Florida carpenter ants have been caught on camera amputating the infected limbs of wounded nestmates.
It is the first time any creature has been seen to carry out such an operation on a member of its own species in the animal kingdom – other than humans, say scientists.
They described how the ants – a common, brown species native to the American state – selectively treat the wounded limbs of fellow nestmates—either by wound cleaning or amputation.
When experimentally testing the effectiveness of the “treatments,” the research team found that not only did they aid in recovery, but the ants’ choice of care catered to the type of injury presented to them.
Study first author Dr. Erik Frank, a behavioral ecologist at the University of Würzburg in Germany, said: “When we’re talking about amputation behavior, 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.”
He said that wound care among ants is not an entirely new phenomenon. In a paper published last year, it was discovered that a different group of ants, Megaponera analis, use a special gland to inoculate injuries with antimicrobial compounds meant to quell possible infections.
But Dr. Frank says that what makes Florida carpenter ants (Camponotus floridanus) stand out is that because they have no such gland, they appear to be using only mechanical means to treat their nestmates
The research team discovered that mechanical care involves one of two routes. The ants would either perform wound cleaning with just their mouthparts or perform a cleaning followed by the full amputation of the leg.
To select which route they take, Dr. Frank says the ants appear to assess the type of injury to make informed adjustments on how best to treat it.
In the new study, published in the journal Current Biology, two types of leg injuries were analyzed, lacerations on the femur and those on the ankle-like tibia.
All femur injuries were accompanied by an initial cleaning of the cut by a nestmate, followed by a nestmate chewing off the leg entirely.
But tibia injuries only received the mouth cleaning. In both cases, the intervention resulted in ants with experimentally infected wounds having a much greater survival rate.
Dr. Frank said: “Femur injuries, where they always amputated the leg, had a success rate around 90% or 95%.
“And for the tibia, where they did not amputate, it still achieved about the survival rate of 75%.”
He said that compares to the less than 40% and 15% survival rates for unattended infected femur and tibia abrasions, respectively.
The research team believes that the preferred path of wound care could be related to the risk of infection from the wound site.
Micro-CT scans of the femur showed it is largely composed of muscle tissue, suggesting it plays a functional role in pumping blood, referred to as hemolymph, from the leg into the main body.
When the femur is injured, the muscles become compromised, reducing their ability to circulate potentially bacteria-laden blood. However, the tibia has little muscle tissue and so little involvement in blood circulation.
Dr. Frank said: “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.”
He says the speed at which the ants can amputate a leg makes a difference. An ant-assisted amputation takes at least 40 minutes to complete.
Experimental testing showed that with tibia injuries if the leg was not immediately removed post-infection, the ant would not survive.
Study senior author Professor Laurent Keller said: “Thus because they are unable to cut the leg sufficiently quickly to prevent the spread of harmful bacteria, ants try to limit the probability of lethal infection by spending more time cleaning the tibia wound.”
Dr. Frank said: “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.”
Keller added: “It’s really all innate behavior.
“Ant behaviors change based on the age of an individual, but there is very little evidence of any learning.”
Now the research team is running similar experiments in other Camponotus species to see just how conserved the behavior is and to begin to unpack whether all ant species without the special antimicrobial gland also perform amputation.
Dr. Frank added: “When you look at the videos where you have the ant presenting the injured leg and letting the other one bite off completely voluntarily, and then present the newly made wound so another one can finish cleaning process -this level of innate cooperation to me is quite striking.”
Produced in association with SWNS Talker
