Rules of supply and demand regulate recruitment to food in an ant society

The process by which ant scouts move a group of nestmates toward a newly discovered food site is called recruitment. In this paper, I report on the interactions between scouts and nestmates that result in a graded recruitment response to graded food quality in the fire ant, Solenopsis invicta. Twelve experimental groups composed of 100 fire ant workers and 50 fire ant larvae were established (three experimental groups per colony x four stock colonies). Each experimental group was placed in a shallow, artificial nest with a glass cover. After a 48-h period of food deprivation, experimental groups were exposed to one of three concentrations of sugar water. Behavioral interactions between scouts and nestmates in each group were videotaped at 10x magnification for 20 min. Detailed behavioral data on a total of 120 scouts (10 scouts per experimental group) and similar to1,000 nestmates (similar to90 nestmates per experimental group) were transcribed from the videotapes using standard play and frame-by-frame techniques. Throughout the recruitment process, scouts employed six discrete behaviors to inform nestmates of the location and quality of a food site. Scouts laid incoming trails, waggled their heads, increased walking tempo, stroked nestmates with their antennae, advertised with a brief food display, and led groups of nestmates to the food site by laying outgoing trails. In turn, nestmates assessed the food sample with antennae, then responded to or resisted recruitment based on the quality of food advertised, their employment status and their level of hunger. In summary, recruitment was an emergent property based on competent supply and demand decisions made face-to-face inside the nest rather than on the trail or at the food site.