Trail Patterns and Movement of Workers Among Nests in the Ant Formica Obscuripes (Hymenoptera: Formicidae)

Abstract

Workers of the ant Formica obscuripes Forel, at a site in southwestern Montana [USA], used a system of trails to travel between different nest mounds and between nests and foraging areas (primarily patches of plants bearing honeydew secreting Membracidae and Aphididae). Different groups of nests, served by non-overlapping systems of trails, apparently consituted polydomous colonies. Movement of workers among mounds was non-random both within and between nest groups. In a mark-recapture study, 97% of the workers recaptured on nests other than those on which they were marked were found on mounds within the same trail system. Experiments in which workers were transferred between mounds demonstrated that ants tolerated workers from mounds within their own nest group, but usually acted aggressively towards workers from other nest groups. The trail patterns remained stable during the three-month study and connected nests up to 135 m apart. The results are compared to those obtained in other studies of Formica.