We just published an interview: Meghan Barrett on challenging our assumptions about insects. Listen on Spotify, watch on Youtube, or click through for other audio options, the transcript, and related links. Below are the episode summary and some key excerpts.

Episode summary

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

Highlights

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.