No Ant Left Behind: Ants will rescue wounded colony mates

The phrase “army ant” has been used to describe multiple species of these social insects, and based on the behavior of the Megaponera analis, it isn’t difficult to see why – these well-trained warriors are committed to ensuring that no man gets left behind, according to a new study.

As Erik Frank, a doctoral student at the University of Würzburg in Germany, and his colleagues reported this week in the journal Science Advances, hundreds of these large, black, termite-eating ants (which are native to sub-Saharan Africa) march into formation when hunting for food.

A total of 200 to 500 ants travel together in rows of three in a two-meter long column that “looks like a long snake walking on the ground,” Frank told NPR on Wednesday. “And after roughly 20 minutes the battle is over… and the ants start collecting the termites to return.”

However, he said that a few years ago, he first noticed that some of the ants returning home after engaging in combat were carrying other ants instead of termites. Curious as to what the ants were doing, he investigated further, and found that the ants were rescuing their injured colleagues.

“This is not an altruistic behavior. The ants do not help the injured out of the goodness of their hearts,” Frank explained to Reuters. “There is a clear benefit for the colony: these injured ants are able to participate again in future raids and remain a functioning member of the colony.”

‘Illogical’ behavior benefits the colony, say authors

While observing that some ants became injured during their battles with the termites, the study authors marked these wounded warriors with paint, and found that in nearly every instance, they were able to make a full recovery and return to action – sometimes within a matter of hours!

Frank’s team also conducted an experiment to see what would happen to the injured ants if they were not rescued. The results, NPR noted, were not good: the wounded ants were unable to move fast enough to keep up with the group, fell behind and were ultimately devoured by predators.

Similar behavior has been observed in primates and some other species of mammals (including dolphins and elephants), but Frank told Reuters that it had initially “sounded illogical” that ants would have developed such a behavior. However, “after a closer look, we realized that the good of the individual, saving the injured, can also be for the good of the colony,” he added.

An injured ant, as it turns out, will excrete a chemical signal to let its mates know that it has been hurt, said National Geographic. In fact, when the researchers isolated this chemical, then applied it to healthy ants, they discovered that the uninjured insects were also “saved,” indicating that the so-called rescuers may not even be fully aware that their kin had been wounded.

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Image credit: Erik Frank

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