Daily and seasonal changes in the stickiness of viscous capture threads in Argiope aurantia and Argiope trifasciata orb-webs.

The spirally arrayed viscous capture threads of spider orb-webs are formed of small, regularly spaced adhesive droplets and are responsible for retaining insects that strike the web, giving a spider more time to subdue these prey. These sticky threads are deposited from the perimeter of the web inward. We tested the hypothesis that depletion of silk reserves during web construction affects the properties of capture threads spun by adult female Argiope aurantia and Argiope trifasciata. In both species the droplet volume (DV) per millimeter thread length was the same in outer and inner capture threads and in early and late season webs. However, the outer threads of both species were stickier than their inner threads and, consequently, had a greater stickiness per DV. Thus, dwindling silk reserves during web construction appeared to reduce the stickiness of both species' threads by changing the composition rather than the volume of their viscous droplets. In A. trifasciata, which we studied later in the fall than A. aurantia, there were also seasonal declines in both thread stickiness and stickiness per DV, which may result from either the depletion of silk reserves or the reallocation of these resources. Early season webs of A. trifasciata also had greater stickiness per square centimeter of capture area than late season webs, better equipping these early webs to retain insects.