Stone dropping by Conomyrma bicolor (Hymenoptera: Formicidae): A new technique of interference competition

The dolichoderine ant Conomyrma bicolor interferes with the activity of other desert ants when their nest entrances are in close proximity. C. bicolor workers surround these nests, pick up small stones and other objects with their mandibles, and drop them down the nest entrances.Interactions of C. bicolor with three species of Myrmecocystus (M. mexicanus, M. mimicus, and M. depilis) were investigated. 'Stone dropping' and associated behaviors prevent the Myrmecocystus colonies from foraging. Periodic checks throughout the summer revealed a consistently adverse effect on these Myrmecocystus species.Considerable overlap in food resources, activity times, as well as space among C. bicolor and the Myrmecocystus species suggest that 'stone dropping' is a technique of interference competition.We were not able to completely analyze the mechanism which keeps the victimized colonies from foraging. However, we report circumstantial evidence supporting the hypothesis that the stones function as a mechanical signal. The dolichoderine ant Conomyrma bicolor interferes with the activity of other desert ants when their nest entrances are in close proximity. C. bicolor workers surround these nests, pick up small stones and other objects with their mandibles, and drop them down the nest entrances. Interactions of C. bicolor with three species of Myrmecocystus (M. mexicanus, M. mimicus, and M. depilis) were investigated. 'Stone dropping' and associated behaviors prevent the Myrmecocystus colonies from foraging. Periodic checks throughout the summer revealed a consistently adverse effect on these Myrmecocystus species. Considerable overlap in food resources, activity times, as well as space among C. bicolor and the Myrmecocystus species suggest that 'stone dropping' is a technique of interference competition. We were not able to completely analyze the mechanism which keeps the victimized colonies from foraging. However, we report circumstantial evidence supporting the hypothesis that the stones function as a mechanical signal.