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Silkworm

Silkworm, common name for the silk-producing larvae of any of several species of moths. Silkworms possess a pair of specially modified salivary glands called silk glands, or sericteries, which are used in the production of cocoons. The silk glands secrete a clear, viscous fluid that is forced through openings, called spinnerets, on the mouthparts of the larva; the fluid hardens as it comes into contact with air. The diameter of the spinneret determines the thickness of the silk thread produced.

The best-known silkworm is the larvae of the common, domesticated silkworm moth. This moth, native to China, was introduced into Europe and western Asia in the 6th century AD and into North America in the 18th century. The moth has been cultivated for many centuries and is no longer known in the wild state. Breeders have produced many varieties of the moth, the most important of which produce three broods of young annually.

A typical adult silkworm moth is yellow or yellowish-white, with a thick, hairy body, and has a wingspread of about 3.8 cm (about 1.5 in). The adult has rudimentary mouthparts and does not eat during the short period of its mature existence; the female dies almost immediately after depositing the eggs, and the male lives only a short time thereafter. The female deposits 300 to 400 bluish eggs at a time; the eggs are fastened to a flat surface by a gummy substance secreted by the female. The larvae, which hatch in about ten days, are about 0.6 cm (about 0.25 in) long. The larvae feed on leaves of white mulberry, Osage orange, or lettuce. Silkworm caterpillars that are fed mulberry leaves produce the finest quality silk. Mature larvae are about 7.5 cm (about 3 in) long and yellowish-gray or dark gray in color.

About six weeks after hatching, the common silkworm stops eating and spins its cocoon. The length of the individual fiber composing the cocoon varies from 300 to 900 m (1000 to 3000 ft). The silkworm pupates for about two weeks; if allowed to complete its pupation period, it emerges as an adult moth. Tearing during emergence damages the silken cocoon beyond commercial use. Therefore, in the commercial production of silk, only enough adult moths are allowed to emerge to ensure continuation of the species. Most of the silkworms are killed by heat, either by immersion in boiling water or by drying in ovens.

Other moths known as silkworm moths include the giant silkworm moths. The larvae of these large moths also spin silken cocoons, but they are less widely used for commercial silk production.

Scientific classification: Silkworms belong to the order Lepidoptera. The domesticated silkworm moth makes up the family Bombycidae and is classified as Bombyx mori. The giant silkworm moths make up the family Saturniidae.
 

 
 
 
 
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"Silkworm," Microsoft® Encarta® Online Encyclopedia 2007
http://encarta.msn.com © 1997-2007 Microsoft Corporation. All Rights Reserved.