Columbia Encyclopedia World Factbook Columbia Gazetteer American Heritage Coll. Many varieties of silk-spinning worms and insects are known, but the silkworm of commerce is the larva of the Bombyx mori, or mulberry silkworm, and other closely related moths. Wild silk is the product of the tussah worm of India and China, which feeds on oaks. It is now semicultivated, as groves of dwarf trees are provided for its feeding. It spins a coarser, flatter, yellower filament than the Bombyx mori, and the color does not boil out with the gum.
Tussah silk is a rough, durable, washable fabric known as shantung or pongee.
In silk manufacture, the first operation is reeling. The cocoons, having been sorted for color and texture, are steamed or placed in warm water to soften the natural gum. This is called raw silk. Formerly a hand process, this work is now done in Europe and in some parts of the Orient in factories on simple machines called filatures. The next step, called throwing, is preparing the raw silk for the loom by twisting and doubling it to the required strength and thickness.