In a frame taken from a video, an ant at the bottom of the frame bites the leg of an injured ant with a purple marker on its back.
Danny Buffat

The researchers observed Florida carpenter ants (Camponotus floridanus) biting the injured legs of their nest mates. By removing their mates’ legs, the ants significantly improved their chances of survival, researchers reported Tuesday in the journal Current Biology.

These surgeries are the first known example of nonhuman animals performing amputations to improve another animal’s chances of recovery, the authors say.

“Not only are they able to do that, but they’re even able to diagnose injuries and, depending on where they’re located, tailor treatment accordingly to maximize the chances of survival for those injured,” Erik Frank, first author of the new study and an ant researcher at the University of Würzburg in Germany, tells NPR’s Nell Greenfieldboyce. “I find that really remarkable.”

The discovery “pushes the boundaries of our understanding of behavioral immune systems in social insects,” says James Traniello, who studies insect social behavior at Boston University and was not involved in the study. New scientistThis is Chen Ly.

Some ant species secrete antimicrobial substances that they apply to wounds to fight pathogens. But Florida carpenter ants don’t have the glands that produce these secretions, even though they are territorial and can sustain injuries defending their habitat from rivals. So the researchers wondered if this species had other methods for treating infected wounds.

They found that when a worker ant injured its upper leg, the other ants in the nest would amputate it about three out of four times. These other ants would lick the wound and then spend an average of about six minutes biting the upper leg until it came off.

“I find it striking how freely they cooperate in this amputation case,” Frank says. National GeographicJason Bittel: “You can see her presenting her injured leg, and the other one (ant), for several minutes, is biting her ferociously… and the injured ant doesn’t seem to complain.”

Ants amputate the limbs of their nest mates to protect them from infection

But if the injury occurred in the lower part of the leg, other ants would usually not amputate it.

The researchers wondered whether amputations could help prevent infections. To test this hypothesis, they manually injured the legs of some ants. They isolated some of them, ensuring they would not receive any medical attention, performed their own amputations on others, and returned a third group to the colony. The team also infected some of the ants’ wounds.

Isolated ants with upper leg injuries died about 60 percent of the time, while ants operated on by researchers or other ants almost always survived, suggesting that medical care saved lives. But for ants with lower leg injuries, it doesn’t seem to matter whether they received medical care or not: both isolated ants and those that had their legs amputated by researchers died at high rates.

The experiments confirmed that ants did not perform amputations for lower leg injuries, and the researchers’ low success rate of amputations suggested that such methods would be ineffective anyway. But when ants with injured lower legs were in their colony, other ants licked the wounds, according to National GeographicInjured ants had a survival rate of about 75%, compared to about 15% for isolated ants with lower leg injuries.

Researchers speculate that amputation might be more effective for upper leg wounds because of the way they can affect blood flow.

Florida carpenter ants, like other insects, have muscles responsible for blood flow to their upper legs. Injuries to the upper legs could therefore reduce circulation. Reduced circulation would, in turn, reduce the spread of infection, giving the ants time to perform amputations and save their fellow ants. The researchers found that amputations for lower leg injuries only improved survival if they were performed immediately after the injury, supporting the idea that infections can spread quickly after lower leg injuries.

“It’s a very interesting finding,” says Corrie Moreau, an entomologist at Cornell University who was not involved in the findings. National Geographic“These researchers have not only shown that amputation increases survival, but they have also shown that isolated ants cannot bite off their own leg and are more likely to die.”

Ants “don’t just do a blanket amputation on any wound, they only do it when it makes sense,” says Tomer Czaczkes, who studies ant behavior at the University of Regensburg in Germany and was not involved in the study. New scientist.

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