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Mark Wewer, age 13, of Little Rock, Ark., for his question:

HOW DOES A SILKWORM SPIN SILK?

Legend says that silk was discovered about 2700 B.C. when the emperor ordered his wife to find out what was damaging his mulberry trees. She found white worms eating the leaves and then spinning themselves into cocoons. She dropped one of the cocoons into hot water by accident and then discovered silk when she found that the cocoon was made up of slender threads.

No one knows exactly who discovered silk, but historians tell us that silk making was a guarded Chinese secret for about 3,000 years. Beautiful silk material was strictly a Chinese trade item until the Byzantine emperor Justinian tired of paying high prices for silk in about 550 A.D. He sent two spies to China and they smuggled out silkworm eggs and mulberry seeds in hollow bamboo canes. The monopoly was then broken.

Production of silk requires a great deal of patience and careful work.

Silkworms are raised on silk farms. Today Japan leads the world in production, followed by South Korea, Russia, India, North Korea and Brazil.

The Bombyx mori is a large white female moth with black lined wings who lays from 300 to 500 eggs early each summer. The silk farmer puts the eggs on special strips of paper and then stores them until early the next spring when they are placed in an incubator. After about 20 days at a suitable temperature the eggs hatch into tiny silkworms.

Next the eating game starts. Silkworms eat almost constantly both day and night. Farmers provide them with fresh mulberry leaves every two or three hours and in about a month or five weeks the worms have grown to 70 times their original size and have shed their skins four times. The worm is now fully grown and is about an inch thick and three inches long.

The adult worm is then ready to spin his cocoon. Hanging from a twig and swinging his head from side to side in a series of figure eight movements, the worm releases a fluid from two glands near the lower jaw. The fluid hardens into fine silk threads as soon as it hits the air. For about three days the worm will spin threads which are immediately wrapped around his body  and he changes into a pupa.

Silk farmers allow some of the pupa to continue the life cycle and turn into moths, but most of them are placed in hot ovens to kill the insect. The cocoons are then soaked in tubs of hot water to dissolve the gummy sericin that holds the threads together, and silk threads are then unwound.

When the raw silk leaves the cocoon, it is not strong enough to be woven into anything except perhaps the sheerest of material. It is strengthened by a process called throwing. In this procedure, a number of strands of silk are twisted together. The number depends on the type of fabric that is to be woven.

Silk yarns are woven on looms much like those used for wool and cotton.

 

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