Science Friday - Moth Survival Strategies And A Rodent Thumbnail Mystery

Episode Date: October 7, 2025

If you’re a moth trying to stay uneaten, there are competing strategies. Some moths rely on camouflage, trying to blend in. Other moths take the opposite approach: They’re bold and bright, with colors that say “don’t eat me, I’m poison.” Biologist Iliana Medina joins Host Flora Lichtman to describe a study that placed some 15,000 origami moths in forests around the world to investigate which strategy might work best. Then, mammologist Anderson Feijó and evolutionary biologist Rafaela Missagia join Flora to dive into another evolutionary conundrum: why so many rodents have thumbnails. Guests: Dr. Iliana Medina Guzman is a Senior Lecturer in the School of BioSciences at the University of Melbourne in Australia.Dr. Anderson Feijó is a mammal curator at the Field Museum in Chicago. Dr. Rafaela Missagia is an assistant professor at the University of São Paulo in Brazil.Transcripts for each episode are available within 1-3 days at sciencefriday.com.  Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

I'm Flora Lichten, and you're listening to Science Friday. Today in the podcast, from wingtints to toenails, how evolutionary success is in the details. We've found that the answer was very complicated more than we thought. If you are a moth trying to stay uneaten, there are competing strategies around camouflage. Some moths try to blend in. They're drab. They go for earth tones. Other moths take the opposite approach.

They're bold and bright with colors that send the message, Don't eat me, I'm poison, I swear. But which one of these winged wardrobes works better? Writing in the journal science, researchers report on a study that involved placing about 15,000 fake paper moths and forests around the world to see what they could deduce about coloration. Here to talk about it is study author, Dr. Ileana Medina. She's a senior lecturer in biosciences at the University of Mnese.

Melbourne. Ileana, welcome to Science Friday. Hi, Flora. Very nice to be here. We got to start in the methods today. 15,000 origami moths. Please talk me through how you did it and why you did it. Yes, so 15,000 moths could only have been done by lots and lots of people.

So it was a very, very big collaboration and tons of hours of work by many, many other researchers. And yeah, this couldn't have happened without that. really. So yeah, we had teams essentially in all the 21 locations that were placing around 700 of those moths in each of those locations. Still a lot of moths, I would say. 700 to be responsible for 700 moths, that's a lot. Please walk me through the logistics and tell me what they look like. So they are very basic triangles made out of paper, really. We have three different types of targets.

So we have a black and orange one that's meant to represent the classic warning colors that we see in nature, the most common ones. Then we have a black and sort of gray blue, which is an uncommon type of warning color, but that it's equally bright and equally contrasting as an orange one. And then we have a cryptic type of target that is essentially a brown that blends in really well with most of the bark of the trees around the world. And by cryptic, you mean camouflage? Yes, exactly. Yes. I mean camouflage. So a color that blends in really well with with backgrounds. And then we baited these paper moths with a mealworm, essentially to test whether predators were

interested in attacking this particular target or not. Could the origami moss pass for real moths? Did that matter? Yes, that's a very good question. So we went with this experiment because we knew that it worked before. So there's been smaller, more localized trials of this sort of experimental design before. So we knew that the birds would be attracted to those mods. And the truth is that a lot of animals don't have the great visual acuity that we have as humans. So they would need to be very, very close. to something to actually tell that it's not a real moth. Okay. What was the question you were trying to answer here? We were trying to answer under which conditions each of those two strategies would be favored in nature. So as you mentioned, those two strategies being hidden, camouflaged, or being warningly colored. They have evolved many times in, you know, in snakes,

in amphibians, in moths, even in newlybranks. So we were interested in, in understanding, yeah, under which conditions, which of those strategies would be favored. What did you find? We found that the answer was very complicated more than we thought. As always. So the first thing we found is that there was no overall best strategy. So the success of each of those strategies completely depends on the context and the type of environment in which the strategy is happening.

The other thing we found is that predators play a very big role in determining which strategy works best. And essentially, one of the cool things that we found was that the intensity of these interactions and how much predation there is in a forest really affects how likely predators are to go for those warningly colored moths and essentially just bypassing the defense and just go for it. pushed by competition to try those things that otherwise they wouldn't normally try. So if you're a bird and you're living in a place where there's lots of other birds competing with you for dinner, you're more likely to try the brightly colored warning sign moth? Exactly. Yeah, yeah, yeah. That's what we think is happening. Competition would push

these predators to try anything, essentially. I mean, are some birds bigger risk takers than others? Yeah, that's hard to say. I think there's a lot of variation and there's a lot of differences in boldness between birds, but there's definitely some birds that have sort of higher cognitive abilities, like ravens and things like that, you know, that would probably behave differently from something much smaller. How did the camouflaged moths fare? Did you learn anything about about that strategy? Yeah, so we found that the camouflage strategy, the success was highly dependent on the context

and things like the illumination. So forests that have very high, light levels that were very bright in those forests, that camouflage strategy would do worse. And it would also be affected by how common that type of hamleth prey is in a forest. So essentially, if it was forest where the predators were very used to seeing lots of other camouflage prey,

then they would do worse. And we think that happens because predators can form search images and essentially get really good at finding a specific type of prey, even if they are camouflaged. Some of the moths in your study were this vibrant, kind of unnatural blue color. How did they fare? Were the birds freaked out by them? Yeah, that was an interesting.

finding as well. So we use that blue and black color mainly because it is rare, as you say. So in nature, not many species have that particular combination to advertise that they are, you know, toxic or just distasteful. That's quite rare. And then what we found is that that familiarity with the colors matters. So those type of prey did actually poorly in places where the predators were used to the common, you know, red and black and orange and black warning signals. If there were lots of those signals or, you know, butterflies with those types of colors in a community, then the moths with this uncommon pattern, the blue and black would do worse. So familiarity with the signal is important.

And that helps us understand really why so many species use exactly the same. colors across the world and across communities. Those colors work well. And if they already exist, then, you know, the prey is going to do better because predators are already trained to avoid it. That's interesting. Do you feel like this is the definitive moth coloration experiment? Like, we're done?

No. I don't think that really ever happens in science. But I think it was, you know, it teaches us. lots of things, just that, you know, trying to compare different factors in the same study and trying to understand how all those factors interact that brings us closer to understanding how that happens, which is impossible to do, you know, with the smaller-scale studies. And just the power of collaboration to, just knowing that we can, you know, do things like this because there's lots of researchers around the world

that are interested and keen to participate. Yeah, how many countries were you in? I think we were in, this was in 16 different countries and 21 locations. Amazing. Do you think the results generalizable to other creatures beyond moths? You know, snakes or frogs?

Yeah, I think so. I mean, some aspects of it. So, you know, things like the light. the effect of the light on the camouflage, that is something that had been already been sort of down in different smaller scale studies. And then I think that definitely would apply to a lot of other animals that use camouflage as a strategy. And yeah, like certain things, I think that are related to the learning of predators would apply again to other types of animals. Yeah, so I think that there's generalizations, but there's also different.

differences and things to consider when we think about expanding our conclusions to other groups. So other taxa, you know, might use their colors for different types of things as well, not only as an antipredator depends. So that's important to consider. Iliana, thank you so much for joining me today. No worries. Thank you so much for the questions. Very happy to chat. Dr. Ileana Medina is a senior lecturer in biosciences at the University of Melbourne. Don't go away because after the break, we take a look at your nails. Well, actually, the thumbnails of the rodent nearest to you.

If you show a hand of a rodent, most people, they would not guess who's a rodent hand. Stick around. You hear a lot about a superpower of primates, the opposable thumb. It helps us grip and grasp and hold. But it turns out that among rodents, the special appendage upgrade is slightly different. I give you the thumbnail. Researchers dug into the science of the thumbnail and argue that in part it's what helped make rodents so successful. Joining me now to talk about it are two authors of that paper.

Anderson Fejo is a mammal curator at the Field Museum in Chicago, and Rafael Missagia is an assistant professor at the University of Sao Paulo in Brazil. Welcome to you both to Science Friday. Thank you for having us. Yeah, thank you. Okay, why would you want a thumbnail instead of a claw? Yeah, sure. Basically, a nail allow you to have more dexterity in the finger that have the nails. So the claw would grow over your fingertips and will kind of get in a way. So by having a nail, you have more space to have a very high dexterity on those fingers.

So that's why, for example, primates are so good in using tools, among other things. We believe their nails were an important factor, and allow them to have a very good dexterity and handling. I just wanted to add the tip of our fingers and rodent fingers are very vascularized. So they are very useful for tactile sense. They are not opposable, but they use in a way to manipulate food. So they are not opposable as primates, but they do have this combination of two terms to be able to do

the manipulation. What's the evidence for thumbnails being the secret sauce for rodents? I mean, is this an evolutionary history story? Yeah. So another big find of your study was that nails on rodent's thumbs are actually very ancestral state. And we found it for very high confidence that the ancestral, going back 55 millions ago, already had nails on their thumb. So for us, that shows that taminails were present across most of the rodent evolutionary history. One of the reasons to explain how rodents become so successful and one of the most common mammals in the world was because they were able to utilize and consume seeds and nuts. And this is a very hard resource to access.

If you think about like an acorn or another kind of nuts, is a very hard shell outside that basically prevent all the animals to consume. But rodents were able to access this resource. And before, basically, the specialized teeth were the main

factors associated with that ability to access those foods. But we're now saying that in addition to have special teeth, specialized muscles, the ability to hold their food with their thumbs. And in that case,

the plays a key role and allow them to have this dexterity is another key piece of the puzzle to explain how they are able to access those resources and because of that evolve in different groups in different environments. I'm thinking of Darwin's beaks, you know, this is just a variation. This is another tool that they use, that they're sort of an adaptation to get at the food they need. Yes, exactly.

It's pretty much a similar scenario. Do all rodents have thumbnails? So we found that approximately 85, 86% of species that we analyze have nails, which is a big portion of rodent diversity. But the interesting thing is that most of them have nails and do food manipulation. That's as Anderson said, it's an ancestral condition. Most rodents are like that. But we have some exceptions that appear many times.

So one of the exceptions is that we have rodents that don't have anything at all. They don't have nail or claw. So they don't handle food. They eat orally just as cows. One example is the capybara. Right. They graze. Yeah, yeah, exactly.

So that's a good evidence of a functional relation between the toenails and being able to handle food. Are claws just longer nails or are they their own thing? They're not the same thing. So clothes and nails are basically made of keratin's, but they develop differently, at least as far as we know. And for example, even the bone underneath have a different structure to support either the claws or the nail. So, like, to be clear, a claw is not just a long nail. They are different, they have a different composition. Rafael, I'm going to ask you this.

Do you feel like thumbnails are kind of overlooked? I mean, they're this tiny appendage. I don't think we give them much thought. What's the bigger story about this? The thing is, for mammals in general and as evolutionary biologist, we tend to overlook some structures. We have some descriptions like species descriptions that mention the tongue, the presence of a tongue nail in rodents, but they always describe them as vestigial or redimentary. making the impression that they are like not functional. And that's one of the beautiful things about this study.

I can speak for myself that I was studying schools when we started this project and I never even thought about looking into nails. Do you look at your own thumbnails with more respect now? Yeah, with respect and with more love, maybe. I was so surprised when I saw the first pictures of rodent's hands and thumbnails, because they are short as our nails. And they really look like a nail. Like if you show a hand of a rodent, most people, they would not guess it was a rodent hand.

Oh my gosh, I know. The pictures, which we'll put on our website at sciencewriti.com slash thumbnail are pretty shocking. It's going to be like my iPhone background, you know? Yeah. And for me, before this project, I never fought on rodent's thumbnails. But now every time I see a squirrel, it's the first thing that comes to my mind. Like, oh, my God, that's amazing. I can only picture the thumbnail in my mind.

Thank you both so much for taking time to talk to me today. Yeah, thank you. Thank you for the interested in our study. Yeah, it was a pleasure to talk with you. Anderson Fejo is a mammal curator at the Field Museum in Chicago, and Rafael Missagia is an assistant. professor at the University of South Paulo in Brazil. Today's episode was produced by Charles Bergquist.

I'm Flora Lichtman. Thanks for listening.