Life can be brutal for a Florida carpenter ant. These half-inch ants are territorial and have violent attacks with ants from rival colonies in the southeast.
Fighting can cause leg injuries to the ants. But as scientists recently discovered, these ants have developed an effective wound treatment: amputation.
In the journal Current Biology, researchers reported Tuesday that the ants bite off the injured limbs of their nestmates to prevent infection. While other ant species are known to tend to the wounds of their injured, usually by licking them clean, this is the first time an ant species is known to use amputation to treat an injury.
The ants in the study performed amputations on only certain leg injuries, suggesting that they are methodical in their surgical practices. No other animal besides humans is known to perform such amputations. The prevalence of the behavior among Florida carpenter ants raises questions about their intelligence and their ability to feel pain.
In early 2020, Dany Buffat, a doctoral student at the University of Würzburg in Germany, was observing a colony of Florida carpenter ants in his lab when he noticed something strange. “One ant was biting off the leg of another ant,” said Mr. Buffat, now a biologist at the University of Lausanne in Switzerland and one of the study’s authors. His advisor in Würzburg didn’t believe him at first.
“But then he showed me a video and I knew right away we were on the right track,” said consultant Erik Frank.
They began to track the survival rate of the amputees. Unexpectedly, the ants with amputated limbs survived 90 percent of the time.
Even more surprising is that the amputations were consensual. “The ant exposes its injured leg and sits quietly while another ant gnaws it off,” Dr. Frank said. “Once the leg falls off, the ant exposes the newly amputated wound and the other ant finishes the job by cleaning it.”
After observing dozens of amputations, the researchers noticed that the ants only performed the procedure on nestmates with injuries to their thighs.
To understand why the ants only performed amputations on ants with injured thighs, the researchers performed amputations on ants with injured lower legs. The survival rate of the subjects was only 20 percent.
“If the wound is farther away from the body, amputations don’t work, but if the wound is closer to the body, they do work,” Dr. Frank said.
That was counterintuitive, he said. But an explanation came after Dr. Frank and his team performed micro-CT scans on the amputees.
Ants have several muscles in their bodies that allow hemolymph, their version of blood, to flow. Florida carpenter ants have many such muscles in their thighs. When they sustain a thigh injury, the flow of hemolymph is reduced, making it harder for bacteria to enter the body from the wound. In such cases, the chance of infection is very low if the entire leg is amputated quickly.
But if a Florida carpenter ant injures its lower legs, bacteria can enter its body very quickly. As a result, the window for successful amputation is narrow and the chances of success are low. The ants seem to be aware of this on some level, says Dr. Frank.
“It’s pretty crazy to think that animals as simple as ants could have evolved such complex behavior,” said Daniel Kronauer, an associate professor at The Rockefeller University in New York who studies ants and other highly social organisms but was not involved in the study. “But I wouldn’t be surprised if other ant species exhibit similar behavior.”
According to Dr. Kronauer, such amputations benefit the entire colony because they save lives and prevent the spread of pathogens.
“About 10 to 20 percent of the ants that go hunting end up being injured in their lifetime. If the colonies had not developed strategies to help these ants recover, they would have to produce 10 to 20 percent more ants to compensate for this loss,” Dr. Frank said. “By saving the injured, they save a tremendous amount of energy at the colony level.”
Dr. Frank, who has spent his career researching how ants treat wounds, says the findings of his new study have changed the way he views insects.
“It made me realize how valuable an individual ant is to a colony and how useful it is to care for injured ants instead of leaving them to die,” he said.
