Redesigning spider webs: Stickiness, capture area and the evolution of modern orb-webs

An orb-web's ability to capture insects is enhanced by both increased captu re area and increased stickiness per capture area. As spider size limits th e amount of material that an orb-weaver can invest in the sticky prey captu re threads of its web, these two strategies are in conflict. The origin of modern orb-weaving spiders of the large superfamily Araneoidea was associat ed with the origin of adhesive capture threads. These threads achieve their stickiness at a greater material economy than do the primitive cribellar c apture threads found in orb-webs produced by the superfamily Deinopoidea. C onsequently, araneoid orb-weavers have a greater amount of stickiness at th eir disposal. A comparison of orb-webs produced by these sister clades show s that araneoids expend this stickiness in a manner consistent with the hyp othesis that increased stickiness per capture area is favoured over increas ed capture area. Araneoid orb-webs have, relative to spider weight, smaller capture areas than deinopoid orb-webs and, relative to web capture area, g reater total stickinesses than deinopoid orb-webs. The stickiness per captu re area of araneoid orb-webs is greater than that of deinopoid orb-webs and the spacing of capture thread spirals in araneoid orb-webs is equal to or less than that in deinopoid orb-webs. Thus, araneoid orb-webs are better eq uipped than deinopoid orb-webs to retain insects that strike the web. This increases the ability of araneoid spiders to subdue ensnared insects before they escape from the web and may favour the capture of larger prey.