How Spiders Stick or Not Stick to their Web
Spiders use their sticky webs to catch their food. So why do they not stick? Researchers at the Smithsonian Tropical Research Institute and University of Costa Rica studying why spiders do not stick to their own sticky webs have discovered that a spider’s legs are protected by a covering of branching hairs and by a non-stick chemical coating. Their results are published online in the journal, Naturwissenschaften. They also observed that spiders carefully move their legs in ways that minimize adhesive forces as they push against their sticky silk lines hundreds to thousands of times during the construction of each orb.
A spider web, spiderweb, spider's web or cobweb is a device built by a spider out of spider silk extruded from its spinnerets. Spider webs have existed for at least 140 million years, as witnessed in a rare find of Early Cretaceous amber from Sussex, southern England.
Insects can get trapped in spider webs, providing nutrition to the spider; however, not all spiders build webs to catch prey, and some do not build webs at all. The main difference between spider webs and cobwebs is that spider webs are still in use, while cobwebs are webs that have been abandoned.
The web-weaving behavior of two tropical species, Nephila clavipes and Gasteracantha cancriformis, was recorded with a video camera equipped with close-up lenses. Another video camera coupled with a dissecting microscope helped to determine that individual droplets of sticky glue slide along the leg’s bristly hair, and to estimate the forces of adhesion to the web. By washing spider legs with hexane and water, they showed that spiders’ legs adhered more tenaciously when the non-stick coating was removed.
It was also discovered that during web construction, spiders reduce adhesive forces by strategically moving their legs along the web. With the use of video cameras, hundreds of thousands of leg movements were captured and analyzed.
Spiders do not usually adhere to their own webs, because they are able to spin both sticky and non-sticky types of silk, and are careful to travel across only less sticky portions of the web. However, they are not immune to their own glue. Some of the strands of the web are sticky, and others are not.
Photo: C. Frank Starmer