SOS: Call the ants

Desert ants can do fancy rescue work, but for family only

View a video of the ants attempting a rescue.

ANTS TO THE RESCUE An ant held down by a nylon-thread snare and partly buried in sand struggles to escape as colony mates, dabbed with paint to distinguish them, come to the rescue. These Cataglyphis cursor ants cope with the snare by biting at it, a rescue behavior not reported before. Elise Nowbahari

Caught in a snare and half-buried in desert sand — not a problem. Call your sisters.

Desert-dwelling Cataglyphis cursor ants can do sophisticated rescue work, even trying to use their own jaws of life to chew through a trap, according to comparative psychologist Karen Hollis of Mount Holyoke College in South Hadley, Mass. These ant rescue workers not only dig away sand and tug at the limbs of a half-buried victim but also cope with snares, biting at nylon lines that researchers use to tie down a luckless nestmate.

Yet the ants go to all this trouble for family members only, Hollis and colleagues in France report online August 11 in PLoS ONE. Trapped ants from a neighboring colony of the same species can struggle all they want, but the potential rescue workers don’t help.

“While researchers in the area of behavior and evolution have long studied altruism, controlled experimental work on rescue behavior is very rare — almost nonexistent,” comments behavioral ecologist Lee Alan Dugatkin of the University of Louisville in Kentucky. “This works suggests that we may be underestimating the extent of rescue behavior in the wild.”

Scientists have not documented much rescue work by animals, Hollis says. But by rescue work, she’s not talking about parental behavior. At any given instant, parents of thousands of species across the planet are pulling their hapless young out of some jam or other. Rescue in the researchers’ sense means one adult coming to the aid of another in dire peril. “Helping behavior is everywhere,” Hollis says, but so far she and her colleagues have found records of only two vertebrate rescue behaviors: dolphins helping an ailing member of the species up to the surface to breathe, and a white-faced capuchin monkey aiding a beleaguered colleague in a fight.

Apart from those examples, ants are the model rescuers. Since 1874 biologists have reported rescuers of several ant species digging out a buried ant and pulling at its limbs.

To test for more complex behavior, Hollis and coauthors at the University of Paris XIII challenged the rescuers by restraining each of their victims in the sand with nylon thread anchored to a disk of filter paper. In a series of tests, researchers partly buried a snared ant and released five potential rescuers nearby.

When the rescue party came from the same colony, at least some of its members went over to the struggling ant, pushing away sand and biting repeatedly at the very strong nylon snare. Other victims just elicited indifference or aggression.

If researchers anesthetized the snared ant by chilling it, rescue parties never arrived. Hollis concludes that the trapped ant must call for help, possibly by releasing a pheromone. That call could be specific to a particular colony, she says. A trapped ant from a neighboring colony didn’t seem to be getting a relevant message across to the free-roaming ants.

Potential rescuers didn’t even investigate the stranger’s crisis. “It’s not as if they touched and said, ‘Ugh, you’re not my sister, I’m leaving,’” Hollis says.

The slave-making ants Formica sanguinea have their own variation on these rescues, says Ewa Godzińska of the Polish Academy of Sciences in Warsaw. She and her colleagues have reported that within a colony, both the slave-makers and their slaves (of another species) will rescue slavemasters from traps of predatory ant lions. Yet slavemasters do not reciprocate for trapped slaves.

Save Our Sister from Science News on Vimeo.

After several minutes, colony mates are gathering around a Cataglyphis cursor that researchers have tied down with nylon thread. Rescuers drag away bits of sand to uncover the trapped ant’s body and pull on her legs as if trying to yank her free of the sand. As ants uncover the hard-to-see nylon snare around the middle of her body, they bite it.

Credit:  Nowbahari et al.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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