Silk is made by the silkworm.

Silkworms aren't really worms at all, but caterpillars. Like other caterpillars, a silkworm spins a cocoon for shelter while it changes into a moth. Silkworms produce the silk thread from specialized silk glands. The entire cocoon is made from one single, unbroken thread.

The thread of a single cocoon can be over 3000 ft long, and it takes 3000 cocoons to make a pound of silk cloth. The Chinese learned to cultivate silk worms and make silk clothing over 5000 years ago. The caterpillars must be fed only leaves from the mulberry tree to survive. After the cocoons are spun, they are boiled in water. As the cocoon loosens, the end of the thread is found and the silk gently pulled from the water.

Today silkworms only occur in captivity, and the adults have lost their ability to fly or survive in the wild.