Hunting ants in Africa march off to raid termite nests with military precision. Now, new research finds that these ants are truly a band of brothers. They even rescue their wounded comrades.
These ant rescues aren't really selfless, researchers reported today (April 12) in the journal Science Advances. Without the fallen ants, colony sizes would probably be nearly a third smaller, because injured ants frequently die if they're not helped home.
"People always think that for ants or social insects, everything they do is for the good of the colony," said Erik Frank, a doctoral student at the University of Würzburg, in Germany, who led the research. Biologists typically downplay the importance of the individual insect, Frank told Live Science. [See Photos of Zombie Ants]
"Here we show, for the first time, an example where the good of the individual, of saving an individual ant, is good for the colony as well," Frank said.
Ants to the rescue!
Megaponera analis ants live in sub-Saharan Africa and eat termites — only termites. Multiple times a day, an ant scout will come across a foraging band of termites and rush back to its nest, recruiting as many as 500 ants to march to the termites and attack. The ants then carry the termite corpses back to the nest to feast. [Ancient Termite-Ant Warfare Locked in Amber]
But Frank noticed that some of the ants carried not dead termites, but living ants, back to the nest. Upon closer inspection, he realized that these ants were wounded. Some had lost a leg or an antenna, while others had an angry termite or two clinging to their bodies.
"What's the benefit?" Frank wondered. "Why were they even doing this?"
To find out, Frank first chose 20 random injured ants and forced them to return alone from the hunting site to their nest, without the benefit of help from their brethren. He found that 32 percent of the injured ants died on the journey. More than half (57 percent) of the injured ants that were killed were ambushed by jumping spiders because they couldn't move very quickly.
In comparison, only 10 percent of the healthy ants fell to predators on their marches back to the nest, and Frank never saw a carried ant get attacked in 420 raids.
For an injured ant, it was clearly beneficial to get rescued.
"But this is not the reason this behavior has evolved," Frank said. "It obviously needs to benefit the colony as a whole."
For the good of the group
And it does benefit the whole colony, Frank found. By marking injured ants with acrylic paint, Frank was able to track them in subsequent raids. He found that 95 percent of the time, the once-wounded ants returned to battle. In fact, 21 percent of ants in raiding parties showed signs of previous injury. Frank also found that ants with termites attached to them had those termites removed when they were safely back in the nest; ants that lost a limb or antenna spent a few hours figuring out how their bodies worked. By the next day, those amputee ants could run nearly as fast as their uninjured nest mates.