Ants can save each other’s limbs, new research shows

Surgeons amputate a limb when a traumatic injury causes extensive tissue destruction, or in cases of severe infection or disease. But humans aren’t the only ones who perform such procedures.

New research shows that some ants amputate limbs from injured comrades to increase their chances of survival. The behavior was documented in Florida carpenter ants — scientific name Camponotus floridanus —a reddish-brown species over 1.5 centimeters long found in parts of the southeastern United States.

These ants were observed treating injured limbs of nestmates, either by cleaning the wound with their mouthparts or by amputating by biting off the injured limb. The choice of treatment depended on the location of the injury. If it was further up the leg, they always amputated. If it was further down the leg, they never amputated.

“In this study, we describe for the first time how a non-human animal uses amputation 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 caring for the injured is the most advanced system in the animal kingdom, rivaled only by our own,” Frank added.

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

“If fighting breaks out, there is a risk of injury,” Frank said.

The researchers studied injuries to the upper part of the leg, the femur, and the lower part, the tibia. Such injuries are often found in wild ants of various species, sustained during fights, hunting or predation by other animals.

The ants were observed under laboratory conditions.

Different treatment options

“They’re deciding between amputating the leg or spending more time treating the wound,” Frank said. “How they decide, we don’t know. But we do know why the treatment is different.”

It has to do with the flow of hemolymph, the blue-green fluid that is similar to blood in most invertebrates.

“Injuries further up the leg have increased hemolymph flow, meaning pathogens can enter the body after just five minutes, rendering amputations useless by the time they can be performed. Injuries further down the leg have much slower hemolymph flow, allowing enough time for timely and effective amputations,” Frank said.

In both cases, the ants first cleaned the wound, probably by applying secretions from glands in the mouth and probably also sucking away infected and dirty hemolymph.

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

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High survival rate with amputation compared to no treatment

For amputations following a thigh injury, the documented survival rate was about 90 to 95 percent, compared to about 40 percent for untreated injuries. For lower leg injuries that were cleaned alone, the survival rate was about 75 percent, compared to about 15 percent for untreated injuries.

Wound care has been documented in other ant species that apply an antibiotic-effective glandular secretion to injured nestmates. This species lacks that gland.

Ants have six legs, but can still function fully after losing one.

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Saharan silver ants are the fastest recorded ants in the world, partly because of the way they run. Harald Wolf of the University of Ulm in Germany describes it as “galloping.”

It was female ants that showed this behavior.

“All worker ants are females. Males play only a small role in ant colonies — they mate once with the queen and then die,” Frank said.

Why do ants perform 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 who then goes on to be an active productive member of the colony, that’s a huge value.

“If an individual is too badly injured, the ants will not care for her, but leave her to die,” Frank adds.

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