Army ant behavior studied

SEATTLE, Dec. 15 (UPI) -- An encounter with a giant earthworm and the army ants pursuing it has resulted in a new theory about the origin of the ants' cooperative hunting behavior.

Animal behaviorist Sean O'Donnell of the University of Washington was having an afternoon cup of coffee when a giant earthworm exploded from the jungle floor in an Ecuadorian nature preserve. The nearly 16-inch-long worm was being pursued by a column of hundreds of army ants that quickly paralyzed or killed it.

That sighting, and another involving the same ant species, led O'Donnell and colleagues to offer a new theory on the origin of cooperative hunting behavior in army ants, which are among the most socially complex animals known.

O'Donnell says mass cooperative food foraging, a key element in the behavior of army ants, may have begun as a way to subdue large prey.

"Cheliomyrmex (army ants) may be telling us that cooperative hunting of large prey is an evolutionary predecessor of going after smaller prey," said O'Donnell. "Typically, army ants follow a lifestyle of attacking other social insect colonies. But Cheliomyrmex is not following this lifestyle."

The study appears in the current issue of the journal Biotropica.