Ant Iron Chefs: Larvae fix dinner but don't sneak snacks
[Science News 2005-12-24]

[Photo] ROLE PLAYING. Adults with large heads defend the Pheidole spadonia colony, and the smaller, millimeter-long workers cut up meat from prey and tend the young. The chubby, translucent larvae marinate meat in their digestive juices before the workers distribute it.
N. Buck


Susan Milius

New videos of ants fixing an entr??e of fruit fly stew show that it's the youngsters who do the colony's version of cooking. What's more, they don't nibble as they cook but wait to be served their fair share.

Ants prepare their meat not by heating but by marinating it with digestive enzymes to create a glistening protein slurry. With their hourglass figures, adult ants have such tiny waists that solid food can't pass through to their abdomens. Biologists already knew that the blob-shaped larvae predigest meat. Some scientists had suggested that the adults feed meat to the larvae and return later for some regurgitated protein slurry.

That's not what happened, though, in videos of lab colonies of pinhead-size Pheidole spadonia, says Deby Cassill of the University of South Florida in St. Petersburg. Adults placed lumps of prey in little hairy depressions on top of the larvae's bellies, and for some 5 hours, larvae drooled digestive enzymes over the meat as it dissolved into a protein drink. The adults collected the slurry to distribute, but during the kitchen prep, the youngsters rarely took a swallow themselves.

The larvae "truly are performing a colony-level task, not a selfish one of eating," comments social-insect biologist Joan Herbers of Ohio State University in Columbus.

Colonies of P. spadonia have two worker castes: soldiers with huge jaws and smaller workers. Soldiers don't tend larvae or fix food. "Like our military, they are maintained and fed by tax dollars," says Cassill.

Coauthor Diana Wheeler of the University of Arizona in Tucson had caught local P. spadonia ants after their mating flights and established several colonies. Cassill selected descendants of those ants and set up observation nests containing 25 of the smaller workers and 30 of the oldest larvae. She fed the new colonies sugar water and a daily fruit fly and managed six times to videotape the food preparation.

When their daily meat arrived, adult workers discarded the fruit fly's wings within seconds. The adults carved the carcass into hunks and then tamped them into external depressions on the bulging bellies of the gourd-shaped larvae. The workers checked back frequently to slurp off liquid and shift chunks among larvae.

Cassill dyed some pieces of fruit fly with green food coloring to see when the translucent larvae swallowed food. They rarely consumed any of the slurry as they tended it, Cassill and her colleagues report in the most recent (November) issue of Insectes Sociaux. However, the larvae did eat protein slurry out of the mouths of adult workers.

"Larvae are a fully functioning caste," performing a job to benefit the entire colony, just as the soldiers and small workers do, says Cassill.

Ant specialist Bert H??lldobler of the University of W??rzburg in Germany points out that weaver ants also use child labor. To make their elaborate leaf tents, workers manipulate larvae "like living [silk-]spinning shuttles," he says.