Surgeons perform limb amputations when a traumatic injury results in significant tissue destruction or in cases of serious infection or disease. But humans aren’t the only ones who resort to such procedures.

New research shows that some ants perform limb amputations on their injured mates to improve their chances of survival. This behavior has been observed in Florida carpenter ants — scientific name Camponotus floridanus — a reddish-brown species measuring more than 1.5 centimeters long and living in parts of the southeastern United States.

These ants were observed treating the injured limbs of their fellow ants, either by cleaning the wound with their mouthparts or amputating it by biting the damaged limb. The choice of treatment depended on the location of the injury. When it was higher on the leg, they always amputated. When it was lower, they never amputated.

“In this study, we describe for the first time how a nonhuman animal uses amputations on another individual to save its life,” said entomologist Erik Frank of the University of Würzburg in Germany, lead author of the research published Tuesday in the journal Current Biology.

“I am confident that we can safely say that the ants’ ‘medical system’ for treating the wounded is the most sophisticated in the animal kingdom, rivaled only by our own,” Frank added.

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This species nests in rotting wood and vigorously defends its home against rival ant colonies.

“If fights break out, there is a risk of injury,” Frank said.

The researchers studied injuries to the upper leg, the femur, and the lower leg, the tibia. These injuries are common among wild ants of various species, sustained during fighting, while hunting or due to predation by other animals.

The ants were observed under laboratory conditions.

Different treatment choices

“They decide whether to amputate the leg or spend more time caring for the injury,” Frank said. “We don’t know how they make that decision. But we do know why the treatment differs.”

It has to do with the flow of hemolymph, the blue-greenish fluid equivalent to blood in most invertebrates.

“Wounds lower on the leg have increased hemolymph flow, meaning pathogens are already entering the body after just five minutes, making amputations unnecessary by the time they could be performed. Wounds higher on the leg have much slower hemolymph flow, allowing plenty of time for quick and effective amputations,” Frank said.

In both cases, the ants first cleaned the wound, probably applying secretions from glands located in the mouth, while probably sucking out the infected and dirty hemolymph.

The amputation process itself takes at least 40 minutes and sometimes more than three hours, with constant biting to the shoulder.

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High survival rate with amputation compared to no treatment

In the case of amputations following upper leg injuries, the survival rate recorded was about 90 to 95%, compared with about 40% for untreated injuries. In the case of lower leg injuries where simple cleaning was performed, the survival rate was about 75%, compared with about 15% for untreated injuries.

Wound care has been observed in other ant species that apply a glandular secretion effective on antibiotics to injured ants. This species does not have this gland.

Ants, which have six legs, become fully functional again after losing one.

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It was female ants that were observed engaging in this behavior.

“All worker ants are female. Males play only a minor role in ant colonies: they mate once with the queen and then die,” Frank explains.

So why do ants make these amputations?

“There’s a very simple evolutionary reason to care for the injured. It saves resources,” Frank said. “If I can rehabilitate a worker with relatively little effort and then they’re going to be a productive, active member of the colony again, that’s very valuable.”

“At the same time, if an individual is too badly injured, the ants will not take care of it, but will instead let it die,” Frank adds.