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 competition for resources increases with increasing group size. In the social spider, Stegodyphus mimosarum, individuals attain smaller sizes, and survival is lower in larger colonies. In this study we assess whether group size influences the decision to leave a colony-or disperse. Four colony sizes (8, 16, 32 and 64) of S. mimosarum were set up under a proportional feeding regime in 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 does not promote dispersal, but season and spider sire does influence dispersal.