African Matabele ants are fighters — several times a day, they leave their nests on raids, battling termite soldiers and dragging termite workers home for dinner.
They drag their fallen comrades back, too, bodies maimed by termite jaws.
Now German biologists have discovered what happens at the end of those rescue operations: Back at the nest, ants act as medics, cleaning the wounds of injured ants — and reducing their mortality rates in the process.
The "organized social wound treatment" is described in a study published Wednesday in the Proceedings of the Royal Society B. The research team, from Julius Maximilian University of Würzburg (JMU) in Bavaria, also shared videos of ants examining injured colleagues in the field, and cleaning the wounds upon return to the nest.
Scientists already knew that Matabele ants would carry wounded ants back from raids, as NPR reported last spring.
Now researcher Erik Frank, along with Marten Wehrhahn and K. Eduard Linsenmair, has discovered a sort of triage is involved.
"Heavily injured ants" — with five limbs missing — were left to die. It wasn't the able-bodied ants were making the call, however. The badly injured ants would flail around and not cooperate with any attempts to move them, essentially forcing their would-be rescuers to leave them behind.
"Lightly injured ants," meanwhile, would act more injured when there were nestmates nearby to help save them. Once they had the attention of uninjured ants, they would cooperate with rescue efforts by making themselves easier to carry.
Then, once the whole group was back at the nest, medical treatment began.
"The ants treat the open wounds of their injured fellows by 'licking' them intensively, often for several minutes," JMU explained in a press release.
"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," Frank said in the statement.
And the treatment works.
"If they don't receive the treatment, 80% die within 24 hours," Frank told The Guardian. "If you allow the treatment for an hour, the ants survive."
Specifically, the mortality rate for ants whose wounds were cleaned by their nestmates fell to just 10 percent.
Once recovered, ants missing limbs can "reach running speeds similar to healthy ants," Frank told New Scientist.
It's important to keep those wounded ants alive to hunt again, as Live Science reports:
[T]he tendency is to think that ant individuals are easily replaced cogs in the machinery of the colony, [Frank] said. But in M. analis, colonies aren't that large, and only a dozen or so baby ants are born each day ...
" 'Losing one or two ants each day would be quite significant, so they really have to find ways to reduce the mortality in that sense,' Frank said. 'The individual does matter.' "
Frank emphasized to the Guardian that "complex and sophisticated" behaviors, like the triage and treatment of wounded nestmates, can emerge without any cognition or knowledge on the part of the individual ants.
NPR's Nell Greenfieldboyce reported on Frank's previous research, on ants carrying wounded comrades off the field.
She noted that the behavior can't really be compared to how some mammals take care of each other:
"[T]hese ants are not doing it out of the goodness of their heart," says Frank.
"He says they're just responding to a chemical signal from the injured ants, rather than being motivated by empathy.
"Peggy Mason, a neurobiologist at the University of Chicago who has studied how rats will rescue other rats from traps, says this is a great study that confirms that ants will rescue each other in certain situations.
" 'Does it remind me of mammalian helping? Well, not really,' she says, noting that the ants don't seem to be intentionally helping each other.
" 'One reason why one might think that they're not is that if they encounter that same injured ant on the way to the hunt, they ignore it,' Mason says. Wounded ants only get carried home if they're encountered after the battle.
"Rats, in contrast, seem to have some sort of emotional response that triggers helping.' "