There are an astonishing number of ant species living on our planet. One of the world's foremost experts on ants, Dr. Susanne Foitzik, explains how their society is different from ours yet staggeringly complex nonetheless.

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ERIC: From the Museum of Science in Boston, this is Pulsar, a podcast where we go to the experts for answers to the most frequent questions we get from our visitors. I'm your host, Eric, and many of our visitors are fascinated with ants. They can be found on nearly every bit of land on our planet, they outnumber humans on Earth at least a million to one, and observing their behavior for even a few minutes reveals the fascinating complexities of their society. Our museum visitors love watching our colony of leaf cutter ants scurrying around, and they sometimes ask: how smart are ants? For the answer, I turned to Dr. Susanne Foitzik, one of the world's foremost experts on ants and their behavior. She's an evolutionary biologist at Johannes Gutenberg University in Mainz, Germany, and the author of Empire of Ants: The Hidden Worlds and Extraordinary Lives of Earth's Tiny Conquerors. Dr. Foitzik, thank you so much for joining me on the podcast all the way from Germany.

SUSANNE: You're welcome.

ERIC: So to start out with a really great, but simple question we got is: how smart are ants?

SUSANNE: Ah, that's a good question. I think compared to us, they are less smart. Nevertheless, them managed to have very well organized societies. They managed to come to a consensus agreement among many of the colony and sometimes show kind of swarm intelligence. Individual intelligence, let's say, add up. They can learn, they can remember, they can forget, they sometimes show individual personalities. So they're not little kind of robots who always do the same thing, by far not. But yeah, compared to us, I would say they're not as smart.

ERIC: One of the terms is drones, and we sort of everyday use, we think of drone as something that's automated or not as smart. But they they really are. Like you talked about in your book, the social behavior. What does that really mean for ants? You specialize in social behavior, can you talk a little bit about how ants have that social behavior that makes them kind of different than our society.

SUSANNE: Well ant colonies, basically, are a family group, with the mother, the queen being in a way the head, even though she doesn't organize it. It's very self organized. And normally, workers concentrate for part of their life on a certain job. They normally start out doing brood care. Ant babies, let's say, they are larvae. So a little bit like a caterpillar from a butterfly, you have a larval stage, you have a pupa stage. And then you have the adult stage, which we kind of connect to being an ant. But an ant baby looks like a little white worm, if you wish, and it needs all the care. So it needs somebody who defends it, somebody who cleans it, somebody who feeds it. And this is done by the young workers. And as the workers become older, they engage more in caring for adult workers and the queen. And then they do nest construction, they defend the nest. And finally, the oldest workers go out and search for new food and bring it back to the nest. And they do it so late in life because it's the most risky task. So it's good to send the old women out. And I say women because all the workers in ant colonies are female. And males are only produced once in the year and they fly out to mate with young queens and then they die. They live only a few days.

ERIC: So there's all these different jobs, all these different specialties, but nobody in charge. No one assigning jobs. It at all just happens?

SUSANNE: Yes, indeed. And that's actually fascinating. So our idea is that individuals differ in the likelihood to take over certain tasks. So imagine you live in a shared apartment with some buddies. And you'll often first notice that some are more likely to I don't know cook a dinner, and others are more likely to take out the trash. Uf you are lucky, everybody has a high likelihood to do some job and that they are not the total lazy ones who do nothing. Even though there are in the ant nest. There are papers on why are ants so lazy. So the ants we see are often the ants which run out and forage for food. And as I said, this is very risky. So they are normally very fast on their way and try to find the food. In the nest we actually see some individuals which are young, so individuals differ in the likelihood to pick up a job. Our research actually could show that they differ in the likelihood to smell certain odors, and ants have a chemical society. So they communicate not in oral language which we do, but they communicate with chemical signals. And we know that young workers over-express certain odor receptors, are they sensible to certain odors, and others to other odors. And when you don't perceive kind of a certain task, I mean, if somebody smells the garbage, and is kind of annoyed by it, he or she is more likely to bring it outside, then people who might not have such a sensible nose, and this seems to explain part of the variation we see. And if a task is not undertaken, so if nobody is there who cares for the larvae, the larvae will call out, I mean, not acoustically, but chemically: "is nobody there who cares for me here?" And then even workers who have normally very low likelihood to take over the task will then eventually do it, because everybody can do everything. Except that it is apparently more efficient if you, at least for part of your life, you concentrate on doing one task, you learn to become better, you gain experience, and you don't have to kind of switch tasks, which often takes a while, we know that if you do one job, I don't know. cooking, and then we have to do the washing, it often takes a while to kind of readjust. Okay, now washing. So what do I have to do, I have to separate different colors, okay, and you get this thing. And that's why you have this specialization. But it's not like human societies where you have one job all your life, you get one training and normally do this. But it's more that you kind of switch jobs during your lifetime.

ERIC: So you mentioned that some of that communication, it's not necessarily yelling out the way we would hear it. So ants communicate completely differently. Can you talk about how they use chemicals as signals to basically say anything?

SUSANNE: Maybe not anything. I think humans are unique in a way that we have this complexity of our language, which allows us to put down stories of what happened in the long past. And you can also give this information to the next, the next, the next generation by writing it down. But the ants communicate by two things. For one thing, they have chemicals on the cuticle of their skin, if you wish. They are hydrocarbons, long-chain fatty acids in the end. And this is a complex mixture up to 70 different substances they can have. Often it's only about 30 or so. And it's more like the shirt you wear when you play a certain, I don't know, soccer or American football, it always has a certain color. So it tells you this ant belongs to this colony. Each member of the colony kind of has a similar composition of these chemicals on the cuticle and the ants smell this with their antenna and they smell it and are like "oh, you belong to us, you have the same signal" if you wish. It's not only that they have like this one color, which tells you you belong to this family. But there might also be some colors, let's say the Queen has elements which show that she's a queen, that she's very fertile. And foragers might have slightly different ones. Because when they go out, they have to also protect the body for dehydration. So that might also change slightly. But lo and behold, you can really say, you belong to one colony and you belong to different colony. The second thing they are using is secretion from glands. So we found over 70 different glands, production sites, for certain chemicals which can be released to the outside. Glandular secretions are used to lay a trail. So you'll often see ants maybe outside walking all on the same paths. And this is because one ant found food there, she went back and laid the chemical trail. And then the other ants followed that trail, found also more food, and on the way back kind of strengthened that trail, and many ants can communicate the location of food or a new nest site by using this.

ERIC: It's amazing that ants have evolved this way to communicate just using these chemicals and smell. We have so many analogies: it's like a message board, it's like signposts, it's like an alarm. All of that is just done by laying down chemicals in different combinations.

SUSANNE: And it's also interesting because when you, for example, find a food source and you lay your trail back, this trail should only be maintained as long as there is food at the end of the trail. Once the food has been all harvested and there is nothing left, the trail should evaporate. And actually they can use different types of trails. Some trails which are more permanent than others to modulate this: okay, maybe this is a permanent food source, or a permanent way to get water because there is a little pond. So I mean maybe this trail it can be kind of maintained with a signal which doesn't evaporate whereas the other trails are more ephemeral food sources which go away, which are harvested, and they will evaporate because otherwise the ants will come out of the nest and like, "oh, there's food in there." They go there, and there is no food. And that actually is a waste of time and energy. And so they don't do that.

ERIC: So it's not just like painting a circle on a tree, it's something that will last only a certain amount of time unless it's replenished. It's amazing. So in your book, you talk a lot about the fieldwork that you've done. And there's so many great stories, I leave most of them to our listeners to go and read. But one of my favorites has to do with collecting ants and bringing them back to the lab. Can you talk about the challenges of doing that?

SUSANNE: Yeah, I mean, if you want to do more detailed observation of our ants, we like to have them in the lab, because then we can observe them, and the microscopes, or we can extract DNA, to look at kind of which genes are active. So I'm actually often working on ants which are tiny. The entire colony fits in an acorn or in a hickory nut. So basically, what we do, we sit on a forest floor opening acorns. And we did so in, I don't know, two years ago, we were in Massachusetts, and we are in New York and Maine. We sit on the forest ground, you open these acorns, and if we find an entire colony residing in one of those acorns, we then actually take the entire colony and put it in a Ziploc bag and put some leaves with it, and a little bit of wet tissue. And then normally, when we collect at different sites, you often can cool the ants down in the cooler. Because insects, when you cool them down, they kind of go to sleep. And that's the easiest way to transport them. Then we put them in our luggage and transport them to Germany.

ERIC: Do you get weird questions about that?

SUSANNE: Funny experiences. Sometimes you use an apparatus, which is called an aspirator. It's like a little vial with two hollow tubes coming out and basically suck on the one hand, and then the ant is kind of drawn into the little vial. There is a net so that you don't swallow the ant, you don't want that. So one time we actually collect them, we send them back to Germany. And then we were traveling somewhere else in the US. And I think in LA at the airport, they stopped us and found that device. And so we said well, it's for ant hunting. And the customs, they were not so convinced.

ERIC: Without the ants to prove it, it must be a little bit...

SUSANNE: I'm sure they thought it was a kind of a device where you can inhale up some kind of drugs with it. And that actually one of my colleagues luckily had one ant in alcohol in an Eppendorf vial, and he pulled that out and showed it to customs. And they're like, okay, maybe this story does make sense. Yeah, it's always fun. I really like fieldwork. It's really great.

ERIC: So what kind of fieldwork do you have coming up next? Is there anything exciting?

SUSANNE: Well, we will collect ants in upstate New York. We're going to look at division of labor. So what we just said, workers concentrated on brood care and others on foraging. So we found a few genes which are especially active as an ant does brood care. We want to understand whether this gene is also regulating the activity of the odorant receptors. As I said, this being sensitive to certain odors can regulate division of labor. And this is our new hypothesis based on data record from last year. And now we want to kind of test it, knock this gene out, to make it inactive, which you can experimentally do, and then see whether indeed, the odorant receptors are differently active in the antennae.

ERIC: To wrap up, why do you think it's important to study and understand ants? Why do you study ants?

SUSANNE: My answer would be because it's fascinating to see how you find the evolution of super complex societies which are so different, and nevertheless have a lot of traits which are so similar to human societies. I think it's just very fascinating to study them. So I do it mostly because of curiosity. Ants are important in ecosystems. I mean, because they're everywhere. They're at high densities. By building nests they fertilize the soil. This is an important trait. But as I said, I just love them because they are so fascinating.

ERIC: All right. Well, thank you so much for joining me and talking all about ants.

SUSANNE: You're welcome.

ERIC: You can find Empire of Ants: The Hidden Worlds and Extraordinary Lives of Earth's Tiny Conquerors at your local bookshop. On your next visit to the Museum of Science, Boston, head up to our Garden Walk and Insect Zoo to see our leaf cutter ant colony. And while you're at home, check out the colony's live stream at mos.org. Until next time, keep asking questions.

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