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Humans aren’t the only ones who can perform life-saving amputations.
Florida carpenter ants have been observed biting off injured limbs of nestmates, depending on the location of the wound, to help them survive, according to a new study.
The researchers found that about 90% to 95% of the amputated ants survived the surgery and continued to function in the nest just fine despite the loss of their leg.
of studyThe paper, published Tuesday in the journal Current Biology, Previous findings published in 2023 by the same international team of scientists.
The study found that another ant species, called the Matabele ant (Megaponera analis), uses its mouth to secrete an antibacterial compound to clean wounds and prevent potential infections. The compound is produced by a gland called the mesopleural gland.
Most ants have these glands, but over time, some species, including Camponotus floridanus, also known as the carpenter ant, have lost these glands during evolution.
Most ant species that don’t have a metathoracic gland are arboreal, meaning they live in trees, said Eric Frank, a behavioral ecologist at the University of Würzburg in Bavaria, Germany, and lead author of the study.
“We suspect that their arboreal lifestyle may put them less exposed to pathogens than subterranean colonies,” Frank said.
Frank and his colleagues had planned to continue studying Matabele ants from Côte d’Ivoire when the pandemic hit, so the team switched to studying common carpenter ants that were available in the lab.
“We wanted to see how an ant species that can’t use antibacterial compounds to treat wounds would care for its wounded,” Frank said.
The researchers were unprepared for what they observed: a type of surgical intervention previously seen only in humans.
The reddish-brown, 1.5-centimeter-long (about three-fifths of an inch) carpenter ants build nests in rotting wood throughout the southeastern U.S. They must defend their nests from rival ant colonies, sometimes resulting in injury.
Study co-author Danny Buffatto, a graduate student at the University of Lausanne in Switzerland, first observed the ants cleaning the wound and performing the amputation procedure.
“What surprised me most was the fact that they were performing amputations in the first place,” Frank says. “I never expected this, and in fact didn’t believe it when our (master’s student) Danny Buffatto first described the behavior to me. It wasn’t until he showed me the video that I was truly grateful for what we’d stumbled upon.”
Bad Zielstra
One carpenter ant can be seen cleaning the wound of another ant.
As the team observed the ants’ behaviour, Dr Laurent Keller, an evolutionary biologist at the University of Lausanne and lead author of the study, noticed another surprise: the ants only performed the amputation if the injury occurred at the femur. After biting off the leg, the ants used their mouthparts to lick and clean the wound, presumably to remove bacteria.
But if the injury is on the lower leg, i.e. the tibia, the ant will simply intensively lick the wound, and the chances of survival will be 75%.
To understand why the ants perform such special procedures, and to recreate the wounds in the lab, the researchers removed one ant from a colony of 200 tiny ants from its nest and deliberately cut the ant’s legs with micro-scissors.
“Place the ants on ice for a few minutes beforehand to allow them to calm down and be easier to handle,” Frank says. “Carefully remove an ant from the nest, place it on ice and amputate its legs. Once the ant wakes up again (after a few more minutes), return it to the colony to reunite with its nest mates.”
Among ants with injuries to the femur or tibia that were not treated alone, fewer than 40% and 15% survived, respectively.
The team also carried out CT scans of the ants to examine the insects’ injuries in more detail.
And how does the ant’s body react? The ant’s thighs have many muscles,
The ant has a blood-like fluid called hemolymph circulating through it.
Besides the heart, there are multiple cardiac pumps and muscles throughout the body that perform the same function.
Frank said injuries to the thighs restrict circulation and reduce blood flow, meaning bacteria can’t circulate through the body as quickly as the wound, and amputation helps prevent bacteria from spreading throughout the animal’s body.
Bad Zielstra
After wounding the thigh, the ant bites off the leg of another ant.
On the other hand, ants’ lower legs lack the muscles necessary to circulate blood, but if a wound is made there, bacteria can quickly get into the body and there is no time to amputate it.
“Injuries to the tibia mean that hemolymph flow is less disrupted, allowing bacteria to enter the body more quickly, whereas injuries to the femur mean that blood circulates more slowly in the leg,” Frank said.
The researchers observed that the ant-assisted amputation took approximately 40 minutes to complete, which is why the ants appear to have chosen to amputate the femur rather than the tibia.
“So because the ants can’t cut their legs fast enough to prevent the spread of harmful bacteria, they take their time cleaning the wound in their shins to limit a potentially fatal infection,” Keller says.
Researchers are still working to unravel the complex mechanisms behind this seemingly innate ant behavior.
“Worker ants must have learned over the course of evolution that amputation is an efficient way to prevent infection and increase colony productivity by increasing the number of workers available to contribute to colony tasks,” Keller says.
Keller said these amputations are considered altruistic behavior because ants have to spend time and energy helping other ants.
“The fact that ants can diagnose a wound, determine if it’s infected or sterile, and then treat it accordingly over a long period of time with other individuals — the only medical system that could match that would be the human medical system,” Frank said.
But Frank said he doesn’t think the ants consciously know what to do — rather, it may be more instinctual, like when a human puts their finger to their lips after cutting themselves with paper.
“We instinctively just put our fingers in our mouths and suck them, without actively trying to smear the antiseptic proteins in our saliva on the wound to prevent infection,” Frank says. “Ants are probably similar. The reason there was such strong evolutionary pressure for ants to exhibit two different behaviors for the two types of wounds is to maximize their chances of survival. How ants can distinguish between the two types of wounds is another question, and one I’m currently working on.”
Now the researchers hope to find more examples of wound-dressing not just in ants, but across the animal kingdom.
“We will continue to study wound-care behavior in other ant species to try to understand its evolutionary origins,” Frank says. “What was ancestral wound-care behavior like? Why do some ants amputate and others use antimicrobials?”