THE silk of spiders first evolved 400 million years ago and orb webs emerged 180 million years ago(1,2); present-day spiders’ webs are structures efficiently engineered by nature. The planar orb web of the garden spider Araneus diadematus has evolved with the prime function of capturing fast-moving and, on a relative scale, massive insects. We have now analysed the structural engineering of a complete web, using computer modelling, to incorporate the measured time-dependent stress-strain characteristics of the two chief types of web silk. With this model we unexpectedly discovered that aerodynamic damping plays a crucial role in prey capture, an observation that we confirmed in laboratory experiments on real webs.