Silkworm

Silkworm, common name for the silk-producing larvae of any of several species of silkmoths. 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 common domesticated silk moth, native to China, was introduced into Europe and western Asia in the 6th century ad. 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 silk moth is yellow or yellowish-white, with a thick, hairy body, and has a wingspan of about 3.8 cm (1y in), although it is unable to fly. 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 afterwards. 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 (‚ in) long. The larvae feed on leaves of mulberry, Osage orange, or lettuce. Silkworm caterpillars that are fed white mulberry leaves produce the finest quality silk. Mature larvae are about 7.5 cm (3 in) long and yellowish-grey or dark grey in colour.

About six weeks after hatching, the common silkworm stops eating and spins its cocoon. The length of the individual fibre composing the cocoon varies from 300 to 900 m (1,000 to 3,000 ft). The silkworm pupates for about two weeks; if allowed to complete its pupation period, it emerges as an adult moth. Tears made by the moth as it emerges damage 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 silk moths include the giant silk 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 silk moth belongs to the family Bombycidae and is classified as Bombyx mori. The giant silk moths belong to the family Saturniidae.