Florida Carpenter Ants Perform Wound Cleaning, Amputations to Help Injured Nestmates

From their name, you might think Florida carpenter ants (Camponotus floridanus) are good at building things — and they are — but they have another potentially lifesaving talent: They are experts at wound care and surgery.

A common species native to the state, these amazing insects selectively treat their nestmates’ wounded limbs by cleaning or amputating them, a press release from Cell Press said.

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In a new study, an international team of researchers detailed how these “treatments” not only aided in nestmates’ recovery, but showed that the choice of care provided by the treating ants catered to the specific type of injury.

“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 Erik Frank, lead author of the study and a behavioral ecologist with the University of Würzburg, in the press release.

While wound care is not entirely novel among ants, carpenter ants are the only known species to use solely mechanical methods to carry out their treatments. A paper published last year found that another group of ants used a special gland to introduce antimicrobial compounds into injuries.

The research team discovered that carpenter ants’ mechanical care comes in two types: using their mouthparts to clean the wound and cleaning the wound prior to a full leg amputation. Before deciding which treatment to use, the provider ants seem to assess the injury in order to make educated adjustments regarding the best method of care.

The study analyzed two types of injuries: femur lacerations and lacerations on the ankle-like tibia. Initial cleaning was given for all femur injuries, followed by the removal of the leg by a nestmate chewing it off. The only treatment given for tibia injuries, however, was mouth cleaning.

In both cases, intervention led to a much higher survival rate for ants with infected wounds.

“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%,” Frank said in the press release.

Untreated infected tibia and femur abrasions had a survival rate of 15 and 40 percent, respectively.

The team surmised that the chosen type of wound care could be associated with infection risk from the wound site. Femur scans showed it is primarily made up of muscle tissue, which suggests it has a role in pumping blood from the leg to the main part of the body.

With femur injuries, the compromised muscles were less able to circulate blood that is potentially contaminated with bacteria. The tibia, on the other hand, doesn’t have much muscle tissue or involvement in the circulation of blood.

“In tibia injuries, the flow of the hemolymph was less impeded, meaning bacteria could enter the body faster. While in femur injuries the speed of the blood circulation in the leg was slowed down,” Frank said.

This would seem to mean that amputating the leg would be the best choice with tibia injuries, but the researchers found the opposite to be true. They discovered that how fast the ants were able to amputate made a difference.

It took a minimum of 40 minutes for an ant-assisted amputation. In cases of an injury to the tibia, it was shown that not amputating the leg immediately post-infection meant the ant would die.

“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 Laurent Keller, senior author of the study and an evolutionary biologist at the University of Lausanne, in the press release.

The study, “Wound-dependent leg amputations to combat infections in an ant society,” was published in the journal Current Biology.

“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 said.

Keller noted that these sophisticated behaviors seemed to be inherent in carpenter ants.

“It’s really all innate behavior,” Keller said. “Ant behaviors change based on the age of an individual, but there is very little evidence of any learning.”

The research team is currently conducting similar experiments in other species of carpenter ant to find out how intact the behavior is and whether all ant species that don’t have the antimicrobial gland perform amputations. The slow removal of an ant’s limb while conscious also brings up the consideration of pain in ant societies.

“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,” Frank said.