Injured African ants brought back to nest to recover

This February 2018 video is called These Ant Paramedics Save Their Injured Comrades.

Another video used to say about itself:

No Ant Left Behind: Warrior Ants Carry Injured Comrades Home

12 April 2017

Leave no man behind. That’s an old idea in warfare — it’s even part of the Soldier’s Creed that Army recruits learn in basic training.

And never leaving a fallen comrade is also the rule for some warriors who are ants, according to a report published Wednesday in the journal Science Advances.

These ants, Megaponera analis, hunt and eat termites. Scouts will go out, find a group of termites, and then return to the ant nest to muster the troops.

Biologist Erik Frank explains that 200 to 500 ants will march out in formation. “Like three ants next to each other, in a 2-meter-long column,” he says. “It’s very peculiar and it looks like a long snake walking on the ground.”

When the termites spot this invading army, they try to escape, but the fighting is fierce.

“And after roughly 20 minutes the battle is over,” says Frank, a doctoral student with the University of Würzburg in Germany who is researching animal behavior and evolution. “You have a lot of termites lying dead on the ground,” he says, “and the ants start collecting the termites to return.”

A few years ago, Frank was working at a field station in the Ivory Coast when he noticed that some of the ants marching home after battle weren’t carrying termites. Instead, they were carrying other ants.

“And I was wondering, ‘What exactly was going on there? Why were they carrying some of the ants?'” he recalls.

It turns out, those transported ants weren’t dead — they were injured.

Ants sometimes lose a leg or two, which makes it hard for them to walk. Or, they can be weighed down by a dead termite whose jaws had clamped onto them. Either way, they’re slower than uninjured, unburdened ants.

By marking these injured ants with paint, Frank learned that in nearly all cases, they made a full recovery after being carried home to recuperate. They learn to walk with fewer legs, and their ant buddies apparently will pull off stuck termites. It doesn’t take long for an ant that’s been hurt to once again be ready for action.

Credit: Frank et al./Science Advances

“We saw them again, participating in hunts the next day,” says Frank.

He and his colleagues did some experiments to see what would happen to injured ants that weren’t carried home. It turns out that these poor ants couldn’t march fast enough. So they fell behind — and frequently got eaten by spiders and other predators, the researchers report.

From Science Advances:

Saving the injured: Rescue behavior in the termite-hunting ant Megaponera analis

Erik Thomas Frank, Thomas Schmitt, Thomas Hovestadt, Oliver Mitesser, Jonas Stiegler and Karl Eduard Linsenmair

12 April 2017

Abstract

Predators of highly defensive prey likely develop cost-reducing adaptations. The ant Megaponera analis is a specialized termite predator, solely raiding termites of the subfamily Macrotermitinae (in this study, mostly colonies of Pseudocanthotermes sp.) at their foraging sites.

The evolutionary arms race between termites and ants led to various defensive mechanisms in termites (for example, a caste specialized in fighting predators). Because M. analis incurs high injury/mortality risks when preying on termites, some risk-mitigating adaptations seem likely to have evolved.

We show that a unique rescue behavior in M. analis, consisting of injured nestmates being carried back to the nest, reduces combat mortality. After a fight, injured ants are carried back by their nestmates; these ants have usually lost an extremity or have termites clinging to them and are able to recover within the nest.

Injured ants that are forced experimentally to return without help, die in 32% of the cases. Behavioral experiments show that two compounds, dimethyl disulfide and dimethyl trisulfide, present in the mandibular gland reservoirs, trigger the rescue behavior.

A model accounting for this rescue behavior identifies the drivers favoring its evolution and estimates that rescuing enables maintenance of a 28.7% larger colony size. Our results are the first to explore experimentally the adaptive value of this form of rescue behavior focused on injured nestmates in social insects and help us to identify evolutionary drivers responsible for this type of behavior to evolve in animals.