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Not only humans are able to perform amputations and thus save lives.
According to a new study, carpenter ants from Florida have been observed biting off injured limbs of their nestmates – depending on the location of the wounds – in order to help their fellow ants survive.
The researchers found that about 90 to 95 percent of amputees survive the procedure and can easily carry out their tasks in the nest despite the loss of a leg.
The study, published Tuesday in the journal Current Biology, builds on earlier findings published in 2023 by the same international team of scientists.
This research found that another species of ant, the Matabele ant or Megaponera analis, secretes antimicrobial substances through its mouth to clean injuries and prevent possible infections. The substances 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 in the course of evolution.
Most ant species without metapleural glands are arboreal, meaning they live in trees, said lead study author Erik Frank, a behavioral ecologist at the University of Würzburg in the German state of Bavaria.
“We believe that their arboreal lifestyle exposes them to fewer pathogens than colonies that live underground,” Frank said.
When the pandemic hit, Frank and his colleagues wanted to further study the Matabele ants in Côte d’Ivoire, so the team focused on studying the common carpenter ants that were available in their lab.
“I wanted to see how a species of ant that cannot use antimicrobial compounds to treat wounds cares for its injured,” Frank said.
The researchers were not prepared for what they observed: it was a surgical procedure that had previously only been observed in humans.
Reddish-brown Florida carpenter ants, which grow to about 1.5 centimeters long, nest in decaying wood throughout the southeastern United States. They must defend their nests against rival ant colonies, which can result in injury.
The study’s co-author, Dany Buffat, a doctoral student at the Swiss University of Lausanne, first observed the ants cleaning wounds and performing amputations.
“The biggest surprise, of course, was the fact that they were performing amputations at all,” Frank said. “I never expected that, and when our (master’s student) Dany Buffat first described the behavior to me, I couldn’t believe it. It wasn’t until he showed me the videos that I really realized what we had stumbled upon.”
Bart Zijlstra
You can see a carpenter ant cleaning the wound of another ant.
As the team watched the ants in action, lead study author Dr. Laurent Keller, an evolutionary biologist at the University of Lausanne, noticed another surprise: The ants only performed amputation when the leg injuries occurred on the thigh or femur. After biting off the leg, the ants licked the wound clean with their mouthparts, likely removing bacteria.
However, if the injury were on the lower leg, i.e. the shinbone, the ants would only lick the wound intensively, which would result in a survival rate of 75 percent.
To understand why the ants were so selective in their attack on injuries and to recreate the injuries in the laboratory, the researchers removed a single ant from the nest in small colonies of 200 ants and made controlled cuts in the ant’s leg using micro scissors.
“We would first put the ant on ice for a few minutes to calm it down and make it easier to manipulate,” Frank said. “We would carefully remove an ant from the nest, put it on ice, and then cut its leg. Once the ant woke up (after another few minutes), it would be released back into the colony to be with its nestmates.”
Among ants with thigh or shin injuries that were not treated in isolation, less than 40% or 15%, respectively, survived.
The team also conducted CT scans of the ants to further examine the insects’ injuries.
and how their bodies react to it. A variety of muscles in the thighs of the ants ensure that a
Fluid similar to blood, called hemolymph, circulates. While ants do not have human-like
Hearts, they have multiple heart pumps and muscles throughout the body that perform the same function.
Injuries to the thigh impede this circulation, Frank says, and because blood flow is reduced, bacteria cannot circulate from the wound throughout the body as quickly, meaning amputation can prevent the spread of bacteria throughout the ant’s body.
Bart Zijlstra
An ant bites off another ant’s leg after it sustained a thigh injury.
The ants’ lower legs, on the other hand, do not have muscles that are necessary for blood circulation. However, a wound there would quickly introduce bacteria into the body and there would be no time for amputation.
“In shin injuries, the flow of hemolymph was less obstructed, which meant that bacteria could enter the body more quickly. In thigh injuries, on the other hand, the rate of blood circulation in the leg was slower,” said Frank.
The researchers found that amputations with the help of the ants took about 40 minutes. For this reason, the insects apparently opted for a thigh amputation rather than a tibia amputation.
“Unable to cut open the leg quickly enough to prevent the spread of harmful bacteria, 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 decipher the complexity of this seemingly innate ant behavior.
“Over the course of evolution, workers must have learned that amputation is an effective method of preventing infection and increasing the productivity of the colony because it allows more workers to contribute to the colony’s tasks,” Keller said.
These amputations are considered altruistic behavior because the ants have to spend time and energy helping others, Keller said.
“The fact that ants are able to diagnose a wound, determine whether it is infected or sterile, and treat it accordingly over long periods of time is unmatched by other individuals – the only medical system that can compete with it is the human one,” Frank said.
However, Frank does not believe that the ants consciously know what to do. Rather, it may be more of an instinctive action, similar to how people put their fingers to their lips when they cut themselves on paper.
“We just instinctively put our finger in our mouth and suck it, without actively thinking about wanting to apply the antiseptic proteins in our saliva to the wound to prevent infection,” Frank said. “It’s probably similar in ants. There was a strong enough evolutionary pressure that they showed two different behaviors when faced with two different types of wounds to maximize their (nestmates’) chances of survival. How they can tell them apart is another question I’m currently working on.”
Now the researchers want to find further examples of wound care, not only in ants, but in the entire animal kingdom.
“We will continue to study wound care behavior in other ant species and try to understand its evolutionary origins,” Frank said. “What was the original wound care behavior? Why do some amputate while others use antimicrobials?”