Supercontraction stress in spider webs.

Silk produced from the major ampullate (MA) gland supercontracts when wet, and in this paper, we investigate the consequences of high humidity and of the added load of water droplets condensing from saturated air on the mechanical integrity of the spiders' orb web. We measured the development of the supercontraction stress (sigma(sc)) with time when fixed lengths of MA silk from Nephila clavipes and Argiope aurantia were exposed to increasing humidity. Supercontraction generated stresses of about 50 MPa, and extension of these samples to stresses between 150 and 1100 MPa show a time dependent relaxation over 1000 s to approximately 75% of the initial tension but show no indication of failure. We conclude that supercontraction can maintain tension in webs and does not limit the ability of the web to support loads in excess of the supercontraction stress.