Testing the Functions of Detritus Stabilimenta in Webs of Cyclosa fililineata and Cyclosa morretes (Araneae: Araneidae): Do They Attract Prey or Reduce the Risk of Predation?


Marcelo O. Gonzaga, Departamento de Zoologia, Instituto de Biologia, Unicamp, Caixa Postal 6109, Campinas, SP, Brazil CEP 13083-970. E-mail: mogonzaga@yahoo.com.br


Spiders of the genus Cyclosa often add prey remains and other debris to their orb-webs. The function of silk decorations is generally associated with defense against predators or with the attraction of prey, but few studies have focused on stabilimenta containing detritus. In this study, we used artificial webs with and without the detritus stabilimenta of two species of Cyclosa to investigate whether these structures increase the number of insects intercepted. Artificial models of spiders and stabilimenta were used to compare the frequency of attacks against different shapes. We also conducted choice experiments in laboratory to determine whether detritus columns attracted Drosophila melanogaster (Diptera: Drosophilidae) and Trigona angustula (Hymenoptera: Apidae, Meliponinae) to the webs. The frequency of interception in artificial webs with a stabilimentum was similar to that of webs without such structure. The taxonomic composition and biomass of insects were also similar in both types of artificial webs. The choice experiments showed no significant tendency in attraction to webs with a stabilimentum. However, models of spiders were attacked at a higher frequency than those simulating detritus columns and silk decorations. These findings argue against the prey attraction hypothesis and suggest that the addition of stabilimenta to webs of Cyclosa could reduce the intensity of predation, possibly by disrupting the image of the spider's outline.