Lifecycle: The silk moth has been domesticated for 5,000 years and is no longer found in the wild. Selective breeding has made it too large to fly, but it does not have to crawl far to find a mate. The female lays her eggs soon after mating. The tiny caterpillar, or larva, is fully grown at about six weeks. It then attaches itself to a stalk and spins a large silk cocoon. The silk is produced by the caterpillar’s salivary glands and comes out through an organ called a spinneret that is near the mouthparts. 

It takes a caterpillar over two days to spin its cocoon. Within this protective casing, it pupates, transforming itself into a winged moth. The adult moth emerges after two to three weeks. But the moth damages the silk as it hatches, so most cocoons are collected earlier and the pupae inside are killed. The largest and finest cocoons are left to produce adults for breeding.

Silkworm and Man: Several insects and spiders produce silk, but only the silk moth produces it in large enough quantities for commercial use. The Chinese are credited with discovering how to unwind this fiber from cocoons and turn it into a luxurious, strong fabric. The first silk came from wild moths, but soon the Chinese began breeding them. By selecting only large moths and those that made the finest silk, they developed the huge flightless insects of today. Before the silk can be unwound, the cocoon must be soaked in very hot water to dissolve the sericin, a “glue” that makes the silk stick to itself. As the ends of the silk float free, they can be wound onto a reel. Because silk is so fine, several strands can be wound together. The remaining sericin helps to stick the fibers together.

Food and Feeding: The caterpillar must eat nearly all the time. When it is fed only mulberry leaves, it eats continuously and grows quickly. It will consume other leafy plants but tests have shown that caterpillars given a mixed diet do not grow as rapidly or produce silk as fine as those fed only mulberry leaves. When fully grown at about six weeks, the caterpillar stops eating and spins the cocoon in which it will change into an adult. The main function of the adult moth is to breed. Unlike the caterpillar, the adult moth does not need to feed and thus does not possess true mouthparts.

Key Facts:
Sizes:
Wings: 2 pairs
Wingspan: 4 in.
Length: Caterpillar, over 3 in.
Mouthparts: Caterpillar, 1 pair for chewing. Adult moth has only remnants of the caterpillar’s mouthparts

Breeding:
Eggs: 300-500
Egg to pupa: Varies with temperature
Pupa to hatching: 2-3 weeks

Lifestyle:
Habit: Nonflying, domesticated species
Diet: Mulberry leaves
Lifespan: Adult, 3-5 days. Caterpillar, 4-6 weeks

Related Species: Related wild species include the Indian tussah silk moth, Antheraea paphia, and the atlas moth, Attacus atlas.
Distribution: Once native to Asia, the silk moth is now bred mainly in Japan and China. It is also farmed in the Soviet Union, India, Pakistan, Turkey, France, and Italy.
Conservation: The silk moth has been extinct in the wild for centuries. It now lives in large domesticated groups that are bred for size and silk quality. It is carefully protected from disease.

Lifecycle of the Silk Moth:
1. Eggs: Female lays up to 500 eggs on a leaf. Adults die soon afterward.
2. Larva: Born black and hairy. Hatching time depends on the temperature during incubation.
3. Caterpillar: As it grows, the larva sheds several layers of skin and becomes white and smooth.
4. Cocoon: After 6 weeks of feeding, the caterpillar finds a stalk and spins a silk cocoon, where it pupates.
5. Adult Moth: The adults must mate soon after emerging from the cocoon. The female secretes a strong smelling substance that the male detects with special hairs on his enlarged antennae.

Did You Know: 
Legend has it that China lost its monopoly on silk in the fourth century when moth eggs were smuggled out in the headdress of a Chinese princess who married an Indian prince.
The weeding dress of Queen Elizabeth II was made of silk produced by moths in Britain.
Silk is graded according to its fineness, or denier. Denier is the weight of a 1475 foot length of silk.
“Wild silk” is produced by relatives of the silk moth in cocoons found in the wild.

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