The influence of group size on dispersal in the social spider Stegodyphus mimosarum (Araneae, Eresidae)

The costs and benefits of group living vary with group size, and competitio n for resources increases with increasing group size. In the social spider, Stegodyphus mimosarum, individuals attain smaller sizes, and survival is l ower in larger colonies. In this study we assess whether group size influen ces the decision to leave a colony-or disperse. Four colony sizes (8, 16, 3 2 and 64) of S. mimosarum were set up under a proportional feeding regime i n a laboratory experiment. We expected more spiders to leave large colonies due to intra-group competition. However, there was no significant increase in the number of spiders leaving with increasing group size. Significantly more spiders left a colony during spring and when spiders were larger (at a more advanced stage of development). Variability in access to resources d oes not promote dispersal, but season and spider sire does influence disper sal.