Individual specialisation and encounters between harvester ant colonies

This study examined how individual specialisation contributes to neighbour-stranger dis crimination in the red seed-harvesting ant, Pogonomyrmex barbatus. The following hypothesis was tested: is there a group of ants (detectives) that specialise in interacting with non-nestmates and thus have the opportunity to learn the colony-specific odour of neighbouring colonies? Encounters were staged between laboratory colonies. Ants were marked and observed in successive encounters. There is no specialisation for interaction; the results showed that all ants were equally likely to interact with non-nestmates. The frequency of fighting between P. barbatus colonies varies from day to day. The following hypothesis was tested: do some ants (fighters) specialise in fighting when they interact with non-nestmates. There is specialisation for fighting; a few ants tended to fight when they met non-nestmates. There was no day-to-day effect of encounters on the number of foragers in the laboratory arena. Without specialised detectives, neighbour recognition must arise either from frequent interactions between foragers of neighbouring colonies or from communication among nestmates about the odour of neighbours. Shifts in the number of specialised lighters present in the foraging pool may underlie the day-to-day variation in fighting intensity observed in the field.