The silkworm is not a worm, but the larval stage of a small, domesticated moth, Bombyx mori. This creature is prized globally for its unique ability to produce silk, a textile fiber known for its strength and luster. Originating in ancient China over 5,000 years ago, the production of silk has shaped centuries of trade and culture. Today, its existence is entirely dependent on human care, making it one of the most thoroughly domesticated insects on the planet.
Biological Identity and Life Cycle Stages
The silkworm is classified as Bombyx mori, a species within the family Bombycidae, which belongs to the order Lepidoptera (moths and butterflies). Its life cycle involves a complete metamorphosis, progressing through four distinct stages: egg, larva, pupa, and adult moth.
The female moth lays hundreds of tiny eggs, which are incubated to hatch into the larval stage, the silkworm. This larva is a voracious eater, growing rapidly over about four weeks as it progresses through five growth phases, known as instars. The silkworm molts, or sheds its skin, four times during this process as its body size increases.
Once the larva is fully mature, it stops feeding and begins to spin the silk cocoon, a protective casing around itself. Inside this cocoon, the larva transforms into the pupa, an immobile stage where the insect reorganizes its body for adulthood. After a few weeks, the pupa metamorphoses into the final stage, the adult moth, which lives only a short time to reproduce.
The Specialized Practice of Sericulture
Sericulture is the practice of rearing silkworms to harvest the raw silk they produce. The process begins with the incubation of eggs and the controlled feeding of the newly hatched larvae, which require enormous quantities of fresh mulberry leaves. As the silkworms mature, their silk glands (modified salivary glands) become engorged with fibroin, a liquid protein.
To create its cocoon, the silkworm secretes liquid fibroin and a gummy protein called sericin through the spinneret, a single exit tube on its head. The larva moves its head in a figure-eight pattern, layering the continuous filament around itself. This filament hardens immediately upon contact with the air, resulting in a single strand measuring between 600 and 900 meters long.
The timing of the harvest is important for the quality of the silk fiber. Cocoons must be collected and processed before the moth inside can complete its development and emerge. If the moth breaks through, it secretes an enzyme that dissolves the silk, cutting the long, continuous strand into short, unusable pieces. To prevent this, the cocoons are subjected to heat (often steam or boiling water), which kills the pupa and simultaneously softens the sericin gum.
The softened cocoons are then ready for reeling, where workers locate the outer end of the filament and unwind it onto a reel. This process combines threads from several cocoons to create a single, usable strand of raw silk. The sericin remains on the fiber in this raw state, giving it a rougher texture. To produce finished silk, this gum must be stripped away through degumming, revealing the smooth, lustrous fibroin fiber underneath.
The Uniqueness of the Domesticated Silkworm
The silkworm, Bombyx mori, is a product of thousands of years of selective breeding. Unlike its wild ancestor, the Chinese wild silkmoth (Bombyx mandarina), the domesticated species is entirely dependent on human intervention for its survival. Over time, physical traits necessary for life in the wild have been lost.
The adult silk moth is unable to fly due to its heavy body and small wings. Furthermore, the moth has lost its functional mouthparts and does not feed at all during its short adult life. The larvae have also lost their natural camouflage, having a pale, leucistic appearance, and cannot survive without human assistance in feeding and protection from predators.
Its diet is also highly specialized, consisting almost exclusively of white mulberry leaves, though a few other plants can be substituted. This complete inability to survive outside of a controlled environment underscores how profoundly selective breeding has altered the species to maximize silk production. The domesticated silkworm exists today solely as a biological machine for creating the world’s most luxurious natural fiber.