Carpenter ants are the only other animals known to amputate besides humans, researchers say

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People are not the only ones who can perform amputations to save lives.

A new study has found that carpenter ants in Florida bite off the injured limbs of nestmates, depending on the location of the wounds, to help their ants survive.

Research has shown that approximately 90% to 95% of ants that undergo amputation survive the amputation and are able to perform their duties in the nest perfectly well, despite the loss of a leg.

The research, published Tuesday in the journal Current Biology, builds on earlier findings published in 2023 by the same international team of scientists.

That research found that another ant species, called Matabele ants, or Megaponera analis, use their mouths to secrete antimicrobial compounds to cleanse injuries and prevent potential infection. The compounds are produced by what are known as metapleural glands.

Most ants have these glands. But over time, some species—including Camponotus floridanus, also known as carpenter ants—have lost them through evolution.

Most ant species without metapleural glands are arboreal, meaning they live in trees, said lead researcher Erik Frank, a behavioral ecologist at the University of Würzburg in the German state of Bavaria.

“We think that their arboreal lifestyle means they are less exposed to pathogens than underground colonies,” Frank said.

Frank and his colleagues had planned to continue studying Matabele ants in Ivory Coast when the pandemic hit. As a result, the team switched to studying the common carpenter ants that were available in the lab.

“I wanted to see how an ant species that can’t use antimicrobials to treat wounds would care for their injured people,” Frank said.

The researchers were unprepared for what they saw: a surgical procedure previously only performed on humans.

Florida reddish-brown carpenter ants, which grow to about 1.5 centimeters (about three-fifths of an inch) long, are found in rotting wood in the southeastern United States. They must defend their nests from rival ant colonies, which can lead to injury.

Study co-author Dany Buffat, a doctoral student at the University of Lausanne in Switzerland, was the first to observe how the ants cleaned the wounds and performed the amputations.

“The biggest surprise was clearly the fact that they are doing amputations in the first place,” Frank said. “I never expected this and when our (master’s student) Dany Buffat first described the behavior to me, I didn’t believe it. It wasn’t until he showed me the videos that I really realized what we had discovered.”

Bart Zijlstra

You see a carpenter ant cleaning the wound of another ant.

While the team was watching the ants in action, senior author of the study Dr. Laurent Keller, an evolutionary biologist at the University of Lausanne, noticed another surprise: The ants only performed amputations if the leg injuries were on the thigh or femur. After biting off the leg, the ants used their mouthparts to lick the wound clean, likely removing bacteria.

However, if the injury was on the lower leg or shin, the ants only licked the wound intensively, resulting in a 75% survival rate.

To understand why the ants were so specific and to reproduce the injuries in a lab setting, the researchers removed a single ant from the nest and worked with small colonies of 200 ants. They then used microscissors to make controlled cuts in the ant’s leg.

“We put the ant on ice for a few minutes beforehand to calm it down and make it easier to manipulate,” Frank said. “We gently removed one from the nest, put it on ice, and then cut off its leg. Once the ant woke up (after a few more minutes), we released it back into the colony to be with its nestmates.”

Of the ants with injuries to the femur or tibia that were not treated in isolation, less than 40% and 15% survived, respectively.

The team also performed CT scans of the ants to better look at the insects’ injuries
and how their bodies react. A multitude of muscles in the ants’ thighs ensure that a
blood-like fluid called hemolymph circulates. Although ants are not humanoid
Hearts have multiple heart pumps and muscles in their bodies that perform the same function.

Injuries to the thigh impede blood circulation, Frank says. In addition, blood flow is reduced, which makes it harder for bacteria to circulate from the wound through the body. Amputation can therefore prevent bacteria from spreading through the ant’s body.

Bart Zijlstra

An ant bites off the leg of another ant after it sustained an injury to its thigh.

Meanwhile, the ant’s lower leg lacks the muscles needed for blood circulation. But any wound there would quickly introduce bacteria into the body, and there would be no time for amputation.

“In tibial injuries, the flow of hemolymph was less obstructed, meaning that bacteria could enter the body more quickly. Whereas in femur injuries, the speed of blood circulation in the leg was slowed,” Frank said.

The researchers found that amputations using ants took about 40 minutes. This is why the insects apparently chose to amputate the femur, but not the tibia.

“Because they can’t cut the leg quickly enough to prevent the spread of harmful bacteria, ants try to limit the chance of a deadly infection by spending more time cleaning the shin wound,” Keller said.

Researchers are still trying to unravel the complexities behind this seemingly innate ant behavior.

“Workers must have learned over the course of evolution that amputation was an efficient way to avoid infection and that it increased colony productivity by increasing the number of workers that could contribute to colony tasks,” Keller said.

These amputations are seen as altruistic behavior because the ants have to spend time and energy helping others, Keller said.

“The fact that ants can diagnose a wound, see if it’s infected or sterile, and treat it accordingly with other individuals for a long time — the only medical system that can compete with that is the human system,” Frank said.

But Frank said he doesn’t think the ants consciously know what to do. Instead, it may be more instinctive, similar to how people put their fingers to their lips after a paper cut.

“We instinctively put our finger in our mouth and suck on it and don’t actively think about applying the antiseptic proteins in our saliva to the wound to prevent infection,” Frank said. “It’s probably similar for the ants. There was strong enough evolutionary pressure for them to have two different behaviors at two different types of wounds to maximize their (nest mates’) chances of survival. How they can tell them apart is a different question and one I’m currently working on.”

Now the researchers want to find more examples of wound care, not just in ants, but throughout the animal kingdom.

“We continue to study the wound-care behavior of other ant species and try to understand its evolutionary origins,” Frank said. “What did the ancestral wound-care behavior look like? Why do some amputate while others use antimicrobials?”

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