Ants rescue trapped relatives

In a French laboratory, a team of ants is attempting a daring rescue. One of their colony-mates is trapped in a snare - a nylon thread that dastardly researchers have looped around its waist and half-buried in some sand. Thankfully, help is at hand. A crack squad of rescuers work together to dig away at the sand, expose the snare, and bite at the threads until their colleague is liberated.

Many animals help each other but actual rescue attempts, even between individuals of the same species, are rarely documented. Among back-boned animals, dolphins are famously said to help injured comrades by supporting them at the surface so that they can breathe more easily, and a lone capuchin monkey was documented to save a mother and baby from attack by a rival group.

Then, there are ants. As early as 1874, biologists noted that ants will often dig out fellows that have sunk too deeply into sand and later studies showed that they'll also drag others out by their legs. But both limb-pulling and sand-digging are very simple actions, that could be triggered by chemical alarms released by stressed ants. You could imagine that workers have a simple programme that says "Follow the alarm smell until you find its source, then dig and pull."

But it's very hard to see how such simple rules could direct rescuers to uncover and bite through a nylon snare. These escapades show that ants can launch rescues that are more sophisticated and exact that anything previously reported.

Elise Nowbahari from the University of Paris Nord buried individuals of the desert ant Cataglyphis cursor, after knotting nylon threads knotted around the thinnest parts of their waists. Five potential rescuers were brought into play. If the captive came from the same colony, the five-ant squad always tried to rescue them, by moving sand away, biting precisely at the snare, and pulling on the prisoner's limbs.

Now, posts about insect altruism tends to attract comments from people who come over all misty-eyed and long for humans to follow in the ants' selfless example. Well if we take that sentiment quite literally, then based on the behaviour of C.cursor, we should only help people who live in our own house or flat, and brutally attack everyone else. 

Nowbahari found that the ants were very picky with their altruism, only choosing to free others from the same colony. Their behaviour towards members of other colonies, other species of ants, or tasty crickets, couldn't have been more different. The five-member squads never lifted a mandible to rescue these individuals; instead, they threatened them with open jaws, bit and dismembered them, or even sprayed them with acid.

The rescues involved a certain degree of audience participation; if the ensnared ant was chilled beforehand so that it remained still, the others didn't try to rescue it. This make sense, for studies with other species show that actively struggling individuals release a pheromone that attracts help. This cue probably contains a chemical component that is unique to each colony and that allows the ants to decide who is closely related enough to themselves to warrant a rescue.

Reference: Nowbahari, E., Scohier, A., Durand, J., & Hollis, K. (2009). Ants, Cataglyphis cursor, Use Precisely Directed Rescue Behavior to Free Entrapped Relatives PLoS ONE, 4 (8) DOI: 10.1371/journal.pone.0006573

More on ants:

The signals of life - ants use chemical messages to avoid getting trashed

Army ants plug potholes with their own bodies

Butterflies scrounge off ants by mimicking the music of queens