“The sophistication that animals have evolved to treat wounds is unparalleled in the animal kingdom. The closest equivalent would be our human medical system,” Eric Frank, a behavioral ecologist at the University of Würzburg who led the study, said in an interview Wednesday. “These amputations prevented infection from spreading through the body. They had the same effect as amputations in medieval humans,” he said, adding that the findings are the first recorded instance of a non-human animal mutilating another of its own kind to save its own life.
the study, The study was published Tuesday in the journal Current Biologysuggests that Florida carpenter ants (Camponotus floridanus) can distinguish between different types of wounds and adjust their healing responses accordingly, improving our understanding of the sophisticated strategies that ants deploy to care for each other when injured, including triaging the wounded and treating those infected with microbial agents.
Scientists observed the amputations performed by Florida carpenter ants in a laboratory setting. Reddish, blackish, or brown ants Their body lengths are typically less than 1/2 inch. Unlike other ants, Florida carpenter ants lack the ability to secrete antibacterial secretions from glands to fight pathogens in wounds. “We wanted to see how a species that has lost these glands would care for an injured person,” Frank says.
The scientists began by deliberately injuring the femur (closer to the body) or tibia (further down the leg) of about 100 ants and comparing the reactions of fellow ants in the colony. They found that the ants effectively amputated when their nestmates injured their femur, but not when they suffered equivalent damage to the tibia.
In the former case, in more than three-quarters of cases, helpful nestmates performed surgical amputation of the injured insect’s entire leg.
Ali’s amputation surgery took about 40 minutes, and followed the same pattern each time: “Ali starts licking the wound with his mouth, then moves his mouth down the leg to the shoulder, where he begins biting pretty viciously for many minutes at a time,” Frank says. “The injured Ali calmly waits for the surgery to proceed, not complaining until his leg has been amputated.”
Among the ants whose femurs were injured, 95 percent who received amputations survived, compared with just 45 percent of those who didn’t, Frank said.
“The ants have found a strategy that, in their world, in their context, is highly efficient and leads to very high levels of success,” Frank concluded.
Laurent Keller, an evolutionary biologist who worked on the study, said the amputations were done very effectively. “What that means is that when you do an amputation, you have to do it in a very clean way so you don’t get any bacteria into the wound,” Keller said.
In contrast to the treatment received by the ants with injured femurs, the ants with injuries to the tibia (further down the leg) were never seen to undergo amputation surgery by their nestmates. “In these cases, the ants just cleaned the wound,” Keller said, adding that the nestmates instead provided extensive wound care, including licking the wound repeatedly.
Cleaning the wound also proved effective: About 70 to 75 percent of the ants whose fellow ants cleaned their wounds survived, whereas only 15 percent of the ants with injured tibias survived when they were left isolated from their fellow ants, Frank said.
Scientists offer one explanation for amputation decisions It has to do with how hemolymph, the fluid equivalent to blood, flows through the bodies of invertebrates.
Although this theory has yet to be tested, the scans showed that the tibia region of the leg has a greater hemolymph flow than the femur region, meaning that any pathogens that enter through the tibia would spread quickly to other parts of the body. This means that the window of opportunity for amputation to prevent the spread of infection is significantly shortened. “If the wound is at the tibia level, we don’t do amputation because normally the blood, and in insects the hemolymph, circulates very quickly, so within 40 minutes the blood carries the bacteria into the ant’s body,” Keller explained.
The painstaking efforts the ants make to tend to each other’s wounds show how social insects can benefit from altruistic behavior, Keller said. “By helping each other, they’re indirectly helping themselves.”
“Evolutionarily speaking, the colony saves a huge amount of energy by keeping injured ants alive and well, rather than simply discarding them and replacing them with new workers,” he says. Previous studies have shown that ants that have lost one or even two legs can still be productive members of the colony, regaining their normal running speed within a day and often performing the most dangerous tasks. He adds: “Even in ant societies, individuals have value.”