2. The Silk Worm
Names and Types of Silk Worms
The textile fibre known as silk is a filament secreted by one of two general types of moth larvæ—the cultivated and the wild. The largest proportion is, of course, made up of the former, produced by the worm known as the Bombyx mori, while the most common type of wild silk worm is called the Tussah. The name Bombyx mori comes from the name of the family to which the silk worm belongs: the Bombycidoe (spinners), and mori, from the morus multicaulis or mulberry tree, on the leaves of which it feeds. The species Sericaria mori, or silk worm of the mulberry, belongs to the generic class of Lepidoptera or scaly-winged insects.
Bombyx Mori
The Bombyx mori, with which we are chiefly concerned, is divided into other groups according to the cycle of reproduction. The annuals reproduce once a year, and sixty per cent of the silk worms belong to this class. The bivoltines reproduce twice a year, and the polyvoltines, several times during the year, the first crop being the best.
Full Grown Worms
The study and development of the various phases through which the silk worm passes, leading up to its production of the actual filament, have been a subject of intense research in many parts of the world for a great number of centuries. The present silk worm is nothing more than a highly specialized product of a long train of artificial cultivation.
Stages of Growth
The cultivated silk worm passes through four changes in its life of two months, i.e., egg, larva, chrysalis (or pupa), and adult—a cream-white moth which is about one inch in length. The moths live only a few days, during which mating takes place, and the female lays several hundred eggs; after about six months these eggs hatch into worms. The latter pass through what are known as four “molts,” or shedding of the skin, before the worm matures, spins its cocoon, becomes a chrysalis, and finally emerges as a moth. This, very briefly, is the life history of the silk worm.