Structural organization and cohesiveness of foraging groups in Camponotus sericeus (Fabricius) (Hymenoptera: Formicidae): locally regulated or self-organized?

Abstract

BackgroundIn Camponotus sericeus (Fabricius), foraging ants are recruited mostly as individuals but occasionally as small groups that move in a single file. We studied the structure and organization of these small foraging groups and attempted to understand the process through which the cohesiveness of the moving file is maintained.ResultsThe recruited group moves in a single file as if steered by a leader at the moving tip. Ants in the group were found to exhibit certain fidelity to their respective positions in the file, despite the occasional breakdown of the cohesiveness due to disturbance and or obstructions on their path. This fidelity decreases from both ends towards the middle part of the file. Accordingly, three segments could be recognized in the moving file: (a) the leading ant that almost always maintains its position and steers the group, (b) a short tail part with a few ants that always trail the file and, (c) the mid part that binds the group; ants in this segment always tend to follow the leader through a cascading chain of tactile communication. If the leader ant is removed, entire group loses its orientation and enters into a chaotic search state. But removing any other ant does not affect the cohesiveness; rather it’s position is occupied by the member preceding it and thus maintains the link in the group.ConclusionsThe cohesiveness of the moving group appeared to result from (a) regulation of the movement of the group by the leading ant, and, (b) an interactive process among the rest of the ants. Based on these two elements, a simple automated model of the group’s movement was developed that could effectively mimic the observed pattern. We also provide evidence to suggest that recruitment of groups occurs in the direction of, and in response to, the information received by the colony on, the resource rich patches.