The life of a Florida carpenter ant (Camponotus floridanus) can be brutal. These territorial ants engage in violent conflicts with rival colonies in the Southeast, often resulting in severe injuries. However, scientists have recently discovered a remarkable adaptation in response to these battle injuries: amputation.
In a new study out today, researchers report that Florida carpenter ants bite off the injured limbs of their nest mates to prevent infection. While other ant species are known to lick wounds clean, this is the first documented instance of amputation as a treatment.
Ants’ Surprising Surgical Skill
Dany Buffat, a graduate student at the University of Würzburg in Germany, first observed this behavior in 2020. He noticed one ant biting off another’s leg and shared a video of the event with his adviser, ecologist Erik Frank. The researchers then tracked the survival rates of the amputees, discovering that ants with amputated limbs survived 90% of the time.
“When we’re talking about amputation behavior, this is literally the only case in which a sophisticated and systematic amputation of an individual by another member of its species occurs in the animal Kingdom,” said Frank.
The amputations appear to be methodical and consensual. Injured ants present their legs to their nest mates, who first seem to perform a sort of first aid, cleaning the wounds with their mouthpieces. If the wound is severe, the ants bite off the injured limb.
The researchers found that amputations were only performed on ants with thigh injuries, which have a higher survival rate due to a lower flow of hemolymph (the equivalent of ant blood), which makes it more difficult for bacteria to infect the rest of the body from the wound.
“Femur injuries, where they always amputated the leg, had a success rate around 90% or 95%. And for the tibia, where they did not amputate, it still achieved about the survival rate of 75%,” says Frank.
In contrast, when the researchers performed amputations on ants with lower leg injuries, the survival rate dropped to 20%. With such types of injuries, bacteria are much better suited to infect the ant’s body, micro-CT scans revealed.
Remarkably, the ants seem to be aware of this fact, although it’s not clear how.
Speed seems crucial. An ant-assisted amputation requires around 40 minutes to complete. However, tibia injuries seem to be more deadly, causing ants to succumb faster.
“Thus, because they are unable to cut the leg sufficiently quickly to prevent the spread of harmful bacteria, ants try to limit the probability of lethal infection by spending more time cleaning the tibia wound,” said senior author and evolutionary biologist Laurent Keller of the University of Lausanne.
Implications for Ant Colonies and Evolution
This behavior highlights the ants’ sophisticated approach to colony survival. By performing amputations, they save energy that would otherwise be spent producing new ants. Furthermore, this strategy benefits the entire colony by reducing the spread of infections and conserving resources.
Although ant society is seen as cold and harsh, where any individual can be quickly discarded if the colony benefits, these findings show that some colonies recognize that caring rather than abandonment is sometimes better.
“The fact that the ants are able to diagnose a wound, see if it’s infected or sterile, and treat it accordingly over long periods of time by other individuals—the only medical system that can rival that would be the human one,” Frank says.
Since the remarkable medical behavior of these ants is innate, the researchers plan on running similar experiments with other members of the Camponotus genus and see whether amputation is common in other species.
“When you look at the videos where you have the ant presenting the injured leg and letting the other one bite off completely voluntarily, and then present the newly made wound so another one can finish the cleaning process—this level of innate cooperation to me is quite striking,” says Frank.
The findings were reported in the journal Current Biology.
