WEB GLUE RELEASES RATHER THAN BREAKING

The fate of any hapless insect blundering into a spider's web is almost certainly sealed. Ensnared by sticky spirals, most victims can only wait until despatched by the web's occupant. However, some prisoners successfully break free. Brent Opell from Virginia Tech is fascinated by spider webs. He explains that elastic glycoproteins, in the adhesive droplets distributed along the sticky spiral, attach to the web's prisoner and the outermost droplets stretch until eventually letting go rather than damaging the web. But which aspect of the droplet fails? Opell explains that either the drop could break in two, or the glycoprotein adhesive could release from the surface of the captive. Intrigued, Opell and his colleagues Harold Schwend and Stephen Vito measured the stickiness of threads from orb-webs spun by the orchard spider, labyrinth spider and spinney micrathena using materials that have different surface energies (p. 2237). These materials ranged from Teflon, renowned for its non-stick characteristics and low surface energy, to plastic food wrap, whose high surface energy causes it to stick readily to surfaces. Finding that the stickiness of spider threads was directly related to the surface energy of the materials to which they adhered, Opell and his colleagues conclude that instead of breaking in two as force on the droplets increases, the glycoprotein glue within the elongating droplets releases from the surface, saving the web from destruction.