Image: Female earwig guarding a clutch of eggs (Source: Marshal Hedin on Flickr; used according to CC BY-SA 2.0 license).

Our new episode is available from our Podcast host here: https://asabpod.podbean.com/e/episode-65

Transcript

Charles 0:00
Fluid oozing out of the female’s abdomen and the nymphs all feeding on that fluid.

Tessa 0:07
That’s not too different from mammals

Charles 0:10
I literally have in my notes. Is that really that different from lactation?

Charles 0:15
[Theme Music]

Charles 0:39
Hello and welcome to Assigned Scientist at Bachelor’s. I’m Charles and I’m an entomologist.

Tessa 0:44
And I’m Tessa and I’m an astrobiologist.

Charles 0:47
So I thought what would be interesting for Mother’s Day is to specifically talk about a couple of examples of maternal care in insects. And I think to introduce the topic – really why I think this is interesting is that insects are a group of organisms which very rarely show really dedicated parental care, as in care of their offspring after laying eggs. Insects overall are a very good example of r-selected organisms and Tessa, if you go to remind the public?

Tessa 1:19
So there is an idea amongst biologists that you can, very broadly speaking, divide organisms up based off of their reproduction strategy. You have are selected which produce a whole mess of offspring, hundreds, potentially, but don’t really invest much care in them. Basically, you lay your eggs, and then they’re on their own, or K selected, where you only have a few offspring, but you invest a lot of time and care into them and making sure that they make it to adulthood.

Charles 1:51
It’s basically the idea that you have, like, a certain amount of resources that you can invest and so on one extreme end, you can produce a lot of offspring, but many of them are probably going to die because you aren’t taking care of them, or you can produce a couple of offspring, but really invest a lot of time and energy and resources into them, and then maybe, you know you’re having less overall, but more of them are reaching adulthood and reproductive maturity.

Charles 2:18
And so in insects, typically, the strategy is you’re producing a lot and most of them are gonna most of them are gonna die. But it’s fine, because some of them won’t. Pursuant to that, active maternal care in insects is interesting because it’s so unusual. And even among those insects which invest more energy into each offspring individually, much of the time, it might be an example, like some parasitoid wasps, which may lay eggs one by one in kind of prime real estate, but once the eggs are laid, then the actual parental investment is essentially non-existent. So I have come up with three examples that I love to discuss, and I have placed them in order of how strong I think they would be as a metaphor for motherhood, if motherhood is unending sacrifice until you die.

Charles 3:15
So to begin with: egg guarding, which is reportedly the most common form of post egg laying parental care in insects, and specifically I want to talk about egg guarding in earwigs. “Earwig” is the common name given to members of the order dermaptera, and I think dermaptera are one of those insects that are pretty common, including in human habitation. So if you showed most people a picture of an earwig, they’d probably go, Oh, I’ve seen those, but they probably wouldn’t recognize them just by name, like if I just said Dermaptera to a random person, like, I don’t particularly know what that is, but probably their most recognizable feature is that they have these really big, noticeable cerci.

Charles 3:54
And cerci are just sensory organs that project out of the end of the abdomen, or the butt area, of the insect. And a bunch of different insects have… it’s a highly variable morphological feature of different insects because they are sensory organs. So like different groups of insects, some have really long ones, some have really short ones, et cetera, et cetera. And in earwigs, they exhibit a form of sexual dimorphism where male earwigs have cerci that look like really big, sharp pinchers. So as far as we, as in humans, know, all earwigs exhibit some degree of maternal care. And I say as far as we know because, as any given entomologist will tell you on any given day, we know, probably a fraction of the total insects on Earth, and most insects, even that we have described taxonomically, we don’t actually have any ecological or behavioral data about them.

Tessa 4:51
Right.

Charles 4:52
So it’s possible that there are earwigs in the world that don’t exhibit maternal care, but apparently not, not in scientific documentation up to this point, and the degree of investment that they exhibit is highly variable between species going from just guarding eggs after they’re laid to guarding and cleaning eggs to even sticking around after the eggs have hatched in the first couple stages of the nymphs lives. And specifically, I would like to tell you about the species, Anisolabus maritima, or [different pronounciation, more like “maritime”] maritima, probably maritima. But also all scientific names are fake. They’re not real words. Also apparently known as quote, the maritime earwig. And as you may be able to guess from the name, these earwigs are found particularly in environments that are close to an ocean. When laying eggs, females will excavate a little nest, often under driftwood or under rocks, and lay a clutch of eggs. And as they lay eggs, the way that these guys do it is that they lay a single egg at a time. This can take place over a period of a couple of days.

Tessa 5:58
Which is a long time, especially for insects.

Charles 6:01
Yeah, if you’re an earwig, that’s a big chunk of your life. This laying over a period of several days is in contrast to some insects, like mantises, for example, which produce an ootheca that has all their eggs altogether, and they lay them all in one big bunch, and then they go die. Because mantises, they hatch in the spring – at least in temperate environments, like most of the so called United States – they hatch in the spring. They grow, grow, grow, grow until the fall, they find each other, they mate, they lay an egg case, and then when it gets cold, they just die. And the way that they overwinter is in the egg case. And then the new mantises hatch in the spring, and then life keeps on going, etc, etc, etc, you know the drill.

Tessa 6:38
Yeah.

Charles 6:39
And so these earwigs. Specifically, this species stays with their eggs throughout the whole period of them being eggs, and then for the first two instars after they hatch. And without getting exhaustively technical about it, instar is the term used for periods between molts and insects. So when they hatch, they’re in their first instar. And then after they molt, the first time, they’re in their second instar, where, obviously vertebrates like you and like me, as far as you know, we grow pretty continuously and gradually, whereas insects and other arthropods, they go through sort of step wise growth until they get to their final molt. This is specific to insects. They get to their final molt. And the thing that they get in their final molt when they’re adults is they get genitals and they get wings. So if you see an insect that has wings, that’s an adult.

Charles 7:28
All of this is to say that, saying that the earwig, the mother earwig, stays with their young through the first two instars. It just means they stay with them all the time, that they’re eggs, and then they hatch, and then they molt once. And then after the first molt, when they’re in their second instar, that’s when the mother earwig leaves their lives. And so Multiple studies have been done looking at the effect of maternal care, i.e., egg guarding and cleaning on hatching success in ear wigs, and they have found, probably unsurprisingly, that it has a very positive effect, as one of the authors of the papers I read put it quote, life history theory predicts that parental care evolves when the benefits of care outweigh the costs to future reproduction. And in general, when we talk about the evolution of traits, we often say that energetically costly traits or behavior wouldn’t stick around in populations if they weren’t providing some benefit overall.

Charles 8:14
Yeah, another thing I want to note from this one study I read called “Parental care trade offs in the role of filial cannibalism in the maritime earwig Anisolabis maritima,” is that they had an experimental setup with a bunch of different options, like nests with and without mothers present with and without, cages to keep predators out in the field and in the lab and in all cases, the success rate for hatching eggs was never particularly high. And this isn’t really specific to the idea of maternal care, but it does remind me of something that I’ve been thinking about a lot, just how incredulous a lot of people, maybe most people, are about the omnipresent specter of death hanging over all living organisms. We’re all surrounded by the possibility of death at all moments of our lives, and as it was with humans in 19th century hospitals where doctors refused to wash their hands, so too is it for your average earwig.

Charles 9:10
But then also, this study looked at the infection rate of eggs and found that those with mother earwigs got infected substantially less. The infection rate being much lower in cases where that eggs were kept with a mother earwig was interpreted as reflective of how earwigs will clean off of the eggs in their clutches a lot of the time, thereby protecting them from infection. And another study called parental care alters the egg microbiome of maritime earwigs speculated that mother earwigs have themselves bacteria that could convey antifungal protection to their eggs, and they didn’t like identify specific bacteria that might serve that role in the eggs, but they did also find that cleaning behavior from female earwigs changed the egg microbiome. And so all together, that you know, indicates that maternal care is very important here, both in protection in general and in protection from predators, but also in production from infection, where the mother earwig in the you know, will stay with the clutch of eggs and clean them off and then prevent that fungal infection.

Charles 10:10
And another study found that progressive provisioning after hatching, ie the earwig going out, getting food and bringing it back further increased survivorship. And so you’ll notice, I’ve placed this first on the list of like, how apt or powerful a metaphor for motherhood. I thought this would be. And you might think, well, this seems like a great example of motherhood. The earwig lays the egg, stays with the eggs, guards the eggs, protects the eggs, cleans the eggs, and then even hangs around after the eggs have hatched. Like it’s a full sort of a full service, you know, parental protection situation. And it’s true.

Charles 10:45
But this species has also been well documented practicing filial cannibalism, i.e. eating their own eggs, because it, you know, one of these studies provided several hypotheses about why the earwig would eat the egg. For instance, if they laid too many eggs and they couldn’t take care of all of them, eating some of them, then offers some control over how many they have to take care of staying with the eggs, then reduces the resources that the parent earwig has access to because they’re staying with the clutch of eggs. So an egg is as we all know from eating eggs as humans, eggs are a great source of nutrition. They didn’t necessarily find support for that hypothesis, but they did also document there were cases where they would just be like, I’m actually not gonna, I’m not gonna take care of this one, and then they would just effectively abort the clutch by eating all of them. So I’m placing this one first on the list, because that’s behavior that we that’s generally frowned upon.

Charles 11:50
So then the next, the next example I have is moving on from earwigs to my favorite group of insects, which is, of course, cockroaches. And I don’t want to talk about the whole range of reproductive strategies and cockroaches, because that would take hours, if not days. But a lot of it comes down to different strategies related specifically to ootheca or to their oothecae, which are their egg cases, which, as we have discussed before, often look like little leather clutch purses, and you see this huge variation, where you have some cockroaches which will lay the egg case fully outside of their own body, and oftentimes they will conceal it somewhere, or they’ll bury it, but then they won’t take care of it after that. And then whatever happens, happens. And then there are some cockroaches which will produce the ootheca, but it’ll be mostly hanging out of their abdomen, but partially, but still connected to the back of their abdomen. And the part that’s still inside their body will often have like, more membranous material, so that there’s a passage of nutrition between the egg case and the cockroach, and then you have some which extrude the whole egg case and then suck it back up into their body.

Charles 13:04
And then you have examples where the eggs are never laid outside of the body at all, they’re all laid directly from the oviduct into the brood sack and then kept in there. And there’s one example that I can find of what is deemed not ovoviviparity, but just viviparity. There is one species that has been described, Diploptera punctata, which are described as viviparous, and the eggs are laid directly into the brood sac and are supplied with, quote, “A proteinaceous fluid secreted by the mother.”

Charles 13:35
And so, one source I read suggested that some people consider all this range of like egg case treatment, parental care, since it is an investment by a parent after fertilization, which is not the case in EG mantises, which, as already mentioned, fertilize eggs, produce an Utica, attach it to a twig somewhere, and then bounce. Whereas cockroaches, except in the cases where they just lay the egg case, and then leave there is some ongoing investment in protection or in nutritional supply, etc, to the egg case. But I don’t want to talk about that. I feel like we’ve already talked about it at length, and we’ve also talked about how that one cover of the Animorph book, it’s a Marco perspective cover, and it shows him morphing into a female with an egg case. And my thing is like, I think the guy who did the covers just didn’t think about it that hard, because I think that goes against what we know about morphing. But at the same time, I realize that that doesn’t matter. I realize that it doesn’t matter.

Charles 14:34
Moving beyond that, moving beyond the idea of parental care as just ongoing investment, but specifically caring for and investing time and energy and presence and nutrition into offspring after they have been laid as eggs and after they have hatched as eggs. There’s one specific example that I wanted to bring, which is the species Thorax porcellana, which is a beautiful light brown speckled roach found in Southern India, and about which there was not a lot of information published. Thorax porcellana really has a couple of studies that are available to us, at least in English. We do know that they exhibit a relatively unusual behavior in insects, which is that during the first and second instars, ie the first two stages of post hatched life cycle of the nymph. The species nymphs all cluster together under their mother’s wings. So most cockroaches are very flat. This is one of the things that people know about cockroaches. They’re flat and they’re round and they’ve got long antennae. And most people think that they’re very gross, but my argument is that they’re not very gross. I feel like, spiritually, I have a lot in common with, like, rat people, people who really love rats.

Tessa 15:46
Yeah, yeah. Similar stigma.

Charles 15:48
Similar stigma. That’s what most people know about cockroaches, and in Thorax porcellana, instead the four wings, instead of just being flat against the abdomen, are kind of domed, and then the abdomen itself can kind of depress so that it creates a little bubble of space, so all the nymphs, after they hatch out of the egg case, cluster together underneath the wings of their mother cockroach.

Tessa 16:13
Oh, they get a piggyback ride.

Charles 16:14
They get a piggyback ride. And this is very cute to start out with, but wait – another interesting feature is that the hind wings of the females are also reduced. So most insects have four wings and two sets of wings, the four wings and the hind wings. And there are a couple of orders which are characterized by only having a single set of functional wings, notably Diptera, the true flies, and Strepsiptera, the quote, twisted wing parasites, which almost universally demonstrate really pronounced sexual dimorphism, where the males are free flying and the females are endoparasitic. So most insects have four sets of wings, and these cockroaches also do. I don’t know of any cockroaches who, other than just fully apterous cockroaches, who don’t develop wings in adulthood at all. In Thorax porcellana it is not any of these normal cases of reduced or absent wings. Because also in a lot of cases, you see insects that have secondarily lost their wings, which is just something that we say in evolutionary biology, to say that ancestrally, like their ancestor, had wings, and then at some point they stopped having wings. Because, as already mentioned, if something is very energetically costly and it’s not providing any benefit, then it will typically be lost as a characteristic. So like stick insects usually don’t have wings, or they have very small wings because those guys aren’t flying around. They’re too busy looking like big sticks.

Tessa 17:35
Sticks aren’t known for flying. It kind of defeats the purpose if you then start flying.

Charles 17:38
So all of that to say, to point out the uniqueness of this characteristics, where Thorax porcellana females, their hind wings are reduced specifically so that there is more room underneath the fore wings for all the little nymphs. And it’s, it sounds very cute if you’re a cultured and sophisticated modern person who appreciates that cockroaches are very cool and very beautiful. But I’m putting this example in the middle, in terms of sacrifice, both because having 40 offspring on your back all the time would be annoying, but also because, as far as the research that we have so far indicates, the way that nymphs feed while they’re all clustered together under their mom’s wings and their first two instars is that, quote, “The dorsoventral compression of the body of the mother forced the flow of body fluids to ooze through the dorsal pores and the openings on the turgum made by the nymphs with the help of their sharp mandibles.” In other words, the flattening that has to happen to make space for all the nymphs, as well as the nymphs themselves, probably biting produce a case of fluid oozing out of the female’s abdomen and the nymphs all feeding on that fluid.

Tessa 18:46
That’s not too different from mammals.

Charles 18:50
I literally have in my notes, is that really that different from lactation?

Tessa 18:54
Yeah.

Charles 18:55
And it’s like, who’s to say? Both of them are kind of a nightmare to me, but so this one goes in the middle because the mother roach doesn’t die and doesn’t seem to particularly suffer any like real setbacks, necessarily, in terms of, you know, they’re not sacrificing their own body to feed their young any more than like most individuals who feed their their offsprings on their own body fluids do, but like, I don’t know about you, but I would not like 40 offspring clinging to my back and also drinking my abdominal fluids.

Tessa 19:26
Yeah, yeah. 40 is a lot.

Charles 19:28
And according to one source, this lasts for seven weeks, which like in the course of my life, if I had that happening to me for seven weeks, I would be very irate about it. In the much shorter lifespan of a cockroach I can’t even imagine.

Charles 19:48
Finally, we come to my last example, which is I would love to tell you about strep ciptera, which I’ve already mentioned, and which are known as the twisted wing parasites, although sometimes I see these so called common names for insects, and it’s like, is this name actually common for anybody who’s not also just going to know the name Strepsiptera? Not everybody knows the term Hymenoptera, but they know bees, ants, wasps and sawflies, whereas, like, if you know enough about insects to know the term “twisted wing parasite,” you probably already just know the name Strepsiptera.

Charles 20:21
Strepsiptera almost universally demonstrate a really extreme form of sexual dimorphism, where the males as adults are free flying. They’re flying around. They got a set of wings. They’re hanging out for about a day, and then they die. But whereas females in all but one family are parasites on mostly other arthropods. There’s some that are parasites mostly on bees and wasps, and then others that are parasites mostly on bugs. I’ve collected organisms, both from the true bugs and wasps, and then later discovered on you know, further examination, that they had little strips of dracephalothoraxes hanging out. And it’s always so thrilling. It’s very exciting.

Charles 21:03
So, you know, the adult males are free of flying. They have a single set of functional flying wings, which are sort of large and wrinkly looking, and that’s where the twisted wing comes from. And then the parasite part comes from the females, who are parasitic within the abdomens of other insects. And they have these massively reduced bodies. They’re basically shaped like a kind of a tube, and they have a hardened cephalothorax, so just a head and thorax kind of all bunched up together in one segment poking out between the overlapping segments on the abdomen of their host and then the rest of their body. They have a very thin cuticle through which they like absorb nutrients and stuff. And I was thinking about Strepsipteran the other day, and I was like, I don’t actually know what their pre adult life looks like. I looked into this, and I there are some very detailed embryological descriptions of strep siptera, but I couldn’t find a lot of like, detailed, well sourced information on their actual life history in early stages, and so I almost didn’t include them, because I was like, I don’t, I don’t like to give information to our listeners that I can’t provide really clear sourcing for, but it’s just too good that I’m still including it.

Charles 22:18
But with that caveat, and I basically saw some sources which did not provide good citations describing members of at least one subgroup practicing what they called hemocellus viviparity, where basically the eggs get fertilized and then they hatch inside the Female strepsipterans body and eat their way out. I wanted to end on that, if that’s not exemplary of motherhood, I you know, I don’t know what is, which I guess tells you a lot about my feelings, about what parenthood must, what parenthood must feel like.

Charles 22:56
Because I also do want to, I was thinking about this earlier. I have pretty uncomplicated relationship with my mom. I feel like, I don’t really know in specific, Sesa, but I feel like you have a good relationship with your mom.

Tessa 23:12
Yeah, yeah.

Charles 23:13
But I was thinking about this earlier, and I was like, I mean, the thing about this is I would imagine that probably, I mean, I haven’t done a demographic survey, but I would imagine that probably a lot of our listeners are also trans. It would be shocking to me if we had like, a cis majority listenership, like, I don’t know how they would have gotten here, but if there’s any group of people who, on average, have a very complicated, if not outright acrimonious relationship with their mothers, it’s, you know, it’s trans people by and large. So I do. I just, I just wanted to include a note if you hate your mom, if you’ve been disowned, or you have disowned your mom, I don’t really have that’s, I’m sorry, and I hope you take some solace in that the strep cipter and mothers, they just get eaten, and maybe there’s some catharsis there for you, but basically, I just wanted to acknowledge that, like, Mother’s Day is probably a pretty fraught day for a lot of the people who listen to this podcast, and that sucks. And that’s my that’s my conclusion. It sucks terrible when parents don’t support their kids. Terrible when parents don’t support their trans kids.

Tessa 24:25
Parents should be more like the insects that we’ve covered.

Charles 24:27
I feel like Thorax porcellana is like a nice middle ground… because I didn’t see any reports of cannibalism there. I mean, it’s not impossible.

Tessa 24:35
Yeah, it’s nice middle ground.

Charles 24:36
Nice middle ground, because this is the other thing, is that I think people don’t really realize how unspectacular and commonplace cannibalism is like in the animal kingdom. A lot of animals just eat, they just eat each other, and sometimes the each other that they eat are members of their own species, and that’s life. I also am one of those people who I feel like there’s morally in … if you’re, like, in a survivorship situation and somebody’s already dead, and if you don’t eat them, you’ll die.

Tessa 25:05
Oh, there’s precedent for that. Actually, it’s sometimes referred to as the law of the sea.

Charles 25:09
Well, even outside of, like, even putting aside legal precedent, just morally it’s, I guess what I’m saying to you, Tessa, is that we ever get if we ever get stranded in the mountains and I just die, like, just unavoidably, and then you have to eat me to keep living. I like, I want you to do that. I don’t want you to die.

Tessa 25:28
I appreciate that, yeah, and likewise.

Charles 25:31
I appreciate that. And that’s friendship,

Tessa 25:33
Excuse me, it’s not the law of the sea, it’s the custom of the sea, but yes.

Charles 25:38
That gives you a really harrowing just like image of historical sea voyages, I think.

Charles 25:47
So if people want to find me, I am on Bluesky, chwallace.

Tessa 25:54
Tessa, where can the people find you? I can be found on Bluesky @tessafisher.bsky.social, and also@tessafisher.com

Charles 26:03
The podcast is on Bluesky at asabpod and at our website, asabpodcast.com. If you want to get in contact with us, you can do so through the contact form on the website or at asabpod@gmail.com. Thanks to Nicole Petkovich for our theme music.

Tessa 26:25
And until next time, keep on science-ing.