Spider orb webs rely on radial threads to absorb prey kinetic energy

Abstract

The kinetic energy of flying insect prey is a formidable challenge for orb-weaving spiders. These spiders construct two-dimensional, round webs from a combination of stiff, strong radial silk and highly elastic, glue-coated capture spirals. Orb webs must first stop the flight of insect prey and then retain those insects long enough to be subdued by the spiders. Consequently, spider silks rank among the toughest known biomaterials. The large number of silk threads composing a web suggests that aerodynamic dissipation may also play an important role in stopping prey. Here, we quantify energy dissipation in orb webs spun by diverse species of spiders using data derived from high-speed videos of web deformation under prey impact. By integrating video data with material testing of silks, we compare the relative contributions of radial silk, the capture spiral and aerodynamic dissipation. Radial silk dominated energy absorption in all webs, with the potential to account for approximately 100 per cent of the work of stopping prey in larger webs. The most generous estimates for the roles of capture spirals and aerodynamic dissipation show that they rarely contribute more than 30 per cent and 10 per cent of the total work of stopping prey, respectively, and then only for smaller orb webs. The reliance of spider orb webs upon internal energy absorption by radial threads for prey capture suggests that the material properties of the capture spirals are largely unconstrained by the selective pressures of stopping prey and can instead evolve freely in response to alternative functional constraints such as adhering to prey.

Temperature mediates the effect of humidity on the viscoelasticity of glycoprotein glue within the droplets of an orb-weaving spider's prey capture threads

“…This is achieved principally through the energy absorbing toughness of the web's non-sticky radial lines, with viscous threads making only a minor contribution (Sensenig et al, 2012). Consequently, these viscous threads have been largely selected for prey retention (Blackledge and Eliason, 2007).…”

Humidity-mediated changes in an orb spider's glycoprotein adhesive impact prey retention time

“…The web integrates non-adhesive radial and frame threads that absorb and dissipate the kinetic energy of an insect's impact (Sensenig et al, 2012) with spirally arrayed, adhesive prey capture threads (Sahni et al, 2013) that retain the insect until the spider can locate, run to, and begin to subdue it (Chacón and Eberhard, 1980). Thus, material invested in non-adhesive threads increases the size and velocity of insects that a web can successfully stop and material invested in capture thread increases the time a spider has to prevent an insect from escaping.…”

Wet webs work better: Humidity, supercontraction and the performance of spider orb webs

“…Supercontraction in radii tenses up the web at high humidity. Radii also dissipate most of the kinetic energy of prey (Sensenig et al, 2012). Thus, the greatest influence of environmental humidity on energy absorption by webs during prey capture is likely to manifest through changes in the radii.…”