Ultraviolet is a more important cue than reflection in other wavelengths for a jumping spider to locate its spider prey

Many orb-web spiders put silken decorations that reflect ultraviolet (UV: <400 nm) light in their web. The function of web decorations has been extensively studied: they may increase foraging success or reduce predation risk, but can also be a liability for the web-building spiders. Earlier studies have shown that the reflectance of silken decorations in UV helps an araneophagic jumping spider, Portia labiata, locate and prey on a web-decorating spider, Argiope versicolor. However, it is unclear whether the reflectance of silken decorations in UV is more important as a cue than reflectance in other wavelengths (400–700 nm) for P. labiata to locate the web-building spiders. We investigated the relative importance of reflection of web decorations at different wavelengths in assisting P. labiata in locating its prey, A. versicolor. Portia labiata was given a choice of four webs with cruciform silk decorations built by A. versicolor, the appearance of which was manipulated using coloured filters that selectively blocked UV, short-wavelength (SW: 400–500 nm), medium-wavelength (MW: 500–600 nm) and long-wavelength light (LW: 600–700 nm). Significantly fewer P. labiata preferentially approached the decorated webs from which the reflectance in UV was blocked than webs from which the reflectance in SW, MW and LW was blocked. These results suggest that the reflectance of decorations in UV is a more important visual cue than short, medium and long wavelengths for P. labiata to locate the decorated webs.

► We blocked reflections from Argiope versicolor web decorations at different wavelengths.
► Only blocking UV reflections reduced number of Portia approaching webs.
► Thus UV is more important than other wavelengths for Portia to locate Argiope.