A fiber made by animals, silk is the basis of an expensive kind of cloth. Silk scarves and neckties are popular in the United States and other nations. In Asian countries silk is used for loose robes known as kimonos and for long skirts called saris. Silk thread can be used to sew clothing or to close up wounds after surgery.
How silk is made
Silkworms
Insects called silkworms produce silk. Silkworms are not really worms at all. They are caterpillars that spin cocoons for use as a shelter while they change into a moth. Glands within silkworms make a protein material called fibroin. An exit tube in a silkworm's head lets the fibroin out, and air hardens it. Another pair of glands releases a gummy substance that helps keep the cocoon together. Silk industries remove the gummy substance through a process that leaves the silk smooth and semitransparent (somewhat see-through).
In nature, silkworms grow inside the cocoons they create and then break them open to come out as a moth. Silkworms used for industry are killed in the cocoon by steam or hot air so that they will not damage the cocoon.
Most silk used to make clothing and other products comes from the unwound cocoon of the silkworm known by the scientific name Bombyx mori. The practice of raising these silkworms is called sericulture. Because Bombyx mori silkworms eat the leaves of mulberry trees, growing these trees is an important part of sericulture.
Spiders
Some spiders are also known for making silk. They may create webs of silk to catch food. Spider eggs may be wrapped in silk for protection. The fibers created by spiders, however, are very thin. They are not used in making the silk products used by humans.
History
The silk industry began in China thousands of years ago. For many centuries the Chinese traded silk with other countries but would not tell them how the material was made. By the 2nd century BC silk was so important as a trade product between China and Rome that the 4,000-mile (6,400-kilometer) trade route linking the two civilizations was called the Silk Road. The route remained a major path for trade and travel between Asia, the Middle East, and Europe throughout ancient and medieval times. In the 6th century AD silkworms were stolen from China and brought to the city of Constantinople (today known as Istanbul) in eastern Europe. This allowed Europeans to begin producing silk themselves.
Today nylon and other artificial fibers are often used instead of silk. However, some people continue to purchase silk items because of their high quality. The material has good strength, takes dye well, and can absorb moisture better than many other types of fabrics. China, India, Japan, South Korea, Thailand, and Brazil are among the major producers of silk.