SILKWORMS, entomologically, any cater pillar which spins a cocoon of silky fibre; pop ularly, the various species which yield a fibre used commercially. All are caterpillars of moths and feed upon foliage of various trees and shrubs. Among the less important species the following are probably best known: The Japanese oak-feeding silk-moth (Bombvx yama mai) is noted for its green-tinted silk, which is used in Japan and Ghina for embroidery; a close relative (B. peryni), also an oak-feeding insect, is a native of northern China, where its large grayish-brown Cocoons are used to a considerable extent for threads and various fabrics. The Chinese also use for the manu facture of a soft fabric the gray silk of an allied species (B. Cynthia), which feeds on the tree of heaven (Ailanthus glandulosa). Since the thread cannot be reeled the silk is obtained by carding methods. So far as known these species have not been extensively employed commercially except in the Orient, though they have been used tentatively in France and other silk-manufacturing countries. The tussur or tusseh moth (Antheraa paphia) spins a hard grayish-white cocoon from which the natives of India, where the species is indigenous, manu facture tussur silk. The Bengalese use the pure white silk of the boro poloo (Bombyx textor) and the yellow silk of the dasee-worm (B. fortunatus) for making a silk cloth which rarely reaches the world's markets because of its in ferior quality. Several North and South Amer ican species yield silk which has not become commercially important. The native silkworms of the United States. Mexico and Central Amer ica have never been properly commercially ex ploited or cultivated; but several varieties possess qualities which would seem to promise success to him who would raise them scien tifically. They are hardy and spin large quanti ties of excellent, strong silk. They feed upon a much larger variety of food than do the silk worms commercially known to the Old World. This comprises the leaves of the oak, apple, maple, hickory, willow, sycamore and many other trees. One of the most promising of these American silkworms (Telea polyphemus) is a large buff-colored moth. The cocoon threads are bound together with a hard gluey matter which has to be softened before un winding can be done. The Tropwluna, the larva of which feeds on the leaves of several forest trees, is somewhat similar to the fore going and both resemble the Yamanai. Culti vation and proper selection would undoubtedly improve them commercially. The amount of silk they produce is far greater and stronger than is produced by the Chinese silkworm, but the thread cannot be so easily reeled.
The most important and most widely dis seminated species of silkworm is Bombyx mori, which belongs to the family Bombycidw, a native either of northern China or of Bengal. It seems to have been domesticated at a very early date, which is placed by Chinese authori ties at 2600 B.c., when the wife of Emperor Hoang-ti began feeding the caterpillars In 552 two monks brought eggs to Constantinople, superintended experiments in cultivating the worms and turned the industry over to the Emperor Justinian, by whom it was monopo lized. Neighboring peoples soon took it up,
however; and now many countries, especially those of the Mediterranean region, Persia, India and Arabia, raise silk in commercial quantities.
The commercial silkworm is the larva of a large moth with a short thick body, stout legs and broad white wings crossed by several black lines or by a pale bar upon the anterior pair. In early summer the females lay from 200 to 500 bluish eggs, about as large as a pin's head, singly upon any convenient surface, gluing them there by a mucilaginous secretion, silky when dry. These do not hatch until the following spring. Then the larva, about one-quarter of an inch long and yellowish-gray or brownish, begin to feed, and soon consume about their own weight of foliage daily and increase rapidly in size. When about 10 days old they become lethargic and stop eating until after they have cast their skins. In this operation the old skin bursts near the front and the cater pillar squirms itself out, leaving the old skin attached to the branch or leaf upon which it was stationed. The worms rapidly increase in size immediately after the molt, then steadily diminish as the time for the next molt .ap proaches. The process is performed four times before the caterpillar spins its cocoon, which it does when about six weeks old. At this time it is about three inches long and half an inch in diameter, has 12 visible body segments,-three pairs of true legs and five pairs of pro-legs. It now ceases to feed, empties its alimentary tract, and seems to shrink in size. The spinning then begins by the insect making first an outer network known as the "floss," and then wind ing the silk in a continuous thread around its body which continues to decrease in size. The completed cocoon is considerably shorter than the caterpillar itself, being only about one and one-half inches long. The operation of spin: ning occupies about five days, during which time the insect usually produces from 2,000 to 3,000 feet of silk, which, when microscopically ex amined, is seen to consist of two blended strands. These are produced by special glands (sericteria) which extend nearly the whole length of the body and terminate in apertures (spinnerets) situated in the mouth. In from 15 to 20 days after the chrysalis has been formed the adult insect emerges, lays its eggs and dies. It has been estimated that there are about 20, 000 to 40,000 eggs, popularly known as °seed° in an ounce. About one ounce of eggs will yield 100 pounds of cocoons or nine pounds of raw silk. From 15 to 20 pounds of good mul berry leaves should yield one pound of cocoons; and a well-grown mulberry tree should yield about 100 pounds of leaves. The amount of space allowed for the caterpillars produced from an ounce of eggs varies from one square yard, immediately after hatching, to about 64 square yards when spinning time arrives —each change being double the previous space: 2, 4, 8, 16 and 32.