OUTSTATIONS AS STABLE MEETING POINTS FOR WORKERS FROM DIFFERENT NESTS IN A POLYDOMOUS NEST SYSTEM OF FORMICA EXSECTA NYL. (HYMENOPTERA: FORMICIDAE)

The mound building narrow-headed ant Formica exsecta builds guarding outstations, usually at the root of the aphid-housing plants. Colonies of this species can develop into huge polydomous systems, so-called supercolonies, made up of several hundred of related nests and outstations. Although the existence of these guarding structures is well-known, still there is little information available concerning their characteristics. In the frame of this study we analyze the characteristics and the integrative role of outstations within a large polydomous system of exsecta as a function of ant nest density. The study was carried out in Transylvania, Romania. Two areas with different ant nest densities were selected for the purpose of this study: high (HD) and low density (LD) sites. Parallel to the density of ant nests, the density of outstations was also higher at the HD site, while the size of outstations and the number of ants residing in them did not differ significantly between the two sites. Outstations were usually maintained by a single ant nest at the LD site, thus the common exploitation of food resources was less frequent, whereas at the HD site outstations were used by more ant nests. This article provides the first evidence to shared use of outstations in E exsecta. In the view of our results outstations, in addition to guarding aphid colonies, also function as permanent meeting points for workers from different nests, which contribute essentially to the integration of nests within a polydomous system.