1101 



PRACTICE OV AGRICULTURE. 



Pakx III. 



CHAr. XI. 



Insects and Worms which are or may be sul^jected to Culture. 



7594. The silkworm and the honey-bee are the two most valuable insects in Europe. 

 The first, from its great importance, has recently engaged the attention of the legislature, 

 no less than of private individuals, who have embarked large sums in the attempts now 

 making to introduce its culture in this country on a large scale. 



7595. The silkworm is the larva or caterpillar of a moth (^ombyx mori F.,Jig. 959.) : 



95c 



it is a native of China, and was introduced into Europe A.D. 160. When full grown 

 the worm is nearly three inches long, of a yellowish grey colour, with a horn-like pro- 

 cess on the last joint of the body. 



7596. In Italy and other silk countries the eggs are carefully preserved in some place of cool and even 

 temperature, where they remain until the new leaves of the white mulberry, which is its natural food, 

 are produced. The object is to hatch the eggs precisely at this time, that the new-born worm may be fed 

 on food suitable to its infant state. A grower of silk never hatches his whole stock of eggs at once, as a 

 night's frost will frequently destroy the leaves. Lettuce answers well in this stage of the worm's exist- 

 ence; but if it is fed entirely upon this plant the silk is of a very inferior descriiition, and is, indeed, 

 perfectly useless. The pabulum of the white mulberry, in fact, is superior in nutritious matter to that of 

 all others. The leaves in the autumn succeeding to those stripped in the spring, are commonly given to 

 cattle and pigs, who fatten upon them exceedingly. There is an unfounded prejudice in many silk 

 countries that the silk produced from the second leaf is inferior to the spring crop, and in France and Italy 

 the vernal leaf only is used. In India the mulberry tree is grown in moist places, like the osier in England, 

 and produces from three to six crops annually : the prejudice therefore of the Italian and French growers 

 against the second crop is unfounded. The real fact seems to be, that the worms are more difficult to 

 breed in autumn than in spring, from the great change of temperature, against which the growers in 

 general make no artificial provision. Another reason may probably be, that the silk is reeled with greater 

 economy and advantage in the height of summer, when the length of the days, and the heat of the we;ither, 

 is then sufficient to dry the thead in this operation. The native reelers of these countries are entirely un. 

 accustomed to use artificial methods for creating a regulated temperature in houses or manufactories. 



7597. The ventilation and cleaulincss of the nursery or fcedin^f apartments, and the preservation of a 

 regular heat within them, are highly important to the health of the worm. These points are much neglected 

 on the Continent, where the nurseries are usually situated in the midst of the mulberry plantations, ex- 

 posed to the external air, and seldom cleaned. It was satisfactorily ascertained by M. Guyton de Morveau 

 a few years ago, that a ruinous and unexpected mortality, which then raged among the worms, arose 

 chiefly from want of ventilation and cleanliness. It has likewise been proved, by experiments lately made 

 on a sufficiently large scale in Devonshire, that less mortality prevails among the worms in England than 

 either in France or Italy. 



7598. In about six iveeks the worm reaches its full size, previously casting its skin four" times, and ab- 

 staining from food for some time before each change ; at these periods the worms are very sickly, and a 

 creat mortality generally takes place. When full grown and about to spin, they exhibit symptoms of rest- 

 lessness and uneasiness; small twigs of birch, or of other slender trees, are set up in the boxes or shelves; 

 upon these the worms climb, each fixing upon its own berth. As it sometimes happens that two worms 

 spin together, forming what is called a double cocoon, this must be carefully prevented by separating them; 

 such a cocoon not only being difficult to run off when reeled, but two fibres are produced injurious to the 

 size of the thread : the double cocoons are therefore always wound off by themselves. In preparing its 

 case or cocoon, the worm first forms a loose envelopement of silken fibres, and then proceeds to enwrap 

 itself in a ball or case of an oval form, and finally changes into the pupa or chrysalis ; and after being thus 

 enclosed for about fifteen days, becomes a moth. This, however, is always prevented when the animal is 

 not kept for breeding, otherwise the hole formed by the moth in effecting its escape would destroy the 

 continuity of the silk, and prevent its reeling. The chrysalides are killed by two processes, by baking in 

 an oven, or by letting steam into a tiglit chest enclosing the cocoons. The latter method is preferable, as 

 the heat can be better regulated. 



7599. The cocoon, after the chrysalis is killed, is either reeled off at once, or sold to others who make 

 this a distinct trade. The silk, as formed by the animal, is so very fine, that if each cocoon was reeled 

 separately it would be totally unfit for use ; the ends of four are therefore joined and reeled together out 

 of warm water, which softening their natural gum, makes them stick together so as to form one strong 

 smooth thread. When the filament of any single cocoon breaks, or is exhausted, its place is suppHed by 

 a new one, so that the united thread may be wound to any length ; the single filaments of the newly added 

 cocoons are simply joined by being laid on the thread, to which they adhere by their gum. The old appa. 

 ratus for reeling merely consists of a large metal basin of water, under which is a fire to keep it hot, and a 

 reel of a poor and even rude construction : some important improvements, however, have been recently 

 made in this machine. In reeling it is desirable that a round thread of equal thickness and smoothness 

 should be produced, having the filaments of which it is composed as equal and as firmly united as possible. 

 When the skein is quite dry, it is taken off the reel, and a tie is made with refuse silk at its two ends ; it 

 is then doubled into a hank, and is ready for sale. In this state it arrives in England, and is called raw 



