Life is tough for Florida black ants. These half-inch ants are highly territorial and can get into fierce battles with ants from rival colonies in the Southeast.
Fighting can result in injuries to the ants' legs, but as scientists recently discovered, these ants have evolved an effective way to treat wounds: amputation.
Writing in the journal Current Biology on Tuesday, the researchers reported that the ants bite off the injured limbs of their nestmates to prevent infection. While other ant species are known to tend to wounds, usually by licking them clean, this is the first time an ant species has been found to use amputation to treat injuries.
The ants in this study only performed amputations in response to specific leg injuries, suggesting that their surgical procedures were planned. No other animal is known to perform such amputations outside of humans. The prevalence of this behavior in Florida carpenter ants raises questions about the ants' intelligence and ability to feel pain.
In early 2020, Danny Buffatto, a graduate student at the University of Lausanne in Switzerland, was observing a colony of Florida carpenter ants in his lab when he noticed something odd: “One ant was biting off the leg of another ant,” Buffatto says. At first, his supervisor didn't believe him.
“But when he showed me the video, I immediately knew we were on to something good,” says his supervisor Eric Frank, now at the University of Würzburg.
They began tracking the survival rates of the amputated ants, and unexpectedly, ants with amputated limbs survived 90 percent of the time.
Even more amazing, the amputation appears to be consensual: “The ant puts out its injured leg and sits there quietly while the other ants gnaw it off,” Dr. Frank says. “As soon as the leg falls off, the ant puts out the freshly amputated wound, and the other ants clean it up and finish the job.”
After observing dozens of amputations, the researchers realized that the ants only performed the procedure on nestmates who had suffered thigh injuries.
To understand why the ants only performed amputations on those with thigh injuries, the researchers also performed amputations on those with lower leg injuries, which had an amputation rate of just 20 percent.
“Amputation doesn't work if the wound is far from the body, but it works if it's close to the body,” Dr. Frank said.
It was counterintuitive, he says, but after Dr. Frank and his team carried out micro-CT scans of amputee patients, an explanation emerged.
Ants have several muscles throughout their bodies that keep fluids like blood flowing. Florida carpenter ants have many such muscles in their thighs. Injuring the thigh reduces the flow of fluids, making it harder for bacteria to get into the body through the wound. If the entire leg is quickly amputated in such a case, the chances of infection are very low.
But when Florida carpenter ants injure a leg, bacteria can quickly get into the body, making amputation procedures both quick and unlikely to succeed. And to some extent, the ants seem to be aware of this, says Dr. Frank.
“It's pretty crazy to think that something as simple as an ant 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 creatures but was not involved in the study, “but I wouldn't be surprised if other ant species exhibit similar behaviors.”
Dr. Kronauer said such amputations save lives and benefit the entire colony by limiting the spread of pathogens.
“Roughly 10 to 20 percent of hunting ants will become injured during their lifetime, and if colonies hadn't developed strategies to help these ants recover, they would need to produce 10 to 20 percent more ants to make up for this loss,” Dr. Frank said. “Rescuing injured ants saves a huge amount of energy at the colony level.”
Dr Frank, who has spent his career studying how ants heal wounds, said the new findings have changed his view of ants.
“This experience made me realise the value of every single ant in the colony and how beneficial it is to treat injured ants rather than let them die,” he said.
