The life of a Florida carpenter ant can be violent. These half-inch ants are territorial and have violent bouts with ants from rival colonies in the southeast.
Fighting can leave ants with leg injuries. But as scientists recently discovered, these ants have evolved an effective wound treatment: amputation.
In the journal Current Biology on Tuesday, the researchers report that 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 has been known to use mutilation to heal an injury.
The ants in the study only performed amputations on certain leg injuries, suggesting they are methodical in their surgical practices. Apart from man, no other animal is known to perform such mutilations. The prevalence of the behavior among Florida carpenter ants raises questions about their intelligence and ability to feel pain.
In early 2020, Dany Buffat, a graduate student at the University of Würzburg in Germany, was observing a colony of Florida carpenter ants in his lab when he noticed something strange. “An ant was biting another ant’s leg,” said Mr. Buffett, who is now a biologist at the University of Lausanne in Switzerland and an author of the study. His advisor in Würzburg did not believe him at first.
“But then he showed me a video and I knew right away we had something,” said the adviser, Erik Frank.
They began to monitor the survival rate of amputees. Surprisingly, ants with amputated limbs survived 90 percent of the time.
Even more surprising, the mutilations appeared consensual. “The ant presents its injured leg and sits there calmly while another ant gnaws at it,” Dr. Frank said. “Once the leg is dropped, the ant presents the newly mutilated wound and the other ant finishes the job by cleaning it up.”
After observing dozens of amputations, the researchers noticed that the ants would only perform the procedure on nestmates with thigh injuries.
To understand why the ants only performed amputations on those with injured thighs, the researchers performed amputations on ants with injured lower legs. The survival rate of experimental amputees was only 20 percent.
“When the wound is farther from the body, amputations don’t work, but when they’re closer to the body, they do,” Dr. Frank said.
That was counterintuitive, he said. But an explanation emerged when Dr. Frank and his team performed micro-CT scans on the amputees.
Ants have several muscles throughout their bodies that keep the hemolymph, their version of blood, flowing. Florida carpenter ants have many such muscles in their thighs. When they sustain an injury to the thigh, the flow of hemolymph is reduced, making it more difficult for bacteria to move from the wound to the body. In such cases, if the entire leg is amputated quickly, the chance of infection is very small.
But when a Florida carpenter ant injures its lower legs, bacteria can infiltrate its body very quickly. As a result, the time window for a successful amputation is narrow and the probability of success is small. Ants, on some level, seem to know this, 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 Rockefeller University in New York who studies ants and other highly social organisms, but not participated in the research. “But I wouldn’t be surprised if other species of ants had similar behavior.”
Such amputations benefit the entire colony by saving lives and limiting the spread of pathogens, Dr. Kronauer said.
“About 10 to 20 percent of ants that go hunting end up getting injured in their lifetime. “If 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 rescuing the injured, they save a huge amount of colony-wide energy.”
Dr Frank, who has spent his career studying how ants heal wounds, says the findings of his new study have changed the way he looks at insects.
“It made me appreciate the value of a single ant in a colony and how beneficial it is to take care of the injured instead of just leaving them dead,” he said.
