What animal's cocoon is harvested to make silk thread?

A silkworm's cocoon is harvested to make silk thread. The best-known silk-producing insect is the domesticated silkworm, Bombyx mori, whose caterpillar feeds mainly on mulberry leaves.

When the caterpillar is ready to transform into a moth, it spins a cocoon from one continuous filament of fibroin, a strong protein coated with sericin, a gummy substance that helps hold the fibers together. A single cocoon can contain a filament roughly hundreds of metres long.

In traditional silk production, cocoons are usually collected before the adult moth emerges. The cocoons are heated or boiled to soften the sericin, allowing workers to unwind and combine the filaments into usable silk thread. If the moth emerges naturally, it breaks the filament, producing shorter fibers and a less continuous thread.

“Silkworm” refers to the larval stage, not a worm in the biological sense. It is actually a caterpillar that develops into a moth. Several wild insects also produce silk, but Bombyx mori is the central species in commercial sericulture.