Encounter rate and task allocation in harvester ants

As conditions change, social insect colonies adjust the numbers of workers engaged in various tasks, such as foraging and network. This process of tas k allocation operates without central control; individuals respond to simpl e. local cues. This study investigates one such cue, the pattern of an ant' s interactions with Other workers. We examined how an ant's tendency to per form midden work, carrying objects to and sorting the refuse pile of the co lony, is related to the recent history of the ant's brief antennal contacts , in laboratory colonies of the red harvester ant, Pogonomyrmex barbatus. T he probability that an ant performed midden work was related to its recent interactions in two ways. First, the time an ant spent performing midden wo rk was positively correlated with the number of midden workers that ant had met while it was away from the midden. Second, ants engaged in a task othe r than midden work were more likely to begin to do midden work when their r ate of encounter per minute with midden workers was high. Cues based on int eraction rate may enable ants to respond to changes in worker numbers even though ants cannot count or assess total numbers engaged in a task.