Nature – Why Don’t They Get Stuck?

Flies and moths unwittingly find themselves trapped in a spider’s web, hopelessly entangled and unable to free themselves. But the spider can rush across the web to enjoy a tasty, fresh meal without being trapped itself. A study published by two Costa Rican biologists some years ago suggests that spiders stay unstuck thanks to a combination of behavior, anatomy and, yes, even an oily non-stick coating.

Webs typically look something like a wheel with a series of spirals that form the round shape connected by spokes running from the outside spiral to the center of the web. It appears that the spiral strands are coated with droplets of adhesive. When a bug flies into a spider’s web it is instantly stuck, or if you walk into a web, the strands stick to your skin, hair, and clothing. Uck!

Spiders avoid getting stuck by walking on the spoke strands which do not have adhesive on them. If by chance the spider should stray into a sticky area, it will very gently pull the trapped leg back. The key word being gently. Pulling quickly or jerkily, like a bug trying to avoid becoming a main course, causes the adhesive to harden and trap the body.

In addition, the spider has oily substances and special hairs on its legs that prevent it from getting stuck, and it tiptoes carefully from strand to strand.

A spider is also a very careful groomer. It pulls each of its legs through its mouth scraping off any silk bits and other debris that may have gotten stuck to its claws or bristles. This grooming likely ensures that its legs and body are less prone to sticking if it should suffer a misstep in the web.