The ability of insects to see and avoid webs is an important factor affecting the foraging success of orb-spinning spiders. Web visibility results from the relative contrast between webs and their backgrounds. Here I manipulate web and background contrast to explore their affect on insect encounter with spider webs. In three different light environments, insects intercepted webs suspended in front of white and black backgrounds with equal frequency. However, when the reflective properties of webs were experimentally enhanced, insects were able to see and avoid them. Because web stickiness and brightness are a function of the viscid material that coats the web spiral thread, the data suggest an interdependence between insect retention in webs and their visibility. Spiders occupying nocturnal or dim, diurnal sites may not be constrained by the reflective properties of viscid silks and thus able to capture prey that can only be retained by extremely sticky, and hence reflective, webs. These spiders may make use of alternative resources and evolutionary opportunities not available to spiders foraging in bright, visual environments.
