Peer into the deep recesses of an ant colony and you'll discover an extremely well organized community with thousands of workers quietly going about their jobs. Some dig nests while others gather food or tend the young. Remarkably, every chore is done without supervision or direction, and some workers even switch jobs to meet the ever-changing needs of the colony.

How does an insect with a brain the size of a poppy seed decide to carry out a particular task? The answer, says a team of Stanford University biologists, has less to do with brainpower than with the ant's extraordinary sense of smell. The scientists found that, when a parade of patroller ants returns to the nest, their distinctive body odor cues other workers to go out and forage for food. This new insight into the behavior of social insects is the latest discovery to emerge from a 20-year field study of red harvester ants (Pogonomyrmex barbatus) in the southern Arizona desert - a project designed and led by Deborah M. Gordon.

"Ants use chemicals the way we human beings use sight and sound. That's how they get the majority of the information about what's going on in their environment," said Stanford postdoctoral fellow Michael J. Greene. "Tactile, or touching, information is important to them, too, but for most ants, vision is not." An ant's antennae are extraordinarily fine-tuned to differentiate subtle smells produced by hydrocarbons. The waxy outer surface of an ant's body contains about 25 different hydrocarbons, which emit slightly different odors that are imperceptible to people, but to an ant provide important information about life in the colony. "Subtle changes in the concentration of these relatively simple chemicals can produce very important and profound behavioral changes in ants," Greene noted.

"An ant can assess the tasks of another ant using hydrocarbons that are specific to that task. It's not an intellectual achievement; it's a perceptual achievement. The ant doesn't have to think to get the difference between one hydrocarbon and another. It just has to have the right receptors to smell the difference," explained Gordon. Ants do not tell each other what to do when they meet, she emphasized: "What seems to matter to an ant is the pattern of interactions it experiences rather than a particular message or signal transferred at each interaction."

Understanding the subtle cues and interactions that enable small-brained insects to build elaborate communities has become a major area of research, not only for biologists but also for engineers trying to solve intricate problems in computer science, network communications and even robotics. Greene and Gordon's study, "Cuticular Hydrocarbons Inform Task Decisions," appeared in the May 1 edition of Nature. >from *'Work stinks': It's more than just a slogan among ants, researchers find*. april 30, 2003

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> a poppy seed brain?