The silk is obtained from the cocoon made by the "worm". It's claimed the worms are a good source of protein if an astronaut can't get Kellogg's Special K cereal and milk delivered to the space station.
The best-known type of silk is obtained from cocoons made by the larvae of the mulberry silkworm Bombyx mori reared in captivity (sericulture)
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Commercially reared silkworm pupae are killed by dipping them in boiling water before the adult moths emerge, or by piercing them with a needle, allowing the whole cocoon to be unraveled as one continuous thread