Prey attraction as a possible function of the silk decoration of the uloborid spider Octonoba sybotides

Abstract

Both laboratory experiments and field observations were used to examine the prey-attraction hypothesis for the function of the silk decoration on the orb web of Octonoba sybotides. The reflectance spectrum of the decorative silk showed that the decorations reflect relatively more ultraviolet (UV) light. Choice experiments were conducted using Drosophila melanogaster, a common prey species of the spider, to determine whether webs with silk decoration attract more flies than undecorated webs. The choice experiment showed that webs with silk decoration attract more flies in light that includes UV rays. However, flies choose their flight direction randomly in light without UV rays. This suggests that the silk decoration might attract prey insects that tend to fly toward UV-reflecting objects. Field observations comparing the prey capture rate between webs with and without a silk decoration showed that more prey are caught in decorated webs. In this study, no difference between the two forms of silk decoration, linear and spiral, was detected either in prey attraction in the choice experiment or in the prey capture rate in the field observations. Key words: choice experiment, Octonoba sybotides, prey attraction, prey capture rate, silk decoration, ultraviolet light. [Behav Ecol 10:607‐611 (1999)]