Function of being colorful in web spiders: attracting prey or camouflaging oneself?

Abstract

Bright body colorations of orb-weaving spiders have been hypothesized to be attractive to insects and thus function to increase foraging success. However, the color signals of these spiders are also considered to be similar to those of the vegetation background, and thus the colorations function to camouflage the spiders. In this study, we evaluated these 2 hypotheses by field experiments and by quantifying the spiders’ visibility to insects. We first compared the insect interception rates of orbs constructed by the orchid spider, Leucauge magnifica, with and without the spider. Orbs with spiders intercepted significantly more insects than orbs without. Such a result supported the prey attraction but not the camouflaging hypothesis. We then tested whether bright body colorations were responsible for L. magnifica’s attractiveness to insects by manipulating the spiders’ color signals with paint. Alteration of color signals significantly reduced L. magnifica’s insect interception and consumption rates, indicating that these spiders’ bright body parts were attractive to insects. Congruent with the finding of field manipulations were the color contrasts of various body parts of these spiders. When viewed against the vegetation background, the green body parts were lower, but the bright parts were significantly higher than the discrimination threshold. Results of this study thus provide direct evidence that bright body colorations of orb weavers function as visual lures to attract insects. Key words: color contrast, Leucauge magnifica, orchid spider, visual ecology.