SILK 



453 



States of America and the British colonies are 

 making eflorts to introduce the cultivation of the 

 B. mart; the only hindrance being in the high 

 price of labour for cocoon reeling. The B. mori is 

 univoltine or annual ; but the B. fortunntus and B. 

 crassi, which are confined to Bengal, are multivoltine 

 i-e. they produce several broods annually. For 

 wild silks not from mulberry feeders, see page 456. 



Classification. The silk- producing Lepioopterous 

 insects are of many species, possessing very marked 

 structural differences, whilst the variety and quiet 

 beauty of their colours, and in many species their 

 jarge size, contribute greatly to the charm of study- 

 ing this branch of natural history. They belong 

 to the order Lepidoptera, sub-order Heterocera or 

 Moths, group Bombycina, and to several of the 

 twenty-seven or more families which compose this 

 group, the most important being the Bombycidse 

 and tin; Saturnidse. All the Saturnidse are silk- 

 producers, but not all the Bombycidte. Recent 

 researches have resulted in adding many new or 

 previously unknown species to the list of silk- 

 producers, and the known number is now upwards 

 of 400, and the list is by no means complete. 



The Bombycidie have a very short and rudi- 

 mentary proboscis, live for a very brief time in 

 their perfect state, and take little or no food ; 

 the body is thick and hairy ; the antennae are 

 pectinated. The caterpillars feed on the leaves 

 and other tender parte of trees or other plants; the 

 chrysalises are enclosed in a cocoon of silk, which 

 gives to some of the species a great economical 

 importance. The most important is the Common 

 .Silkworm (Bombyx mori), cultivated chiefly in 

 China, Japan, Italy, and France. The perfect 



Fig. 1. Common Silkworm (Bnrobyx mori): 



a, larva, full grown ; ft, larva, seriposlting ; c, cocoon ; 



d, chrysalis ; e, female moth ; /, male moth. 



moth is about an inch in length, the female rather 

 larger than the male ; the (rings meeting like the 

 aides of a roof ; the colour pale buft' with a broad 

 pale brown bar across cne upper wings. The 

 females generally die very soon after they have 

 laiil their eggs, and the males do not survive much 

 longer. The eggs are numerous, about the size of 

 a pin's hfiul, not attached together, but fastened 

 to the surface on which they are laid by a gummy 



substance, which, when dry, becomes silky. In 

 Europe they are laid in spring, and are hatched in 

 summer. The caterpillar is at first very small, not 

 more than a quarter of an inch in length, but 

 rapidly increases in size, till, when full grown, it is 

 nearly 3 inches long. It is of a yellowish-gray 

 colour. The head is large. On the upper part of 

 the last joint of the body is a horn-like process. 

 The skin is changed four times during the growth 

 of the caterpillar. Before each change of the skin 

 it becomes lethargic and ceases to eat, whereas at 

 other times it is very voracious. When the skin is 

 ready to be cast off it bursts at the forepart, and 

 the caterpillar then, by continually writhing its 

 body, without moving from the spot, thrusts it 

 backwards ; but silkworms frequently die during 

 the change of skin. A very rapid increase of size 

 takes place whilst the new skin is still soft. The 

 natural food of the silkworm is the leaves of the 

 white mulberry, but it will also feed on the leaves 

 of some other plants, as the black mulberry 

 and the lettuce. When so fed, however, it pro- 

 duces silk of inferior quality. The silk-producing 

 organs are two large glands (sericteria) containing 

 a viscid substance ; they extend along great part 

 of the body, and terminate in two seripositors in 

 the mouth. These glands become very large when 

 the change to the chrysalis or pupa state is about 

 to take place. When about to spin its cocoon the 

 silkworm ceases to eat, and first produces the loose 

 rough fibre which forms the outer part of the 

 cocoon, and then the more closely disposed and 

 valuable fibre of its interior. In this process the 

 position of the hinder part of the body is little 

 changed, but the head is moved from one point to 

 another ; and the cocoon when finished is much 

 shorter than the body, which, however, being bent, 

 is completely enclosed in it. The cocoon is about 

 the size of a pigeon's egg. Each fibre of silk or 

 bare, when examined by a microscope, is seen to 

 be double or of two brins, being equally derived 

 from the two silk-producing organs of the cater- 

 pillar. The have or double thread often exceeds 

 1100 feet in length. The time of the silkworm's 

 life in the caterpillar state is generally about eight 

 weeks. About five days are occupied in the spin- 

 ning of the cocoon, after which about two or three 

 weeks elapse before the cocoon bursts and the per- 

 fect insect comes forth. The opening of the end of 

 the cocoon by the moth for its escape is, however, 

 injurious to the free and perfect reeling of the silk 

 from the cocoon, and the silkworm rearer prevents 

 this by throwing all the cocoons into hot water or 

 more usually into an oven, called in France 

 (touffoir, stchoir, heated by hot air or by steam, 

 except those which he intends to keep for breeding. 

 These he selects with care, so that he may have 

 about an equal number of male and female insects, 

 the females being known even in the chrysalis 

 state by their larger size. The cocoons intended 

 for the production of moths are placed on a cloth 

 in a somewhat darkened room, of which the tem- 

 perature is near, but does not exceed, 72 F. ; and 

 the moths, when produced, show no inclination to 

 fly away, but remain on the cloth, lay their eggs, 

 and die there. It is an interesting peculiarity of 

 this valuable species of moth that neither in the 

 caterpillar nor in the winged state does it show 

 that restless disposition which belongs to many 

 others, the caterpillars remaining contentedly in 

 the trays or boxes in which they are placed, feeding 

 on the leaves with which they are there supplied^ 

 and at last only seeking a proper place for making 

 their cocoons for their covering and protection. 

 Whilst assuming the chrysalis state small bundles 

 of twigs are placed above the feeding-trays for the 

 worms at their last caterpillar stage to resort to 

 for cocoon building. Owing to this peculiarity or 



