Albuquerque, New Mexico-- Need a strong elastic fiber? Try black widow silk. The thread spun by these deadly spiders is several times as strong as any other known spider silk--making it about as durable as Kevlar, a synthetic fiber used in bulletproof vests, according to a report presented here at the annual meeting of the Society for Integrative and Comparative Biology.

For several years, materials scientists and biologists have been studying the silk spun by orb spiders, such as the common garden spider Araneus diadematus, because the draglines that frame their flat, circular webs stretch without breaking and could be the basis for new synthetic fibers. But biologist Anne Moore of Scripps College in Claremont, California, is the first researcher to study silk used in cobwebs--three-dimensional, tangled networks of silk. She found that in some respects these strands are superior to those spun by orb spiders.

The black widow's cobweb consists of support scaffolding--a region in the middle for catching prey--and a series of silk anchor lines that hang down and snag walking insects. Moore cut pieces of the scaffold silk from the webs of five spiders and mounted each on a piece of cardboard with a slit in it. Next, she measured the amount of force needed to break the threads. Moore found that the black widow uses two kinds of silk for scaffolding. One can stretch an extra 25% of its length before breaking and is twice as strong as the orb spider's dragline. The other is even stronger than the first but slightly less elastic.

"It's astounding that the [black widow] silk has a combination of that strength and that extension," says spider-silk researcher John Gosline from the University of British Columbia in Vancouver, who says it's "very remarkable" that black widow silk is stronger than orb spider draglines.