Robust performance of spider viscid silk on hairy and smooth insect substrates.

Abstract

Spider viscid silk adheres to insects in orb webs and is a smart-adhesive that quickly changes droplet size, viscosity, and adhesiveness in response to atmospheric humidity. Different species of spiders tune water uptake to match the humidity of their foraging environments, achieving a similar universal viscosity that optimizes tradeoffs in spreading versus cohesive bulk energy needed to enhance adhesion. Too much water lowers viscosity so that the glue spreads well, but cohesive failure occurs easily, generating poor adhesion. However, the optimal viscosity model of adhesion is based on experiments using smooth glass. Here we test the hypothesis that a less viscous, over-lubricated glue, which shows poor adhesion on smooth glass, will be stickier on hairy insects because of its greater ability to spread across three-dimensional rough surfaces. We ran adhesion tests of the furrow spider (Larinioides cornutus (Clerck, 1757)) viscid silk on honey bee (Apis mellifera) thorax, with and without hairs, in either high or medium humidity. Our results show that over-lubricated glue increases adhesion on hairy surfaces, performing equally as well as an optimally viscous glue.