Why spiders don’t stick to their own web

If you walk into a spider’s web, you generally get it stuck all over you, but spiders don’t stick to their own webs and researchers in America think they know why.

Previous research suggested that spiders didn’t stick to their own webs because of an oily coating that protects against adhesion. Later research suggests that spiders actually just avoid the sticky lines, but this explanation is inadequate because orb-weaving spiders push their hind legs against sticky lines hundreds or thousands of times during web construction.

To solve the problem, researchers from the Smithsonian Tropical Research Institute and University of Costa Rica repeated the research using modern techniques. They recorded the web-weaving activities of two tropical spider species – Nephila clavipes and Gasteracantha cancriformis – with a video camera with a close-up lens. Another camera coupled with a dissecting microscope.

“Video analyses of behaviour and experimental observations of isolated legs pulling away from contact with sticky lines showed that the spider uses three anti-adhesion traits: dense arrays of branched setae on the legs that reduce the area of contact with adhesive material; careful engagement and withdrawal movements of its legs that minimize contact with the adhesive and that avoid pulling against the line itself; and a chemical coating or surface layer that reduces adhesion,” said the research, published in Naturwissenschaften.

Spider’s legs are protected by a covering of branching hairs and a non-stick chemical coating which ensures individual droplets of sticky glue slide along the leg’s bristly. The spider’s legs were washed with hexane and water to show that the spiders’ legs adhered more tenaciously when the non-stick coating was removed.

The two videos below illustrate how the Gasteracantha spins its web and the bristly legs of the Nephila.

In the first, researchers slowed down video images in order to carefully observe how a spider (Gasteracantha) handles the sticky silk that it uses to trap its prey, pulling the silk out of its abdomen with its fourth leg and stretching it to weave its web.

http://www.youtube.com/watch?v=FtDAo9GQ-eo

In the second, Nephila clavipes is building a web: you can clearly see the pointed drip tip of the bristly hairs on the spider's leg – any adhesive from the web that sticks to the spider's leg readily drips off.

http://www.youtube.com/watch?v=TL8_MREXstk

• Spiders avoid sticking to their webs: clever leg movements, branched drip-tip setae, and anti-adhesive surfaces