Sub-Saharan Matabele ants are ruthless killers, raiding termite mounds two to four times each day. But every once in a while, an ant gets hurt and is hauled back home to recuperate - an astonishing insectoid behaviour unto itself. New research suggests there's even more to it than that - these ants also administer medical care to those wounded in battle.
A Matabele ant treats a wounded comrade whose limbs were bitten off during a fight with termite soldiers. (Image: Erik T. Frank)
At nearly 20mm in length, Matabele ants are among the world's largest ants. They're named after the fierce Matabele warriors, a Bantu tribe that wreaked havoc in southern Africa in the 19th century. Like their namesake, Matabele ants are formidable warriors, marching in along rows of 200 to 600 individuals toward termite-infested foraging sites.
But the termites aren't defenseless. Their soldiers are well-armoured and equipped with powerful jaws that can take a chunk out of a marauding Matabele ant. Injuries and deaths are common for members of the invading party, but as researchers from Germany's University of Würzburg discovered last year, these ants have developed a kind of search-and-rescue system to reduce fatalities.
While observing ants in Comoe National Park in Ivory Coast, the scientists learned that wounded give out a distress signal by excreting a pair of chemicals. These chemicals trigger a behaviour among the fellow soldier ants, who grab their wounded comrades and drag them back home to recover. Incredibly, upwards of 95 per cent of ants who were brought back to home base managed to recover and then participate in subsequent raids, compared to the 32 per cent of ants who died on the battlefield without any help. The researchers calculated that this rescue behaviour results in a colony that's about 29 per cent bigger than it would be otherwise.
Cool right? But as the same team of researchers now point out in the latest issue of Proceedings of the Royal Society B, there's more to the rescue than just bringing the wounded back - the Matabele ants also administer the ant equivalent of medical care. And like the search-and-rescue efforts, it's a behaviour unique to the entire animal kingdom. Except for humans, of course.
Once back at the home nest, the researchers watched as the soldier ants intensively "licked" the wounds of the injured, sometimes for several minutes. "We suppose that they do this to clean the wounds and maybe even apply antimicrobial substances with their saliva to reduce the risk of bacterial or fungal infection," said lead researcher Erik Frank in a statement.
For the study, some experiments were done in the field, such as the ones with heavily injured ants, and some in the lab, namely the observations of the wound treatment inside the nest. Both the field and lab experiments were conducted at the Comoé National Park Research Station in Ivory Coast.
Fascinatingly, the soldier ants also do some "triaging" on the battlefield - but the decision as to who lives and who dies is made by the injured ants themselves. By lashing out and struggling wildly, severely wounded ants - some missing multiple limbs - make it impossible for their would-be rescuers to help. The severely wounded ants "simply don't cooperate with the helpers and are left behind as a result," explained Frank. By doing so, they ensure that the ants who are most likely to survive are the ones who get rescued, while also making sure no unnecessary energy is expended in what would be a futile rescue.
By contrast, less injured ants "signal" their cries for help by remaining still and orienting their limbs and bodies for easy transport. This behaviour also gets them noticed by uninjured ants, and by keeping still, the ants may be localizing their chemical "save me" signal to single location.
It's a neat study, but there's still a lot of work to do. Frank's team needs to investigate the "licking" behaviour to further understand its role and function (for example, does it help with healing, or prevent further infection?), and figure out how the ants are so good at pinpointing the location of an injured comrade.
For ants, this Borg-like behaviour makes a lot of sense. Understanding the behaviour of the single individual can only be understood in the context of the whole; by sacrificing themselves in this way, the ants are helping to preserve the strength of the entire colony.