Costs and benefits of foraging associated with delayed dispersal in the spider Anelosimus studiosus (Araneae, Theridiidae)

In the theridiid spider, Anelosimus studiosus, most juveniles remain in the ir natal web, forming temporary colonies in which individuals cooperate in web maintenance and prey capture until they disperse at maturity. There is natural variation in age at dispersal, and subadult spiders removed from th eir natal webs build webs and continue to develop. To explore the costs and benefits of delayed dispersal, we compared the rate of prey capture and de velopmental rate for individuals in colonies and those isolated at the four th instar. Rate of prey capture by colonies increased with colony size and age; this result was driven primarily by the enhanced capture of large prey by larger and older colonies. The presence of juveniles increased the over all productivity of webs, an effect which remained after the juveniles were removed from the web. Despite the overall increase in prey capture, per-in dividual prey capture decreased with colony size. The variance in prey capt ure success decreased significantly with colony size, but not with colony a ge. Spiders in colonies captured more prey per juvenile than singletons exp erimentally dispersed at the fourth instar; however, this did not result in increased development rate of colonial juveniles over isolated juveniles. These data suggest that juvenile A. studiosus benefit from delayed dispersa l by acquiring more resources and acquiring them more steadily. The product ivity of webs of females whose juveniles were removed at the fourth instar remained higher than those of similarly aged females who never produced juv eniles. This suggests that delayed dispersal of juveniles enhances the reso urces which the female could allocate to her next egg mass.