Chapter 24.3, Problem 1HYEW

If you have ever accidentally walked into a spider web, then you know that the strands of the web can be very sticky indeed. And the small insects one sees trapped in spider webs seem to be quite firmly snared. So how does the spider that built the web scuttle so easily across it without getting stuck? One key factor is that the web is not entirely sticky. The web’s scaffolding is made from non-sticky strands, with sticky ones restricted to the capture area. So a moving spider can often simply stay on the non-sticky strands and avoid the sticky ones. But the spider’s distinctive claws also help. These claws, in conjunction with specialized hairs on the tips of its legs, allow a spider leg to grip a single web strand and then release it. A spider moving in this fashion, grasping strands with only the very tips of its legs, will have only a tiny surface area in contact with the web at anyone time. Thus, even if the spider grips a sticky strand with one of its legs, it can easily pull loose, just as you can if you step on a wad of chewing gum. In contrast, an unsuspecting fly that crashes into the web will contact a number of strands with many parts of its body simultaneously and be stuck fast.

Why Spiders Don’t Stick to Their Own Webs?