Risk Averse Foraging in Formicine Ants

Abstract

Ants are eusocial insects whose workers may engage in foraging as their exclusive activity for most of their adult life. Most ant communication, and thus much of the mechanism for maintenance of social organization, is thought to be chemical. When workers encounter food, they may leave pheromone trails to alert other workers to productive forage, enhancing food acquisition for the whole colony (Traniello 1989). Some ants also emit alarm pheromones in response to danger or trauma. This may elicit either swarming an attacker or escape behavior (Jackson and Ratnieks 2006). In order to examine the time-dependence of ant communication, I measured the intervals between ant visits subsequent to one worker’s discovery of a rich food source. I predicted a decreasing logarithmic curve, representing a scenario in which subsequent ants would reach the food with increasing speed. The curve would thus asymptote at some minimum interval corresponding to a maximum speed of travel for individual ants.

I also examined risk awareness. By capturing foraging ants and removing them, but depriving them of the opportunity to emit alarm pheromones, I hoped to test whether ants were aware of the disappearance of compatriots without such cues. Without these cues, I expected the rate of chance encounter to determine these intervals.