Eileen Thompson, age 13, of thristiana Lake, B.C., Canada, for her question:
WHERE DO WE GET SILK?
The Chinese started weaving silk cloth about 2700 B.C. For more than 3,000 years they didn't pass on the secret to other people. The silk trade was very profitable during China's early years. Camel caravans went across Asia, transporting silk from China to Damascus, the marketplace where East and West met.
Silk is an extremely strong, shiny, threadlike substance that is used for making cloth. Its natural beauty isn't found in many fibers. And the beautiful material comes from the cocoons of caterpillars called silkworms.
Silk is actually the strongest of all natural fibers. A thread of silk is even stronger than the same size thread of some kinds of steel. And the thread is very elastic, too.
Cultivated silk is spun by silkworms raised on special silk farms. The raw silk comes chiefly from Japan with China ranking second. Other top silk producers are South Korea, Russia, India, North Korea and Brazil. The United States is the world's leading manufacturer of silk products.
The caterpillar used on the silk farm is produced by a moth called Bombyx mori. The last half of the name comes from the mulberry tree, on which it feeds.
The Bombyx mori in flight is about two inches long. Each summer one female will lay between 300 and 500 eggs which are deposited on special strips of paper provided by the silk farmer. The eggs are put into cold storage until early spring when they are put into incubators. In about 20 days the eggs will hatch into tiny silkworms.
The Young Silkworms have large appetites and eat almost continually night and day. Every two or three hours the farmer provides fresh mulberry leaves. After four or five weeks, during which time they grow about 70 times their original size and shed their skins four times, they are about three inches long and nearly one inch thick.
When fully grown, the silkworm stops eating and spins a cocoon. He does this by swinging his head from side to side in a series of figure eight movements. Two glands near his lower jaw give off a fluid that hardened into fine si_.~ thread as soon as it hits the air. If allowed to develop into a moth, the creature would burst his cocoon and also the continuous thread of silk which encases him. Therefore, the cocoons are placed in a hot oven to kill the insect.
Silkworkers then reel long, delicate threads from the cocoons. Threads from several cocoons are unwound at the same time, because a single slender thread would be too fine to reel.
Later the silk is taken from the reel and twisted into skeins. Fifteen double skeins or 30 small ones are bound into a larger bundle called a book. A bale of raw silk ready to be shipped to a mill for weaving contains about 30 books and weighs about 135 pounds.