Varieties of Silk Moths

There are between three and four hundred varieties of moths that produce silk cocoons, many of these varieties being found in America. Only a few produce cocoons of the kind and quantity that make it profitable to collect them. Most silk comes from a single variety known to science as the Bombyx mori. This silk moth, or silkworm as we shall call it, has been raised for hundreds and even thousands of years. It is correctly called the domesticated silkworm. From just what wild variety it originally came is not known. It has probably changed greatly during its age-long process of culture. By the selection of only the larger ones for breeding purposes, this variety has been increased in size, with consequent enlargement of the cocoon. It has lost its power of flight.The wings of the full-grown moth are practically useless. At the caterpillar stage it has lost its sight. The constant care that man has given to thousands of generations of worms has made it unnecessary for them to see or fly; these functions therefore have been lost. All necessary movements are provided for by human attendants, who carry the worms to the feeding places and supply them with food. The Bombyx mori, the domestic silkworm, is white or cream-colored, whereas the wild varieties vary widely in color. Brown is very common.Stages in. the life of a silkworm.-The silkworms of all varieties pass through four marked stages: first we find them as eggs; second, as caterpillars or worms; third, as chrysalides, inside of the cocoons; and fourth, as full-grown moths. It takes from twenty to thirty days for the eggs to hatch. The caterpillar stage lasts about 3o days. The chrysalis stage lasts but a few days, and the moths die as soon as they have mated and laid the new generation of eggs.The Bombyx mori produces but one new generation each year. For this reason it is called univoltine. Some of the wild species of silkworms, however, annually produce two, three, and even more generations. The common Chinese wild silkworms produce as many as seven crops each year in the Hong Kong district, while a variety in Bengal, India, produces eight generations. These varieties are called multivoltine. The univoltine is preferred for cultivation to the many multivoltine species because it produces the finest and strongest silk. In the attempt to use the cocoons from the multivoltine species there is a great deal of waste; it is utterly impossible to reel the cocoons of some varieties.