The Influence of Starvation on Dispersal in the Social Spider, Stegodyphus Mimosarum (Araneae, Eresidae)

Colonies of the social spider, Stegodyphus mimosarum, are philopatric and inbred, with limited dispersal capabilities. Colony founding events by mature males and females have been observed periodically. We set out to test the influence of food on the spiders' readiness to leave a colony. Thirty colonies (40 spiders in each) were established under laboratory conditions and confined within netting. For 31 days, 15 colonies were fed daily ad libitum, so that the mean amount of food available was greater than the mean requirements of the colony. The other fifteen colonies were starved. The netting was then removed, permitting emigration and movement from colonies was noted for two weeks. Following risk sensitivity theory, we expected more spiders to leave the unfed colonies due to starvation. However, a significantly higher absolute number of spiders left colonies where food was abundant. While fewer spiders left unfed colonies, more of these spiders died, such that the relative number of spiders remaining at the end of the trial was not significantly different between treatments. Even when they were starved, the decision to leave a colony was not based on a lack of food. Low food availability increased mortality, yet it did not alter the remaining spiders' decision to move. Therefore the decision to move is based on factors beyond prey availability, which may include the state of maturity of the spiders, the motivational state, the high cost of migration and reserves.