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

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Humans are not the only ones capable of performing amputations to save lives.

Florida carpenter ants have been observed biting the injured limbs of their nest mates, depending on the location of the injuries, to help their counterparts survive, according to a new study.

According to the researchers, about 90 to 95 percent of amputated ants survive the operation and continue to go about their tasks within the nest without problems despite the loss of a leg.

The study, published Tuesday in the journal Current Biology, builds on previous results published in 2023 by the same international team of scientists.

This research discovered that another species of ant, the Matabele ant, or Megaponera analis, uses its mouth to secrete antimicrobial compounds to clean wounds and prevent potential infections. The compounds are produced by what are called 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 that lack metapleural glands are arboreal, meaning they live in trees, said the study’s lead author, Erik Frank, a behavioral ecologist at the University of Würzburg in the German state of Bavaria.

“We think their arboreal lifestyle might expose them to fewer pathogens than colonies living underground,” Frank said.

Frank and his colleagues had planned to continue studying Matabele ants in Ivory Coast when the pandemic hit, so the team decided to study the common carpenter ants available in their lab.

“I wanted to see how an ant species that can’t use antimicrobial compounds to treat wounds would care for its wounded,” Frank said.

The researchers were not prepared for what they observed: a type of surgical procedure previously seen only in humans.

Florida carpenter ants, which are reddish-brown in color, are about 1.5 cm long and nest in decaying wood throughout the southeastern United States. They must defend their nests from rival ant colonies, which can result in injury.

Dany Buffat, a co-author of the study and a graduate student at the University of Lausanne in Switzerland, first observed the ants performing the wound cleaning and amputation measures.

“The biggest surprise was that they were performing amputations,” Frank said. “I didn’t expect that, and in fact, 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 understood what we had discovered.”

As the team watched the ants in action, Dr. Laurent Keller, lead author of the study and an evolutionary biologist at the University of Lausanne, noticed another surprise: The ants only amputated if the leg injuries occurred on the thigh or femur. After biting the leg, the ants used their mouthparts to lick the wound, likely removing bacteria.

But if the wound was located on the lower leg or shin, the ants simply licked the wound intensively, giving a 75% survival rate.

To understand why the ants were so specific in their care and to recreate the injuries in the lab, the researchers removed a single ant from the nest, working with small colonies of 200 ants, and used microscissors to make controlled cuts on the ant’s leg.

“We would first put the ant on ice for a few minutes so it would calm down and be easier to handle,” Frank explains. “We would carefully remove it from the nest, put it on ice, and then cut off the leg. Once the ant woke up (after a few minutes), it would be released back into the colony to join its nest mates.”

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

The team also performed CT scans of the ants to take a closer 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 do not have a structure similar to that of humans
hearts, they have several heart pumps and muscles throughout their body that perform the same function.

Thigh injuries impede that circulation, Frank said, and because blood flow is reduced, bacteria can’t travel from the wound and through the body as quickly, meaning an amputation can prevent the bacteria from spreading throughout the ant’s body.

In contrast, the lower part of the ants’ leg contains no muscles needed for blood circulation. But any injury there would quickly introduce bacteria into the body, and there would be no time for amputation.

“In the case of tibia injuries, the circulation of hemolymph was less impeded, which allowed bacteria to enter the body more quickly. In the case of femur injuries, the speed of blood circulation in the leg was slowed down,” Frank explains.

The researchers observed that the ant-assisted amputations took about 40 minutes, which explains why the insects seemed to opt for femur amputations but not tibia amputations.

“So, because they are unable to cut the leg quickly enough to prevent the spread of harmful bacteria, the ants try to limit the likelihood of a fatal infection by spending more time cleaning the shin wound,” Keller said.

Researchers are still trying to piece together the complex pieces that underlie this seemingly innate behavior of ants.

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

These amputations are considered altruistic behavior because the ants must devote time and energy to helping others, Keller said.

“The fact that 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 compete with that would be the human system,” Frank said.

But Frank believes that ants don’t consciously know what to do. It may be more instinctive, a bit like humans putting their fingers to their lips after cutting themselves on paper.

“We’ll just instinctively put our finger in our mouth and suck on it, without actively thinking about applying the antiseptic proteins in our saliva to the wound to inhibit infection,” Frank said. “It’s likely the same for ants. There’s been enough evolutionary pressure for them to adopt two different behaviors when faced with two different types of wounds in order to maximize the survival of their nest mates. How they’re able to distinguish between them is another question I’m working on now.”

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

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