Deceptions of light and shadow: do the visual cues of Gasteracantha cancriformis (Araneae, Araneidae) improve prey interception by webs in the forest understory?

Abstract

Body coloration of orb-web spiders was previously hypothesized to be attractive to insects, luring potential prey, or associated with protection against visually oriented predators. We combined manipulative experiments with spectral reflectance analyses to test the prey attraction hypothesis, using the araneid spider Gasteracantha cancriformis as a model. The study was conducted in a shaded environment, within a forest fragment of the Atlantic forest located in Southeastern Brazil. Insect interception on web surfaces displaying the dorsal section of G. cancriformis opisthosoma, which emits blue fluorescence and reflects light in the ultraviolet wavelength region, was higher than on surfaces displaying the spider's ventral section, or in webs without spiders. This study supports the prey attraction hypothesis by providing evidence that the color patterns of G. cancriformis dorsum improve prey interception by their webs. Fluorescence and achromatic cues are probably important to lure and attract potential prey.