Wild silkworms, native to Japan, are large in size and belong to Bombycidae, Lepidoptera. They hatch once a year and the larvae completely metamorphose in five years over four winters.
These silkworms, also called “Yamako,” “Yama-mayu” and “Yama-mai,” live on the leaves of Japanese chestnut oaks and other wild forest trees.
A silk moth egg, 2.8 mm long, 2.6 mm wide, 1.9 mm thick, is shaped like a flat ball. Wintered eggs hatch from early to mid May.
Hatched larvae instinctively move toward sprouting oak trees.
Hatched larvae (first-instar larvae) thrive on Japanese chestnut oaks and molt four times. Every time they molt, their name changes from second- through fifth-stage larvae.
Cocooning begins within two months after hatching
“Cocooning” is a process to spin a cocoon.
Fifth-stage larvae move around to find a place for cocooning. Upon finding the right place, they pull in several leaves and spin to secure a footing.
While spinning and skillfully swinging their bodies, they produce oval cocoons. Cocooning takes whole three nights and days to complete.
The adult moth creeps out by dissolving the cocoon tip with saliva. It takes half an hour to stretch out wings. A moth has a wingspan of 18 cm, and the wing has ocelli.
Adult moths, emerging from a cocoon, mate and lay eggs one or several days after mating.
An adult moth dies in one week or so after emerging, as its mouth has degraded and takes in no feed.