Interaction rate informs harvester ant task decisions

Social insect colonies operate without central control, andcolony organization results from the ways that individuals respondto local information. We investigated how temporal information,in particular the rate of interaction among workers, stimulatesforaging activity in the red harvester ant (Pogonomyrmex barbatus).Patrollers scout the foraging area each morning. Previous workshowed that the patrollers' safe return to the nest stimulatesthe foragers to leave the nest; if the patrollers do not return,the foragers do not emerge. Here, we tested whether contactwith returning patrollers must occur at a particular rate tostimulate foraging. We varied the rates at which we introducedpatroller mimics, glass beads coated with an extract of thecuticular hydrocarbons of patrollers. A return rate of 1 patrollermimic every 10 s stimulated the highest level of foraging activity.We found that the onset of foraging depends on the rate of patrollerreturn. Adding beads coated with patroller hydrocarbons at arate of 1 per 10 s caused otherwise undisturbed colonies toforage 17.9 ± 19.7 (standard deviation) min faster thancolonies that received blank control beads. These results showthat rate is a crucial source of information in the networkof interactions among workers.