Silk-worm  (Bombyx mori ) lives on the Mulberry, and is bred for the fibers of the cocoon. It originally came from southern Asia, but is now extensively cultivated in China, Japan and southern Europe for the purpose of obtaining its silk. The cultivation of the silkworm is dependent almost entirely on the supply of these leaves.


On the low, moist, alluvial soils of the East, slips of this tree are planted in close and continuous lines, and six to eight weeks afterwards they are six feet high, and the leaf-crop allows of six to ten broods being produced in the course of six months. In Europe it is not unusual for more than one brood to be produced, and the female lays her eggs towards the end of the summer; but they do not hatch until the following spring, when the leaves appear. In Asia, during the season, the eggs hatch eight to ten days after laying. The caterpillar feeds persistently, and rapidly grows; at the end of a month it moults, and this happens four times in all before it starts to make its cocoon.


The female moth deposits in July three to five hundred eggs, from which the white caterpillars (a) emerge in the following spring, at the period when the white mulberry tree blooms, upon the leaves of which they feed. The caterpillars change their skins four times and are full grown in about a month. They now spin a cocoon (c), which is generally completed in three and a half days, and five days later they change into pupæ (b). The pupal stage lasts from fourteen to nineteen days. The cocoons furnish the silk, and the pupæ are generally killed on the tenth day by heat.


The silk is produced from spinnerets, two apertures in the head, the two filaments joining as they appear to form a very strong thread from five hundred to one thousand yards long. This the caterpillar wraps round its body until it is completely covered, and then it passes into the chrysalis state. Unless the grey moth is wanted for egg-laying, the chrysalis is killed by putting the cocoon in a hot oven, for if allowed to appear it cuts through some of the more valuable parts of the silk.


The next process is to wind as much as possible off the cocoons into hanks. In Europe and in some Oriental towns this is done with improved machinery in factories called filatures. It is usually begun when the cocoons are fresh. Each operator has before her a basin of hot water, the temperature of which is regulated by a steam-pipe or a fire, and overhead is a reel turning slowly. After removing the outside flossy covering, the operator places the cocoons in the basin, with the result that the hot water softens the natural gum that is in the silk, and allows it to be wound off. The filaments are passed through several glass eyes, and crossed, and thus become glued together into a thread which is called “singles,” and when further prepared is known as “thrown silk.” The singles are reeled into large hanks being called a “moss,” and each bundle a “book.”

In this form, Asiatic silk is imported into Europe and the United States. The quantity of such silk obtained from one cocoon is very small—seldom up to a thousand yards, generally not more than five hundred yards. The remainder of the cocoon is either too flossy or too entangled to be wound. This waste portion forms the material from which spun silk is prepared. Five to six hundred cocoons weigh two pounds, and twenty pounds of cocoons yield two pounds of spun silk. The eggs of the silkworm were first brought to Europe by two Christian monks in 555 A. D., who took them in hollow sticks to Constantinople, whence the cultivation of the silkworm rapidly spread to other parts.