Conservation status: Domesticated
The silkworm (Bombyx mori, Latin: "silkworm of the mulberry tree") is the larva or caterpillar of a moth that is very important economically as the producer of silk. A silkworm's diet consists solely of mulberry leaves. It is native to northern China and Persia (current Iran).
Silkworms have a strong appetite, as do all lepidopteran larvae. They eat mulberry leaves day and night. Thus, they grow very fast. When the colour of their heads turns darker, it means that it is time for them to moult. After they moult about four times, their bodies turn slightly yellow and their skin becomes tighter, which means they are going to enter an apparently resting state (the pupa or chrysalis), during which they transform themselves into moths. Before becoming a pupa, the silkworm encloses itself in a cocoon, for protection during the vulnerable, almost motionless pupal state. The silkworm is so called because it spins its cocoon from raw silk produced in its salivary glands.
The cocoon is made of a single continuous thread of raw silk from 300 to 900 meters (1000 to 3000 feet) long. The fibers are very fine and lustrous, about 1/2500th of an inch in diameter. About 2,000 to 3,000 cocoons are required to make a pound of silk. Based on 2/3 of mile (1 km) per cocoon, ten unraveled cocoons could theoretically extend vertically to the height of Mt Everest. It is estimated that at least 70 million pounds of raw silk are produced each year, requiring nearly 10 billion pounds of mulberry leaves. According to E. L. Palmer (Fieldbook of Natural History, 1949), one pound of silk represents about 1,000 miles of filament. The annual world production represents 70 billion miles of silk filament, a distance well over 300 round trips to the sun!
If the caterpillar is left to eat a hole on the cocoon, in order to exit as a moth, the threads will be cut short and the silk will be useless, so silkworm cocoons are thrown into boiling water, which kills the silkworms and also makes the cocoons easier to unravel. The silkworm itself is often eaten.
The adult phase (the moth) has been bred for silk production and cannot fly. It is also called the silkworm-moth. They have a wingspan of 2 inches and a white hairy body. Because of its long history and economic importance, the silkworm genome has been the object of considerable study recently.
One of the silkworm's deadliest enemies are ants, who devour the silkworms. But be careful not to confuse young, tiny silkworms with ants, as they look somewhat alike. Silkworms suffer from infectious diseases caused by protozoans, fungi, viruses, and bacteria. The French microbiologist Louis Pasteur investigated several silkworm diseases, which threatened the European silk production at that time.
In China, there is a legend that the discovery of the silkworm's silk was by an ancient empress called Xi Ling-Shi ( Chinese: 嫘祖; Hanyu Pinyin: Léi Zǔ). She was walking around when she noticed the worms. Touching it with her fingers, a strand of silk came out. As more came out and wrapped around her finger, she slowly felt a warm sensation. When the silk ran out, she saw a small cocoon. In an instant, she realized that this cocoon was the source of the silk. She taught this to the people and it became widespread. There are many more legends about the silkworm.
The Chinese jealously guarded their knowledge of silk. It is said that a Chinese princess smuggled eggs to Japan, hidden in her hair. The Japanese thus began their love affair with silk. It takes 2100 silk worms to make a single kimono.
Silkworm is the source of the traditional Chinese medicine "bombyx batryticatus" or "stiff silkworm" ( Simplified Chinese: 僵蚕; Traditional Chinese: 僵蠶; Hanyu pinyin: jiāngcán). It is the dried body of the 4–5th stage larva which has died of the white muscardine disease caused by the infection of the fungus Beauveria bassiana. Its uses are to dispel wind, dissolve phlegm and relieve spasm.
In Korea silkworm pupae, boiled and seasoned, are a popular snack food.