John Mirenda

Army Ants on the Move: Relation Between Food Supply and Emigration Frequency

Underfed colonies of Neivamyrmex nigrescens in the laboratory emigrated on 62 percent of the nomadic days, as compared with only 28 percent for overfed colonies. Because the emigration frequency in the field is similar to that of underfed colonies, nomadic raids may not bring in enough food to satiate the larval broods. Since emigrations take time away from raiding, the food-related mechanism underlying emigrations may have evolved under more stringent ecological conditions.

Precocial behaviour of callow workers of the army ant Neivamyrmex nigrescens: Importance of stimulation by adults during mass recruitment

Abstract Callows of the army ant Neivamyrmex nigrescens do not participate in predatory raids until 3 to 7 days after their eclpsion. Within 24 h after their eclosion, however, the entire callow population joins with the adult ants in emigrating to a new nesting site. This emigration is accomplished by mass recruitment of the callows by the mature adult workers. Tests show that adults use mechanical stimulation to arouse callows to trail-following. Callows remain in the nest during raiding because their central location effectively sequesters them from the excitatory effects of the adult workers. The early participation of callows in the predatory raids suggests a precocial development that might have evolved as an adaptation for group predation and nomadic emigrations.

Army ants do not eat and run: influence of food supply on emigration behaviour in Neivamyrmex nigrescens.

Abstract Laboratory studies show that the amount and location of food strongly influence the frequency and direction of emigrations. For two overfed colonies, emigrations occurred on only 28% of the nomadic days. By contrast, underfed colonies emigrated on 62% of the nomadic days. In addition, overfeeding kept one colony from emigrating for seven consecutive days, as compared with a maximum of two consecutive days for the underfed colonies. Most emigrations took place in the direction of booty location. It was shown, however, that colonies can also recruit and emigrate to suitable nests, independent of the presence of food.