Animal behaviorist Sean O'Donnell was having an afternoon cup of coffee when a giant earthworm exploded out of the leaf litter covering the jungle floor in an Ecuadorean nature preserve. The worm, later measured at nearly 16 inches long, was pursued by a column of hundreds of raiding army ants that quickly paralyzed or killed it.
That sighting, and another involving what turned out to be the same species of army ant feeding on the carcass of a snake, has led O'Donnell of the University of Washington and several 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.
Writing in the current issue of the journal Biotropica, O'Donnell and biologists Michael Kaspari of the University of Oklahoma and John Lattke of Universidad Central de Venezuela, propose that mass cooperative food foraging, a key element in the behavior of army ants, may have begun as a way to subdue large prey.
The species that O'Donnell observed is called Cheliomyrmex andicola and it lives mainly underground in New World tropical rainforests. It had been previously identified, but little was known about its behavior or prey until the two chance encounters at the Tiputini Biodiversity Station, an ecological preserve in eastern Ecuador.
The ants are brick red in color and their size would be considered medium or large when compared to most common ant species found in United States. What makes Cheliomyrmex such a fearsome predator is that its workers have claw-shaped jaws that are armed with long, spine-like teeth. These teeth may serve to help Cheliomyrmex workers attach themselves to their prey's skin during attack
O'Donnell, who was bitten and stung when he collected Cheliomyrmex specimens, said the ants' stings were particularly painful and itchy, comparable to the stings of fire ants. He and his colleagues
Contact: Joel Schwarz
University of Washington