Eggs take about ten days to hatch. Silkworms have a strong appetite, as do all lepidopteran larvae. They eat day and night, preferring White Mulberry but not being strictly monophagous they also take other species of Morus and some other Moraceae. Hatchlings and second-instar larvae are called kego (??, "hairy silkworm") in Japan, or chawki in India. They are covered with little black hairs. When the color of their heads turns darker, it means that it is time for them to molt. Later instars are white, nude, and have a horn on the back. After they have molted four times (i.e., in the fifth instar), their bodies turn slightly yellow and their skin becomes tighter. The larvae enclose themselves in a cocoon of raw silk produced in the salivary glands that provides protection during the vulnerable, almost motionless pupal state. Many other Lepidoptera produce cocoons, but only a few large Bombycidae and Saturniidae have been exploited for fabric production. Main article: Silk The cocoon is made of a thread of raw silk from 300 to 900 meters (1000 to 3000 feet) long. The fibers are very fine and lustrous, about 10 micrometers (1/2500th of an inch) in diameter. About 2,000 to 3,000 cocoons are required to make a pound of silk. Based on 1 kilometer (about 1100 yards) per cocoon, ten unraveled cocoons could theoretically extend vertically to the height of Mt Everest. 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 animal is allowed to survive after spinning its cocoon, it will release proteolytic enzymes to make a hole in the cocoon so that it can emerge as a moth. This would cut short the threads and ruin the silk. Instead, silkworm cocoons are boiled. The heat kills the silkworms and the water makes the cocoons easier to unravel. Often, the silkworm itself is eaten (see also below). The adult phase (the moth) cannot fly. The silkmoths have a wingspan of 3-5 cm (1.5 - 2 inches) and a white hairy body. Females have about twice to three times the bulk of males (for they are carrying many eggs), but are similarly colored. Adults in the Bombycidae have reduced mouth parts and do not feed.
Silkworms Life Cycle | Index
© Herp Center - Richard Brooks
© Herp Center - Richard Brooks