The eggs from which the silkworms are hatched are very fragile, and for this reason the butterflies are made to deposit them on pieces of bast paper about a foot long and eight inches wide. Each piece is covered with about 45,000 separate eggs, and from these the caterpillars creep out on the cardboard, or whatever fiber has been used to receive the eggs.
The Japanese silkworms differ in several respects from those of Europe, principally in being smaller. The grubs are one-fourth smaller, while of the cocoons a kilogram holds 850 of the white Japanese spinners, but only 500 of the Brianza breed of North Italy. White spinners (Japanese, Shiro-ko, white children) and green spinners (yellowish green in color and called by the Japanese Kin-ko, good children), are the favorite Japanese breeds.
Almost all species of silkworms are characterized during the caterpillar stage by four castings, a lazy life, and their diet of fresh mulberry leaves. Until the third casting they are fed on chopped leaves, four times a day. The room must be clean, dry, and free from draughts. Cleanliness is strictly essential in the room, the beds, the mulberry leaves, and the attendant. In Japan the work is done mostly by women.