7/16/97 - How does a spider web work?

How does a spider web work?

(Lansing State Journal, July 16, 1997)


As the number of insects increases during the warmer months, so does the number of their predators. Spiders are members of the arachnid family which also includes animals such as ticks, scorpions and mites. There are at least 40,000 different kinds of spiders. Not all spiders spin webs, but most of them do. Their webs are made out of silk which originates from special glands in the spider's abdomen. The only manmade material which even comes close to being as strong as spider silk is steel. In fact, for an equivalent weight, the strongest spider silk has a tensile strength that is five times greater than steel. Tensile strength is the amount of longitudinal stress that a substance can tolerate without being torn apart (a measure of how hard can you pull on a string before it breaks).

Spider webs can take a variety of forms, but the most common type is the orb web. An orb web has several spokes that lead outward from a common origin. The number of spokes contained in a web varies with the species of spider spinning it. These spokes are then connected by spirals of spider silk. As the spider spins the web it uses a type of silk thread known as "dry thread." Once the "dry spiral" web is completed the spider then lays down a sticky spiral of thread and eats the dry one. This sticky spiral web must be replaced every few days because it loses its "stickiness."

The pattern and complexity of orb webs varies from species to species and some scientists have suggested that the very pattern of the spider web is designed to attract insects. These webs are thought to produce patterns that resemble patterns reflected by many flowers in UV light. Thus insects who are searching for their favorite type of flower see the decorated web in the UV light and fly into the trap.



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