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The Mighty Gossamer
| Article
# : |
18462 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
9 / 1990 |
1,718 Words |
| Author
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Fritz Vollrath
Fritz Vollrath is assistant professor of zoology at Basle
University, Switzerland, and research associate in zoology at
Oxford University. |
Four and a half thousand years ago, little Si-Ling-Shi of the southern capital of Hang-Chow-Foo discovered silk. Or so the legend goes. The princess, who later became goddess of the Chinese silk industry, happened to observe a small caterpillar spinning its cocoon. She noticed that the cocoon consisted of a single thread and realized that unraveling the silken structure would yield a thread that, bundled together with many others, could be used to spin the most exquisite of garments. And so they were, of a luster and strength unrivaled until the development of the first man-made polymer plastics, not so long ago.
Soon, silk may have its comeback: Genetic engineers claim to have inserted silk genes into bacteria and are waiting only for the machinery necessary to express this bacterial silk into fibers. However, this new, artificial silk is not modeled on the silk of Bombyx mori, the lepidopteran caterpillar observed by Si-Ling-Shi, but on that of the garden spider, Araneus diadematus, and the gigantic golden orb spider, Nephila clavipes.
Spiderweb silk must be strong enough to halt an insect in midair; it must be thin to minimize the spider's expenditure of protein; and it must be of even diameter throughout, as otherwise the entire thread will break. However, a spider produces more than one kind of silk, and not all of them are used in her web. One sort functions like silkworm fibers, providing the tough covering of the little sac that contains the spider's eggs. Another silk has a double function; fluffed up, it cradles the delicate eggs, but when paid out in ribbons it entangles and enshrouds the unfortunate prey insect. Being a shrewd economist, the spider actually puts most of its silk to double duty: The safety line, trailed
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