The silkworm, scientifically known as Bombyx mori, is an insect primarily recognized for its ability to produce silk. This domesticated species undergoes a complete transformation. This process of metamorphosis is central to understanding the silkworm’s life and its contribution to silk production.
The Silkworm Life Cycle
The life cycle of the silkworm typically spans six to eight weeks, progressing through four main stages: egg, larva, pupa, and adult moth. The cycle begins when a female moth lays tiny, pinhead-sized eggs, usually between 300 to 500 at a time. These eggs remain dormant until warmer conditions stimulate hatching, which can take 7 to 14 days, depending on temperature.
Upon hatching, larvae, commonly known as silkworms or caterpillars, emerge. These newly emerged larvae are small, about 2-3 mm long, and initially appear dark or hairy. The larval stage is characterized by voracious feeding, primarily on mulberry leaves, and lasts approximately 20-28 days. During this period, the silkworm grows significantly, increasing its weight by thousands of times, and undergoes four molts, shedding its skin. After the fourth molt, the larva enters its fifth and final instar, preparing for the next stage.
The Cocoon’s Role in Metamorphosis
Once the silkworm larva reaches its full size, it ceases feeding and begins to spin a protective silk cocoon around itself. This process typically takes about 48 to 72 hours. The cocoon serves as the crucial chamber where the larva transforms into a pupa.
The silk used to construct the cocoon is a continuous filament produced from modified salivary glands, consisting primarily of two proteins: fibroin, which forms the core of the silk thread, and sericin, a gummy substance that binds the fibroin filaments together. Within this cocoon, larval organs dissolve, and adult organs begin to form during the pupal stage. The pupa, initially soft and white, gradually hardens and darkens, developing inside the cocoon for typically 10-14 days.
The Adult Moth: Final Transformation
The final stage of the silkworm’s life cycle is the emergence of the adult moth. The adult Bombyx mori moth is characterized by a thick, fuzzy, creamy-white body and a wingspan of about 40-50 mm. Unlike many other moths, the domesticated silkworm moth has underdeveloped mouthparts and does not feed during its brief adult life, which typically lasts only two to three days.
The adult moth is also unable to fly, a result of thousands of years of domestication and selective breeding, as its body is too heavy for its small wings. The primary purpose of the adult moth is reproduction; females lay eggs to begin the life cycle anew before they die. This transformation from a leaf-eating larva to a non-feeding, flightless moth highlights the changes that occur within the silkworm’s short lifespan.