Ants perform limb amputations on injured comrades to save their lives

WASHINGTON — Limb amputations are performed by surgeons when a traumatic injury, such as a war wound or a car accident, 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 will 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 more than a half-inch long that lives 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 performs amputations on another individual to save its life,” said entomologist Erik Frank of the University of Würzburg in Germany, lead author of the study 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.

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.

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

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 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, which allows enough time for timely and effective amputations,” Frank said.

In both cases, the ants first clean the wound, probably applying secretions from glands in the mouth and probably also sucking out infected and dirty hemolymph. The amputation process itself takes at least 40 minutes and sometimes more than three hours, with constant biting of the shoulder.

For amputations following a thigh injury, the documented survival rate was approximately 90-95%, compared to approximately 40% for untreated injuries. For lower leg injuries where only cleaning was performed, the survival rate was approximately 75%, compared to approximately 15% 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, which have six legs, are fully functional after losing one. 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?

“This is an interesting question and it challenges our current definitions of empathy, at least to some extent. I don’t think the ants are what we would call ‘compassionate,'” Frank said.

“There’s a very simple evolutionary reason to care for the injured. It saves resources. If I can rehabilitate a worker with relatively little effort and then go on to be an active productive member of the colony, that’s very valuable. At the same time, if an individual is too badly injured, the ants won’t care for her, but will leave her to die,” Frank added.

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