How Spiders Make Their Silk

Thursday, October 01, 1998
Spider silk is stronger than any known natural or synthetic fiber. Scientists would love to know how to mass-produce it. But unlike the silk from silkworms, spider silk will never be harvested directly from the animals. "Silkworm silk is easily harvested from the cocoon," says Fritz Vollrath, an evolutionary zoologist at the University of Aarhus in Denmark. That can't be done with spiders. "They're cannibals," says Vollrath. "You can't keep thousands of them in a little room."

The alternative is artificial production--if researchers could figure out how spiders produce silk. Recently Vollrath discovered an important part of that process. He's found that the spiders' method is remarkably similar to the process used to manufacture industrial fibers such as nylon: spiders harden their silk by acidifying it.

Vollrath studied the garden cross spider, Araneus diadematus. In particular, he examined a duct through which the silk flows before exiting the spider. Before entering the duct, the silk consists of liquid proteins. In the duct specialized cells apparently draw water away from the silk proteins. Hydrogen atoms taken from the water are pumped into another part of the duct, creating an acid bath. When the silk proteins make contact with the acid, they fold and form bridges with one another, hardening the silk.

Vollrath's discovery might help chemists produce spider silk on an industrial scale. Biologists have already cloned several of the genes that code for spider-silk proteins and may soon be able to induce bacteria implanted with such genes to produce raw liquid silk. "Spider silk is stronger and more elastic than Kevlar, and Kevlar is the strongest man-made fiber," he says. But unlike Kevlar--a plastic used to fill bulletproof vests--spider silk is easily recycled. "When you're done with your shirt, you could eat it," he says, "just as the spider eats its own web."
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