Like humans, these ants can perform leg amputations to save lives
EMILY KWONG: You're listening to Short Wave from NPR. Hey, Short Wavers, Emily Kwong here. We humans, we have incredibly sophisticated kinds of medical care. Other animals, not so much. Like, researchers, have seen evidence that some sick animals will self-medicate by eating clay or certain plants. But there is one creature in the animal kingdom who takes the practice of medicine-- air quotes, "medicine"-- to a whole different level. And that, my friends, is the tiny ant.
NELL GREENFIELDBOYCE: Which really should not surprise us. I mean, ants are amazing. I mean, some ants farm. [CHUCKLES] They farm fungi for their food. They herd aphids. I mean, if they've got agriculture, why not medicine?
KWONG: That is NPR's number one ant enthusiast and science correspondent, Nell Greenfieldboyce.
GREENFIELDBOYCE: Hey there.
KWONG: Nell, we wanted to have you on the show because you recently reported on one aspect of ant medical care that is truly mind-blowing, at least for me, even if you're not surprised about it.
GREENFIELDBOYCE: That's right. I was kind of surprised about this, actually, despite my admiration for ants' many abilities. So there's this new research out showing that ants will treat certain injuries with therapeutic amputation.
KWONG: Amputation. Just for comparison, how long have humans used amputation as a medical treatment?
GREENFIELDBOYCE: So if you look at evidence, like in the archaeological record, you can find ancient human skeletons with clear amputations that go back, like, over 30,000 years, so a long time. But the ants have probably been doing it for longer, much longer than us. And these aren't super rare ants or anything. These are common carpenter ants you can find in people's backyards in places like Florida.
KWONG: So in someone's backyard right now, a tiny ant surgeon is effectively practicing Civil War-era medicine, a.k.a. amputation.
GREENFIELDBOYCE: Yeah, and I mean, the Civil War medicine thing is a pretty good analogy because ants engage in battles and warfare. I mean, they hunt. They defend their territory. And that means when ants come home, back to the nest, they can be injured. And it turns out their nest mates take care of their wounded warriors. I mean, lab experiments show that their medical efforts-- including, now we know, amputations-- are very often life saving. And it turns out the ants are selective about when they perform amputations. They're not just like hacking off injured legs willy-nilly.
KWONG: All right, well, today on the show, we dive into the anthill to check out their health care system-- how scientists discovered that ants will perform medical acts that include clinical amputations, and how the ants determine whether or not an injured limb has got to go. You're listening to Short Wave, the science podcast from NPR.
KWONG: OK, now, so how did scientists learn that ants will sometimes treat an injury with amputation?
GREENFIELDBOYCE: So the lead researcher who did this work is named Erik Frank, and he's now at the University of Wurzburg in Germany. And he's really a tropical biologist. So years ago, he was studying some ants in Africa that will hunt and eat termites. And I talked to him back then, and he told me that ant scouts would go out and find a termite nest, and then hundreds of ants would march out together, like an army in formation--
ERIK FRANK: Like three ants next to each other in a 2-meter long column. It's very peculiar, and it looks like a long snake walking on the ground.
GREENFIELDBOYCE: So when the ants get to the termites, they would fight. There's this huge battle. And when it was over, he would see the ants start picking up dead termites to carry home for food. But then he noticed that some of the ants that were marching home weren't carrying termites. They were carrying other ants, wounded ants.
KWONG: So they were carrying their fallen comrades home.
GREENFIELDBOYCE: Yeah, basically, just like soldiers.
KWONG: Instead of no man left behind, no ants left behind.
GREENFIELDBOYCE: Exactly. And so he was really surprised by this. And he did a study where he marked the injured ants to see what happened to them. And it turns out, in nearly every case, the injured ants that were carried home made a full recovery.
FRANK: We saw them again participating in hunts the next day.
KWONG: What a rebound.
GREENFIELDBOYCE: Yeah, so he got interested in how they recovered. And by studying this, he learned that ants will lick and groom a buddy's wound in the hours after the injury. And without this treatment, the injured ants would usually die. So it turns out, this particular species of ant has a special gland that's full of antimicrobial secretions. And worker ants basically apply these secretions to the open wounds of their nestmates. It's basically like giving their injuries antibiotics.
KWONG: But are these the ants that engage in medical amputation?
GREENFIELDBOYCE: No. OK, so that's something Erik Frank only observed more recently. And when I talked to him, he told me it was because of the pandemic, because he couldn't travel. So he started studying this other ant. The common name is the Florida carpenter ant.
KWONG: I feel like so many scientists had to make do during the pandemic. People learned cool stuff just by studying what was around, which in his case was the Florida carpenter ant.
GREENFIELDBOYCE: It's true. I wish somebody would put a compilation of pandemic desperation science, where scientists looked around and saw what was there. Anyway, so he's now looking at this other ant, and he knew that this species did not have that special gland that he'd been studying before.
FRANK: So I just very naively wondered, well, how would they act if they get confronted with injuries?
GREENFIELDBOYCE: So these are, you know, injuries that they did experimentally in a controlled way in the lab. And pretty much right away, he and his colleagues saw ants amputating their buddy's injured legs.
KWONG: This has been my big question this whole time. When you say amputating, how does that work? Ants don't have tiny little bone saws and surgical tools.
GREENFIELDBOYCE: No, they don't. So here's what happens. An injured ant-- you know, an ant with an injury and like the upper part of its leg will present that leg to a nestmate. And this nestmate will lick at the wound with their little mouthparts, move up to the shoulder area, and up at the joint, start chewing through the leg to sever it.
KWONG: [GASP]
GREENFIELDBOYCE: And this takes a while, like many minutes.
FRANK: And you can see the other one not moving, not really flinching, and accepting it. And once the leg is removed and it falls off, the other one will come back and lick the little stump that's left, and they will still be presenting it. So it's clearly collaborating and wants the same thing as the one that is treating it.
GREENFIELDBOYCE: So either the injured ants are just stoic, or they don't feel pain or what, but they're clearly working together to make this thing happen.
KWONG: The depth of ants-- I just didn't realize any of this. And you said earlier that this procedure, for lack of a better term, is life-saving. How do researchers know that?
GREENFIELDBOYCE: So they found that ants with similar injuries that were kept away from their nestmates-- they didn't get amputations-- those ants frequently died. So no amputation, high chance of dying. And their studies show that's because, without amputation, an infection from an open leg wound can travel to the rest of the ant's body and kill it. And Erik Frank told me, to see if it was really amputation that was the key thing, he figured he'd just try his hand at performing ant surgery.
FRANK: Since I observed these amputations, I was like, well, I'm pretty sure I can artificially conduct the same kind of amputations.
GREENFIELDBOYCE: And so even when it was done by a human, the amputation treatment was just as effective in helping injured ants recover.
FRANK: Really confirming that these amputations were saving the lives of the infected individuals.
GREENFIELDBOYCE: Pretty cool, right.
KWONG: It's so cool. But wasn't there supposed to be some clinical judgment involved here? You alluded to earlier that ants aren't just whipping off legs right and left. They are making decisions about what to amputate.
GREENFIELDBOYCE: Well, decisions, I mean, that's a debatable word. But yeah, there is a part of this that the researchers found perplexing for a while. They had been studying ants with injuries to the upper leg and witnessing amputations at the shoulder. And so after they'd done this for a while, they were like, OK, what if an ant had an injury farther down, like towards its little ant foot. So it turns out that for injuries lower down, like what would be the human shin, the ants did not amputate legs at all. So amputation was only occurring when the injury was high up in, like, what would be a human thigh. It was like, what? That doesn't make sense. And it took Erik Frank and his colleagues, like, a year of lab work to figure out what was going on. And, basically, the important thing is that the body of an ant is just not like the human body.
KWONG: How so?
GREENFIELDBOYCE: Well, they don't have hearts like we do, for one thing. There are these muscular pumps distributed throughout the ant's body, including in its legs, especially in the thigh, the upper leg area. So it's weird, but what it means is that if an ant gets injured in that upper leg area, the muscles are damaged, and so the pumping of liquid doesn't happen as quickly. And that means infection actually spreads slowly, more slowly than it would if the injury was lower down on the leg. And so, basically, what it means is that amputation really only has a shot at blocking the infection for upper leg injuries, even though it doesn't seem like it should be that way. But that's how it is for ants.
KWONG: Right, and then if the infection is lower down on the leg, the infection spreads fast, the amputation can't work, and it's deemed a little bit of a lost cause?
GREENFIELDBOYCE: Yeah, so the researchers tested all of this experimentally in the lab, and they showed experimentally that amputation is not effective for lower leg injuries. And so that's why the ants don't do it.
KWONG: They are like doctors. They're like surgeons.
GREENFIELDBOYCE: So for those injuries, they just spend a lot of time tending to the wounds, licking them. And whatever they do is often life-saving.
KWONG: It's amazing to me that this treatment is so targeted to a specific kind of injury. They are making what we would call a clinical evaluation.
GREENFIELDBOYCE: Yeah, but they're not exactly like doctors. It's not like they're sitting there thinking about it and weighing the pros and cons. I talked about this with some other ant experts who weren't involved in this study, like Daniel Kronauer. He's at Rockefeller University. And he told me, remember, this is evolution working, not individual ants with medical degrees and medical knowledge.
DANIEL KRONAUER: They have basically evolved over thousands and thousands and probably millions of years to be kind of "programmed," in quotation marks, to react to different kinds of injuries in a certain way.
GREENFIELDBOYCE: It's all to help the colony as a whole survive. And he told me, besides these antimicrobial secretions and amputations, ants sometimes do other things that seem a lot like human public health measures. So, for example, there's studies showing that if ants in a nest have certain contagious infections, the social networks of the nest will get reconfigured. There's less connections. Everything becomes much more modular.
KWONG: So they'll quarantine, essentially.
GREENFIELDBOYCE: Yeah.
KRONAUER: You basically socially isolate individuals that carry the infection. That, of course, reminds you of the COVID pandemic maybe, and what we were supposed to be doing.
GREENFIELDBOYCE: And then there's other studies showing that ants with an infectious disease might just wander off from the colony and go die somewhere else.
KWONG: That's very self-sacrificing of that ant. And, again, the amputation and antibiotic parts, it all sounds very caring.
GREENFIELDBOYCE: Yeah, but it's not like it's love. It's not like empathy or anything. It's just that saving ant lives means that the colony has bigger armies and more success, just generally speaking. That's like one more soldier for your cause.
KWONG: OK, I'm hearing you. This is evolution at work. These are adaptive strategies for the good of the colony-- self-isolation, amputation, wound-licking. It's all very cool. And I guess what's striking to me is, given how useful it is, how have we not noticed this before? I mean, we've been living alongside carpenter ants for a long time.
GREENFIELDBOYCE: Yeah, I'm sure people listening to this have seen these ants before. I mean, they're not like the little black ants that invade your picnics. But the Florida carpenter ant is this brownish ant, like a centimeter across. It's in lots of places where people live. And that is the part that really struck this other guy I talked to, an ant expert called Clint Penick. He's at Auburn University.
CLINT PENICK: This is an ant that I grew up with in my backyard. And so it's really interesting to see such a sophisticated behavior that's literally happening in people's backyards from a common carpenter ant.
GREENFIELDBOYCE: It makes me wonder what else the ants are doing.
[LAUGHTER]
KWONG: Insects in general feel like the final frontier to me. There's so much we don't know about what they do. And I hope when you find something else, you come on the show and talk about it, Nell.
GREENFIELDBOYCE: Absolutely. I mean, I do admire your seemingly endless desire to hear this stuff. And if I know ants, pretty soon, we're going to be hearing about something else. There's going to be another supposedly unique-to-human activity that it turns out, oh yeah, ants have been doing for millions of years.
KWONG: Yeah, I mean what would be really weird is if they had their own science podcast.
GREENFIELDBOYCE: I mean, it would be serious competition for you, I got to say, because I would listen to that all day long. All day long, Emily.
KWONG: I would love to cohost with an ant. This episode was produced by Hannah Chinn. It was edited by our showrunner, Rebecca Ramirez, and fact-checked by Nell Greenfieldboyce. Beth Donovan is our senior director, and Collin Campbell is our senior vice president of podcasting strategy. I'm Emily Kwong. Thank you for listening to Short Wave, the science podcast from NPR.
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