The Florida Carpenter is a rather normal ant with a particularly gory party trick. The common species native to its namesake selectively treats the wounded limbs of its fellow nestmates… by chopping them off.
In a study published in the journal Current Biology, researchers not only discovered this habit but also found that this surgery aided in the ant's recovery and that the ‘healthcare’ was personalised to each injury.
“When we're talking about amputation behaviour, this is literally the only case in which a sophisticated and systematic amputation of an individual by another member of its species occurs in the animal kingdom,” says first author and behavioural ecologist at the University of Würzburg, Dr Erik Frank.
This type of behaviour isn’t necessarily new to ants. In a paper published back in 2023, it was discovered that an entirely different group of ants, the Megaponera analis found in Sub-Saharan Africa, uses a special gland to inoculate injuries with a compound that limits possible infections.
What makes the Florida Carpenter stand out is its complete lack of tools. They appear to use only mechanical means to treat other ants.
This care comes in two forms. The ants would either perform wound cleaning with just their mouths or a cleaning followed by a complete amputation of the leg. The researchers discovered that the ants used a form of assessment to decide which option was best.
Two types of leg injuries were analysed in the study – lacerations on the femur (thigh) and those on the tibia (shin). All femur injuries were accompanied by an initial cleaning of the cut by a nestmate, followed by a separate ant chewing off the leg entirely.
Luckily for the ants with tibia injuries, only a light bit of mouth cleaning was required to treat their wounds. In both cases, intervention resulted in ants with a much greater survival rate.
“Femur injuries, where they always amputated the leg, had a success rate around 90 or 95 per cent. And for the tibia, where they did not amputate, it still achieved about the survival rate of 75 per cent,” says Frank.
In cases where help wasn’t applied, there was less than 40 per cent survival for femur injuries and 15 per cent for tibia.
The team believes that the ants were choosing paths for wound care based on the risk of infection at the wound site. Micro-CT scans of the femur showed it is mostly muscle tissue. This suggests that it is crucial for pumping blood from the leg into the main body.
An injury to the femur would mean the muscles become compromised, reducing their ability to circulate potentially bacteria-laden blood. The tibia on the other hand has very little muscle tissue and wouldn’t be as involved in blood circulation.
“In tibia injuries, the flow of the hemolymph was less impeded, meaning bacteria could enter the body faster. While in femur injuries the speed of the blood circulation in the leg was slowed down,” says Frank.
“The fact that the 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 rival that would be the human one.”
The team is now running similar experiments with other ant species to see just how conserved this behaviour is. The study also raises questions about ants' abilities to withstand pain based on the long duration of these surgeries.
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