What are spider webs made of?

CorrespondentOctober 31, 2011 

David Stephan is an insect identification specialist at the N.C. State Plant Disease and Insect Clinic. Here he explains all you ever wanted to know about spider webs. Questions and answers have been edited.

Q: What are spider webs made of?

Spider webs are made of silk, produced from spinnerets at the end of a spider's abdomen. Most spiders have three pairs of spinnerets, which are supplied by silk glands within the abdomen.

A spider may be able to produce as many as six different types of silk. These silks can be used and combined to spin webs, wrap prey, line their retreats, construct egg cocoons and travel.

This silk has some amazing properties. It is composed of a mixture of protein crystals in a matrix of amino acids. This structure makes it one of the strongest of natural fibers, about half as strong as steel. But unlike steel, spider silk is very extensible, so it actually is "tougher" than steel. Researchers are focusing on ways to biosynthesize silk to create new fiber products.

Q: Why are there so many spider webs around this time of year?

This is the season when many spider species are maturing, especially some that construct large, exposed webs. Many spiders overwinter as eggs in cocoons, or as newly hatched babies. They feed and grow throughout the spring and summer and are adults by fall. The smaller webs they spin as juveniles may be hidden in vegetation, whereas adults' larger webs are out in the open.

Q: Why do different kinds of spiders make different kinds of webs?

Species spin different kinds of webs, adapted to their habitats, hunting styles and prey. Spiders can be very flexible about the dimensions and outer shapes of their webs so that they fit the space the spider has chosen; but the internal geometry of the web usually is fairly consistent for each species.

When building a web, a spider probably measures using a combination of available anchoring sites for the threads, leg span distance between threads and tension on threads within the webs. Spiders rely greatly on their sense of touch to guide them in web building. They don't have to learn this; it's all done by instinct.

But not all spiders use their silk to spin webs for prey capture. Many species are wandering hunters that ambush, stalk or run down their prey.

Q: How do spiders not get stuck in their own webs?

A web may be composed of sticky and non-sticky silk threads. When moving around its web, a spider may use only the non-sticky threads as footholds. It's careful to avoid contacting the web with its body, using only the claws at the tips of its legs to grasp the threads. In case of an accident, an oily coating on its body and hairs keep it from becoming stuck like its prey.

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