Raw silk thread, called a “filament,” is drawn from the cocoons of several moth species. The caterpillars that spin the cocoons are commonly called “silkworms.”
Silk production involves growing mulberry trees to provide food for the silkworms, which eat more than fifty thousand times their weight in mulberry leaves. It also involves caring for the silkworm as an egg, a caterpillar, and as a chrysalis within a cocoon. The chrysalis is the final stage before the silkworm emerges as an adult moth.
The female moth lays hundreds of eggs, each about the size of a pinhead, before dying almost immediately after. The eggs are stored through the winter and allowed to hatch only the following spring.
About four to six weeks after hatching, the caterpillars reach maximum size and begin to spin their cocoons. This takes about four days. Glands on the caterpillar’s head secrete a liquid that becomes the silk filament. Each cocoon is made of a single filament, two to three thousand feet long.
In order to kill the chrysalises, the finished cocoons are either steamed, put in jars layered with salt, or boiled. The caterpillars have to be prevented from becoming full-grown moths in order to preserve the cocoon and its thread. The only moths allowed to live are those selected as breeding stock for future generations of silkworms.
Each cocoon is made of a single filament two or three thousand feet long. This is called “floss,” which is twisted to make silk thread.
Although the Chinese used other raw materials such as hemp to make cloth, silk was the most useful and valued fabric for many centuries. It was only with the spread of cotton production in the fourteenth and fifteenth centuries that silk was eclipsed as a fabric for daily use.