The cocoon is made of one thread of raw silk from 300 to 900 meters (1000 to 3000 feet) long. The fibers are very thin. About 2,000 to 5,000 cocoons are needed to make a pound of silk.
If the animal is allowed to survive after spinning its cocoon, it will make a hole in the cocoon when it exits as a moth. This would cut the threads and ruin the silk. Instead, silkworm cocoons are thrown into boiling water, which kills the silkworms and also makes the cocoons easier to unravel. Often, the silkworm itself is eaten.
The adult silkworms (moths) cannot fly. The silkworm-moths have wings about 2 inches wide and a white hairy body. Females are about two to three times bigger than the males, but similarly colored. Adult silkworms have small mouths and do not eat.