Silk

Silk is a natural protein fibre, some forms of which can be woven into textiles. The best-known type of silk is obtained from cocoons made by the larvae of the silkworm Bombyx mori reared in captivity (sericulture). The shimmering appearance for which silk is prized comes from the fibres’ triangular prism-like structure which allows silk cloth to refract incoming light at different angles.

“Wild silks” are produced by caterpillars other than the mulberry silkworm (Bombyx mori). The term “wild” implies that they are not capable of being domesticated and artificially cultivated like Bombyx mori. A variety of wild silks have been known and used in China, India, Vietnam, and Europe from early times, although the scale of production has always been far smaller than that of cultivated silks. Aside from differences in colours and textures, they all differ in one major respect from the domesticated varieties: the cocoons that are gathered in the wild have usually already been damaged by the emerging moth before the cocoons are gathered, and thus the single thread which makes up the cocoon has been torn into shorter lengths. Commercially reared silkworm pupae are killed before the adult moths emerge by dipping them in boiling water or piercing them with a needle, thus allowing the whole cocoon to be unravelled as one continuous thread. This allows a much stronger cloth to be woven from the silk. Wild silks also tend to be more difficult to dye than silk from the cultivated silkworm.

There is some evidence that small quantities of wild silk were already being produced in the Mediterranean area and the Middle East by the time the superior, and stronger, cultivated silk from China began to be imported.

Many different types of silk are produced by a huge variety of different types of insect (other than moth caterpillars), yet none of these have been exploited for commercial purposes, though there is basic research into the structures of such silks, as there is some variation at the molecular level. It is most commonly produced by larvae, and thus largely limited to insects with complete metamorphosis, but in some cases it is produced by adult insects such as webspinners. Silk production is especially common in the Hymenoptera (bees, wasps, and ants), and is sometimes used in nest construction. Other types of arthropod produce silk, most notably various arachnids such as spiders (see spider silk).