TRAILS AND U-TURNS IN THE SELECTION OF A PATH BY THE ANT LASIUS-NIGER

A series of laboratory experiments show how colonies of the ant Lasius niger systematically select the shorter of two paths of varying length and form between nest and foraging area, and do so with a large majority of foragers. Three different mechanisms were considered to contribute to this selection, and were evaluated by comparing mathematical models with experimental data. Bi-directional trail laying was shown to contribute much less than U-turns, where the proportion of ants that turned back depended on the path's geometry and length, and also on the trail strength. A strong modulation of the amount of pheromone deposited per ant as a function of the path's geometry was found. This modulation can also contribute to the selection of the shorter branch in the experiments where the rate of U-turns is initially the same. The selection of the path is shown to be a collective process whereby trail laying and following amplifies small initial differences in the traffic on each path caused by these three mechanisms. The foragers show no significant tendency to follow the path they used previously. © 1992 Academic Press Limited.