silk

silk A material produced by the silk glands of spiders, some insects, and certain other invertebrates (e.g. centipedes). It is exuded as a liquid by a protruding appendage, the spinneret, but quickly hardens after leaving the gland. Silk is composed of α-keratin crystals embedded in a rubbery matrix of amino-acid chains, giving the material its flexibility and strength. A spider typically has several silk glands each producing a different type of silk, with properties determined by the nature of the amino-acid matrix. The spider switches from one gland to another to produce the silk appropriate for the task. For example, the silk used for wrapping prey is softer and distinct from structural silk used for the main fibres of a capture web. The silk may also be coated with a lipid waterproofing layer, as well as fungicides and bactericides to prevent attack from microorganisms.

silk Natural fibre produced by many creatures, notably the silkworm. The many kinds of silk cloth include crépe, satin, taffeta, and velvet. Almost all silk comes from silkworms reared commercially; a single cocoon can provide between 600 and 900m (2000–3000ft) of filament. When the cocoons have been spun, the silk farmer heats them to kill the insects inside. The cocoons are then soaked to unstick the fibres, and the strands from several cocoons are unwound together to form a single thread of yarn. The Chinese were the first to use silk. Silk manufacturing developed in England in the 17th century. China is still the largest producer of raw silk.