequel film took things to an even darker place, with much more graphic scenes and more disparate inspirations. Six decided to make the plot very meta: it would focus on a fan of the first film who would then conduct his own sadistic experiments and punishments.
The Human Centipede (First Sequence) (2009)
The Human Centipede (First Sequence): Directed by Tom Six. With Dieter Laser, Winter Williams, Ashlynn Yennie, Akihiro Kitamura. A mad scientist kidnaps and mutilates a trio of tourists in order to reassemble them into a human centipede, created by stitching their mouths to each others' rectums.
The True Meaning Of The Human Centipede Movies
The Human Centipede movies do contain some meaning, even if the delivery is a little hard to stomach. ... There is no stated reason for his experiment. Audiences who saw "The Human Centipede" were ...
The Story Behind The Human Centipede
The Human Centipede (First Sequence) marks Williams' first lead role in a feature film, the 26-year-old having previously only appeared as a Nelwyn villager in fantasy Willow .
The True Stories Behind the Human Centipede
These were the sort-of true stories of Human Centipede-like experiments. These experiments put a gruesome crown on a time that was already abhorrent to the global populace. A lot of the tests resulted in injury, disability, trauma, and death for the unfortunate and unwilling participants. Some experiments were carried out on twins, who were ...
True Story Behind Human Centipede
The Nazi experiments revealed the darkest side of human nature, and today we're going to look at one of the most insane experiments that inspired one of the ...
Saw, Hostels, Human Centipedes: A history of torture porn
Saws, hostels, and human centipedes: A long and unpleasant history of torture porn. By. Clark Collis. Published on January 28, 2020 07:45PM EST. In the aughts, horror movie characters were ...
'The Human Centipede' Was Inspired by Nazi Experiments
Directed by Tom Six, The Human Centipede is a trilogy of films — released in 2009, 2011, and 2015 — widely known as depraved and well, icky. It's the story of three people trapped by a deranged German surgeon after their car breaks down.
The Human Centipede: First Sequence
The disagreeable creation at the center of Tom Six's "The Human Centipede: First Sequence," a beyond-twisted body horror experiment in which a mad surgeon, renowned for separating Siamese ...
The Human Centipede (First Sequence)
The Human Centipede (First Sequence) By. Owen Gleiberman. Published on April 30, 2010 04:00AM EDT. There's a certain breed of horror-film junkie who craves the extreme (I know, I'm one of them ...
[Interview] Tom Six Reflects On 10 Years of 'The Human Centipede' and
It is surreal that the first Human Centipede is celebrating its 10th anniversary this year. I vividly remember hearing about the film for the first time back in 2009, talking with friends about ...
Creating A Human Centipede: Is It Medically Possible?
In 2009, Dutch filmmaker Tom Six introduced the world to a whole new meaning of the term "ass-to-mouth" when he released the now-cult horror classic The Human Centipede: First Sequence, about a German surgeon known for separating conjoined twins, who, in retirement, developed a sick fascination with recreating those junctions.He captures three tourists and creates a "Siamese triplet ...
THE HUMAN CENTIPEDE
Truly one-of-a-kind, Tom Six's twisted biological horror film THE HUMAN CENTIPEDE confidently goes where few films have dared to go. The sick vision of a dem...
Anatomy of a Gimmick: The Human Centipede, "the Most Horrific Film Ever
Filmed in Holland, The Human Centipede: First Sequence is set in the sterile, modern home of a crazed surgeon, Doctor Josef Heiter (Dieter Laser), whose Nazi-inspired human experiments take place in a clean, well-organized surgical theater with little on-screen blood or guts. The centipede itself is also unexpectedly well-kempt.
10 Years Of 'The Human Centipede' And Its Prediction Of The ...
Not the good guy. IFC. For a movie that only grossed $252,207 worldwide at the box office, The Human Centipede, which turns ten years old today, is a movie that has had an outsized cultural ...
The Human Centipede II (Full Sequence)
The Human Centipede II (Full Sequence) Dutch-born writer-director Tom Six is a man of his word, and his promise to make a far grosser follow-up to his 2009 horror hit is more than fully realized ...
Mad Surgeon Experiments Human To Make A Real Life Human Centipede
Two American girls are on a road trip through Europe. In Germany, they end up alone at night and when their car breaks down, they take shelter in an isolated...
Meghan Barrett on challenging our assumptions about insects
Other human uses of insects: ... they could weigh 50 kilogrammes. We're talking myriapods — that's a millipede or a centipede today — and they would be taller than me; they'd weigh as much as I do. ... So researchers have done experiments where insects are given anaesthetics or analgesics — like opioids, drugs that reduce anxiety ...

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The Big Picture

The Human Centipede (First Sequence)

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Roger Ebert Simply Refused to Rate ‘The Human Centipede’

‘The Human Centipede’ Was Also Inspired by a Joke

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