Viscoelastic solids explain spider web stickiness

Modern orb-weaving spiders have evolved well-designed adhesives to capture preys. This adhesive is laid on a pair of axial silk fibres as micron-sized glue droplets that are composed of an aqueous coat of salts surrounding nodules made of glycoproteins. In this study, we measure the adhesive forces required to separate a small microscopic probe after bringing it in contact with a single glue droplet. These forces are highly rate-dependent and are two orders of magnitude higher than the capillary forces. The glycoproteins in the glue droplets behave as a viscoelastic solid and the elasticity is critical in enhancing adhesion caused by specific adhesive ligands. These results have important implications in mimicking bioadhesives. Spider silk adhesion is reliant on sticky droplets composed of glycoproteins surrounded by an aqueous coat. Sahni and co-workers show that these droplets behave as viscoelastic solids that enable large, rate-dependent adhesive forces capable of trapping fast- and slow-moving prey.