Communication in social insects such as ants is based on intelligent criteria that integrate information from multiple variables, but the identity of these variables has been unclear. In a brief communication in May 1 Nature, Michael Greene and Deborah Gordon from Stanford University show that cuticular hydrocarbons, which differ according to task, are used by workers of the red harvester ant to recognize the tasks of the ants that they encounter (Nature, 423:32, May 1, 2003).
Greene and Gordon studied nine mature colonies of the red harvester ant (Pogonomyrmex barbatus) at a well established study site in Rodeo, New Mexico. P. barbatus is a seed-eating, desert-dwelling species whose workers can be grouped into foragers (who collect food) and patrollers (who scout the foraging area). Greene and Gordon mimicked the flow of returning patrollers by dropping 3-mm glass beads into the nest at 10-second intervals. The beads were coated with one-ant equivalent extract of either patroller hydrocarbons, forager hydrocarbons, nest maintenance hydrocarbons, or plain solvent. They observed that task-specific cuticular hydrocarbons from patrollers were sufficient to rescue foraging activity. In addition, they showed that all of the following are necessary to stimulate foraging activity: a one-ant equivalent concentration of hydrocarbon extract, location just inside the nest entrance, sequential presentation, and the time of day at which the colony is ready to begin foraging.
"A brief encounter with a nest mate influences an ant's task decision because the encounter identifies the task of the other worker, cued by subtle features of other ants' hydrocarbon profiles… These encounters in the aggregate produce a dynamic network that regulates the colony's behavior," conclude the authors.