The industry in which farmers raise silkworms (larvae of silkworm-moth) to make cocoons is called “sericultural industry.” Related to this industry, there are also ”silkworm egg producers” who supply silkworm eggs, called Sanshu(Seeds of Silkworms), to silk-raising farmers and “mulberry plant suppliers” who supply young mulberry plants to create mulberry fields.
During the Meiji Period, farmers were able to raise silkworms only once a year in spring under natural conditions, but now they can raise them six times or more a year; in spring, summer, early fall, and late fall (end of fall, early winter).
Life cycle and morphology of silkworms
Silkworms are holometabolous insects which have four growth stages during their lifetime; egg, larva, pupa, and adult. A larva hatched from egg undergoes four moulting cycles in about 25 days and transforms into a Jukusan or a mature larva. It makes a cocoon by emitting filament for 2 to 3 days and transforms into a pupa in another 2 to 3 days, and then emerges as a moth in about 10 days.
- Egg laying of silkworm moths
A silkworm moth lays about 500 silkworm eggs.
- Gisan , Kego (Newly hatched larvae)
Newly hatched larvae, which have not eaten any food yet, are called Gisan(ant worms) or Kego (hairy worms) because they look like ants from their black body hair.
- Larva (5th instar)
The body weight of the 5th-instar larva after has undergone four moults increases by about 10,000 times compared with a newly hatched larvae.
- Eiken (Cocooning)
Silkworm’s spinning to make cocoons is called”cocooning.” They continue to emit a cocoon filament about 1,300－1,500 m long for 2 to 3 days. The thickness of a cocoon filament they emit is about one fourth of a human hair.
The weight of a cocoon of a silkworm which is raised in present-day is about 2.0 g.