Wonder webs: Golden Orb Weaver spider (Nephila clavipes). (Animal Architects).
The secret of the web's strength? A type of super-resilient silk called dragline. The female Orb Weaver produces the silk in her Pyriformes gland, a cluster of cells that secretes silk-building proteins. When she's ready to weave the web's spokes and frame, she uses her legs to draw the airy thread out through a hollow nozzle in her belly called a spinneret (see photo, below). Dragline isn't sticky, so the spider can race back and forth along it to spin the web's trademark spiral. Dragline also serves as the spider's anchor as she rappels down on snagged prey, like flies and bees.
Unlike some spiders that weave a new web every day, a Golden Orb Weaver reuses her handiwork until it falls apart, sometimes not for two years. The silky thread is five times stronger than steel by weight and absorbs the force of an impact three times better than Kevlar, a high-strength human-made material used in bullet-proof vests. And thanks to its high tensile strength, or the ability to resist breaking under the pulling force called tension, a single strand can stretch up to 40 percent longer than its original length and snap back as good as new. No human-made fiber even comes close.
It's no wonder manufacturers are clamoring for spider silk. In the consumer pipeline: high-performance fabrics for athletes and stockings that never run. Think parachute cords, biodegradable (dissolvable) stitches, artificial tendons, and suspension-bridge cables.
A steady supply of spider silk would be worth billions of dollars--but how to produce it? Harvesting silk on spider farms doesn't work because the territorial arthropods--shell-covered animals without backbones--have a nasty tendency to devour their neighbors.
Now, scientists at the biotechnology company Nexia, in partnership with the U.S. Army, are spinning artificial silk modeled after Golden Orb dragline. The first step: extract silkmaking genes, units of hereditary information, from the spiders. Next, implant the genes into goat egg cells. The nanny goats that grow from the eggs secrete dragline silk proteins in their milk. "The young goats pass on the silk-making gene without any help from us," says Nexia president Jeffrey Turner. Nexia is still perfecting the spinning process, but they hope artificial spider silk will soon be snagging customers as fast as the real thing snags bugs.
Did You Know?
* University of Maryland biologist Gail Patricelli has created "fembots" as robotic stand-ins for female bower birds. She controls the robots' movements to learn more about the birds' interaction during courtship.
* A Golden Orb Weaver spider spins a web in about an hour. Without its web, a spider can't trap prey and will starve.
* Rather than build their own nest, dwarf mongooses and monitor lizards sometimes make homes in the chimneys of termite mounds.
Art & Design: Sketch your dream home. What features does it have and why? Using your dream home as an example, list three ways a structure's form impacts its function.
Critical Thinking: Can you think of other creations humans use that were inspired by animals?
* Animal Homes by Barbara Taylor, Dorling Kindersley Limited, 1996. * Homes: Towers, Tunnels, Webs and Hives, Grolier Educational, 2000. * "Say It With Bowers," by J. Albert C. Uy, Natural History, March 2002. p. 76-83.
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|Date:||Sep 13, 2002|
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