The significance of body size in territorial interactions of male beewolves (Hymenoptera: Sphecidae, Philanthus)

Abstract

In many species of the sphecid wasp genus Philanthus, males defend their mating territories. Field observations on three species, Philanthus crabroniformis, P. pulcher, and P. psyche, demonstrated that size differences among males influenced the outcome of competition for territories. Body size varies considerably within males of all three species. In P. crabroniformis, 100%, and in P. pulcher, 97% of aggressive interactions on territories were won by the larger of the two contestants. I captured resident males from territories, and then monitored for the arrival of replacement males. These manipulations yielded several interesting results: (1) individuals from large pools of non-territorial males quickly assumed possession of abandoned territories, (2) the original residents removed from territories were significantly larger in mean body size than those that replaced them, and (3) only 8% of the replacing males were larger than the orginal resident of the territory. The results suggest a sizeconditional strategy in which larger males defend or usurp territories and smaller males opportunistically take over territories that have been abandoned (e.g. the resident leaves to feed or is preyed upon).