Silkworm larva and cocoon.
The silkworm is the caterpillar of a moth, Bombyx mori, which, like many other caterpillars, spins itself a cocoon of silk in which it pupates. The cocoon of B. mori is, however, especially thick and may be composed of a single thread commonly 900 meters (2,950 feet) long. This is unraveled to provide commercial silk. Originally a native of China, B.mori has been introduced to many countries. The caterpillar, which takes about a month to develop, feeds on the leaves of the mulberry tree.