Behavioural ecology of mass recruitment in the army ant Neivamyrmex nigrescens

The successful rearing of the army ant Neivamyrmex nigrescens in the laboratory has enabled us to demonstrate that the pheromone trail deposited by recruiting workers is qualitatively different from the ants' exploratory trail. The recruitment trail alone can initiate as strong a mass recruitment response as can a recruiting worker that physically interacts with nestmates. The rapidity with which workers are aroused is due to secondary recruitment. Army ants are able to assemble a critical striking force before food is located, as a result of mass recruitment to new terrain. In addition to feeding behaviour, mass recruitment occurs when army ants emigrate to new nests. In both behavioural contexts, primary and secondary recruiters run more rapidly than exploring ants, and with exaggerated vertical motor patterns.