Spider’s web

    
(a)                                                                                                                 (b)
Fig. 11-10: Spider’s webs (Courtesy of Dr ASK Kwan, Cardiff University)

Spiders have been able to produce silk for the last 400 million years and have been building orb webs for the last 180 million years. The webs have evolved to arrest the flight and capture fast moving and relatively large insects [11.8, 11.9]. Fig. 11-10 shows two spiders’ webs that consist of radial threads, capture spirals and anchor threads.

The anchor threads span from the supports and suspend the radial threads. The radial threads are then overlaid by the sticky capture spirals. The prestressing is applied during construction by simply pulling the individual strands tighter around their supports.