Laboratory experiments show that some ants treat the injured legs of their comrades and, if necessary, even perform medical amputations. Image: Bart Zijlstra, UNIL/

Ants Treat Some Leg Wounds With Life-Saving Amputations

When an ant injures its leg, it sometimes turns to a friend who helps it by gnawing it off, thus effecting a life-saving amputation of the limb.

This is what some new experiments described in the journal reveal Current Biologywhich show that ants are the only animal, other than humans, known to practice amputation as a medical treatment.

“Not only are they able to do this, but they are even able to diagnose injuries and, depending on their location, adapt treatment accordingly to maximize the chances of survival of the injured,” says Erik Frank, who studies “social wound care” in ants at the University of Würzburg in Germany. “I find that really remarkable.”

Wound Care After Battle

In the past, his group has studied how termite-hunting ants in the tropics dramatically reduce mortality rates among their injured mates by treating their wounds with antibiotic secretions from a special gland.

But this gland does not exist in a common species known as Florida carpenter ants, or Camponotus floridanusThis species nests in rotting wood and will fight rivals to defend its home, so Frank wanted to see how these ants would react when faced with the kind of injuries that come with battles.

His team quickly observed that these ants were cutting off injured legs, like miniature Civil War-era surgeons. “And that really piqued my curiosity,” he says.

An injured ant presents its leg to another ant, which licks the wound and then moves its leg up to bite the shoulder joint for several minutes, until the leg is severed. “You can see that the other ant doesn’t move, doesn’t really flinch, and accepts the situation,” Frank explains.

Almost all of the injured ants that had their legs amputated by a friend survived. In contrast, ants whose legs had been injured and who had been kept away from their peers to avoid this treatment often died.

To see how effective the amputations were, the researchers experimentally infected open wounds on ants’ legs with pathogens. They found that the type of amputations the ants performed prevented the infection from spreading and becoming fatal.

Frank went even further and surgically amputated the ants’ injured legs himself, mimicking the ants’ surgical approach, to see how the amputee fared. This confirmed, he says, that “these amputations were saving the lives of the infected people.”

The research has convinced other ant scientists who weren’t involved in the studies, such as Daniel Kronauer of Rockefeller University. “The experiments are very thorough,” Kronauer says. “To me, it seems plausible.”

“Here you have a species of ant that lives in a log in my backyard, where I grew up in Florida, and has been practicing clinical amputation for millions of years, probably longer than humans have ever done it,” says Clint Penick, a social insect researcher at Auburn University who was also not involved in the work.

“It’s really cool to see something like this, and to see really solid research that proves that this is actually a medical treatment that ants have evolved to do to prevent infection,” Penick says.

Armed with amputation instincts?

Interestingly, the ants only performed amputation when the wound was at the top of the ant’s leg, near the middle of its body. Wounds lower on the leg did not result in this treatment, although the ants did lick the wounds.

This observation prompted Frank’s team to try performing amputations on ants whose lower legs had been injured by bacteria. They found that the ants always died.

Frank and his colleagues wondered why amputation only seemed to work for upper leg injuries, until they looked closely at the anatomy of the leg. They found that the muscles in the upper leg normally help move a blood-like fluid through an ant’s body. These are the muscles that are damaged when an upper leg injury occurs. This means that bacteria or other pathogens present in an upper leg injury spread to the rest of the body more slowly than they would in a lower leg injury.

The fact that ants only perform amputations under certain circumstances is “really cool,” Kronauer says.

“They can determine where the injury occurred on the leg, right? And depending on exactly where the leg was injured, it makes sense or doesn’t make sense to amputate,” he notes.

He cautions, however, that it is not as if the ant doctors are assessing the wound and consciously weighing the pros and cons of treatment options, as a human doctor would.

“I don’t think they have extraordinary cognitive abilities,” Kronauer says. “They’ve evolved over thousands and thousands, if not millions, of years to be sort of ‘hardwired’ to respond in a certain way to different types of injuries.”

Yet, Penick says, humans tend to think of their medicine as particularly sophisticated, yet this common barnyard ant essentially does surgery.

And even when an ant had a wound on the lower part of its leg that couldn’t be treated by amputation, he notes, its nest mates still tended to the wound, apparently applying some kind of antimicrobial secretion that often proved lifesaving.

“My own work shows that many ants produce antimicrobials,” adds Penick, who says amputation “is just another example of things that are part of the public health repertoire that ants have to work with.”

Audio Transcription

ARI SHAPIRO, HOST:

Ants often have to defend their nests from invaders. And in the process, their legs can get injured. Now, scientists say some ants are treating those injuries using an old staple of combat medicine: amputation. NPR’s Nell Greenfieldboyce reports.

NELL GREENFIELDBOYCE, BYLINE: Clinical amputation is a human practice that’s been around for at least 30,000 years. It turns out that ants have been doing it even longer, according to a new scientific report published in the journal Current Biology.

ERIK FRANK: This is the first example of medical amputation in the animal kingdom that we describe here.

GREENFIELDBOYCE: Erik Frank studies ants at the University of Würzburg in Germany. In the past, he has studied how some tropical ants heal the wounds of their fellow ants by applying antibiotic secretions from a special gland. But he recently began studying Florida carpenter ants, which don’t have this gland, and he immediately noticed something surprising. Ants with a wound on the upper part of a leg would present that leg to another ant, who would gnaw on it at the shoulder. Frank says the injured ant endured the procedure stoically.

FRANK: Don’t move, don’t really flinch and accept it.

GREENFIELDBOYCE: Once the leg was severed and fell off, the injured ant waited patiently for further medical attention.

FRANK: The other one is going to come back and lick the little stump that’s left, and he’s going to keep presenting it. So he’s clearly cooperating and wants the same thing as the guy who’s treating him, which is to have that leg removed.

GREENFIELDBOYCE: And here’s why. Frank’s lab experiments show that without amputation, the infection in the open wound spreads and is almost always fatal. Interestingly, though, amputation is only life-saving when the wound is in the upper part of the leg. And the ants seem to know this, because when the wound is lower down, they don’t amputate. Instead, they spend more time licking and nursing the damaged area, probably treating it with antibiotic compounds. Frank says it’s really striking to him that ants aren’t just capable of amputations.

FRANK: But they are even able to diagnose injuries and, depending on the location, adapt treatment accordingly to maximize the chances of survival of the injured.

GREENFIELDBOYCE: Researchers who study ants and weren’t involved in this study were equally impressed, including Clint Penick of Auburn University.

CLINT PENICK: This is an ant that I grew up with in my backyard. So it’s really interesting to see such sophisticated behavior, you know, that’s literally happening in people’s backyards, in a regular carpenter ant.

GREENFIELDBOYCE: He says ants produce all sorts of antimicrobial compounds and have evolved a remarkable set of medical treatments, including therapeutic amputation.

Nell Greenfieldboyce, NPR News.

(EXCERPT FROM THEE SACRED SOULS SONG, “EASIER SAID THAN DONE”)