Silkworm cocoon

“ As the silkworm spins its web by thus bending the fore part of the body back, and moves the hinder part of the body in such a way only as to enable it to reach the farther back with the fore part, it follows that it encloses itself in a cocoon much shorter than its own body, for soon after the beginning the whole is continued with the body in a bent position. ”

“ It is the most important of all insects to man, as from it alone all the silk of commerce is obtained. Its cocoon is of a beautiful yellow colour, varying in shade from orange to pale straw-colour; the silk of one cocoon weighs somewhere about three grains; it would therefore, at this calculation, take 1920 worms to spin one pound. The annual import of silk into this country alone is about 7,000,000 pounds, it must therefore take 13,440,000,000 Silkworms to supply us with silk yearly! The Silkworm feeds almost exclusively on the leaves of the mulberry. ”

“ We learn something of this Coan silkworm from Pliny, who tells us that it lived on the ash and oak and cypress tree; and from Clement of Alexandria and other of the Fathers we glean a little more—for instance, that the larva was covered with thick-set hairs, and that the cocoon was of a loose material something like a spider’s web. All this agrees in every particular with a certain large moth (Lasiocampa otus) , which spins a rough cocoon not unlike that of our Emperor moth, and lives in south-eastern Europe, feeding on the cypress and the oak. ”

“ The supply of waste silk is drawn from the following sources: (1) The silkworm, when commencing to spin, emits a dull, lustreless and uneven thread with which it suspends itself to the twigs and leaves of the tree upon which it has been feeding, or to the straws provided for it by attendants in the worm-rearing establishments: this first thread is unreelable, and, moreover, is often mixed with straw, leaves and twigs. (2) The outside layers of the true cocoon are too coarse and uneven for reeling ”

“ For this purpose it spins a winding-sheet of silk, or digs down into the ground and forms a case, or cocoon; or else it hangs itself by the tail, and becomes [Pg 388] strangely transformed into what we call a 'chrysalis.' From the cocoon, or chrysalis, as the case may be, the butterfly or moth sooner or later makes its appearance.
Fig. 1.—Dragon-fly moulting.
To give an idea of the great increase of growth in insects, let us take the case of the silkworm. At the time of hatching, the little worm weighs about the one-hundredth part of a grain; when fully grown, it weighs ninety-five grains. ”

“ Then there is what is known as "boiled waste," i.e., the inner layer or two of silk in a cocoon which cannot easily be reeled. The chrysalis and the skin of the silkworm are picked out and themselves form a by-product as manure; while the "boiled waste" is washed, baled, and exported for use in the manufacture of "noil" yarn as distinct from cotton yarn. Again, amongst the cocoons there sometimes occur what are known as "doubles," formed when two silkworms enclose themselves in one cocoon. ”

“ The silkworm butterfly is not pretty. It is whitish, tun-bellied, heavy. It does not fly like the others from flower to flower, for it takes no nourishment. As soon as it is out of the cocoon, it sets to work laying eggs; then it dies. Silkworm eggs are commonly called seed, a very good term, for the egg is the seed of the animal as the seed is the egg of the plant. Egg and seed correspond. They do not stifle all the cocoons in the vapor to wind them afterwards; they keep out a certain number so as to obtain butterflies and consequently eggs or seeds. ”

“ This larva feeds on the leaves of the mulberry tree, and when first produced is extremely small, and entirely black. In a few days it appears in a new habit, which is white, tinged with the colour of its food; and before it goes into its chrysalis state it changes its skin several times. When full grown it spins its cone of silk, which is its cocoon, in the same manner as other insects. The Moth possesses no beauty. The Silkworm is a native of China, whence the greater part of our silk is still imported ”

“ In this part of the work we notice the most perfect adaptation of the creature to the needs of man. While the silk threads from the cocoons of other species which might prove of value cannot be easily reeled off, those of the silkworm, when placed in hot water, readily separate, and can be gathered in a condition for spinning. Thus, while some success has been attained by carding the cocoons of other species, thereby making a fibre which has a certain utility, the silkworm alone yields material fitted for delicate fabrics. ”

“ If left to themselves, the silkworms when ready for spinning will spin the silk around their bodies until they are completely covered up, gradually forming a cocoon. In order to determine when they have finished spinning it was customary to take the cocoon and rattle it near the ear. ”

“ Proceeding onward, and protected from the fierce heat of the sun's rays by the pleasant shade of mountain pines, we were continually encountering horseloads of cocoons, the fruit of the industry of the Druse silk-rearer. The whole process, from hatching the silkworms' eggs till the moment that the worm becomes a cocoon, is one series of anxiety and labour to the peasant. The worms are so delicate that the smallest change of temperature exposes them to destruction, and the peasant can never confidently count upon reaping a harvest until the cocoon is fairly set. ”

“ Millions of cocoons of the Tusseh silkworm are annually collected in the jungle, and brought to the silk factories near Calcutta. In other parts the people gather and transplant them to the trees near their own dwellings, that they may watch over the safety of the caterpillars, which are very liable to be devoured by crows during the day time, and by bats at night.
The Arindy silkworm feeds only on the leaves of the Palmi Christi; it produces so delicate and flossy a silk that it cannot be wound from the cocoons ”

“ The rearing and management of silkworms is an innocent and agreeable pastime both to boys and girls, and it is very interesting in many points of view. One fact is, that while the caterpillars of all the other tribes of moths and butterflies, when they have arrived at a certain state of maturity, show a restless disposition, and wander about and hide themselves in a variety of places in order to spin their cocoons, the silkworm, on the contrary, is content to remain stationary in the open tray or box in which it may be placed. ”

“ Every day is to them a year, and has in a manner the four seasons; the morning is the spring, the middle of the day the summer, the evening the autumn, and the night the winter."
While it remains in the state of a caterpillar, the Silk-worm changes its coat four times, and previous to each moult refuses its food, and appears in a very sickly condition. As soon as its nest or cocoon is finished, and it has changed into the pupa-state, the cocoons are carefully removed from the place where the animal had formed them ”

“ When the moth is ready to leave its cell, it always softens the extremity of it by emitting a drop of fluid, and thus easily obtains for itself a passage. In the third volume of the Transactions of the Royal Asiatic Society (p. 543.) , Colonel Sykes gives the following account of the process by which the moth of the Kolisurra silk-worm liberates itself from confinement. “It discharges from its mouth a liquor, which dissolves or loosens that part of the cocoon adjoining to the cord which attaches it to the branch, causing a hole, and admitting of the passage of the moth. ”

“ They have to take good care of themselves while their wings are growing, for fear something will eat them up.
“In the silkworm, they wait till they have spun, and then they bake the cocoons to kill the animal inside, or else he would eat out. Then they unwind the silk. Each one lays about six or seven hundred eggs, so they can afford to kill a few.
“Some of the insects of this class are not so pleasant to have. The canker-worm belongs to it, and so does the moth that gets into houses and eats up woollen things. ”

“ On the other hand, those caterpillars known as 'silkworms' make a dense cocoon of pure silk, consisting of two layers, the outer of coarse and the inner of fine threads. Silken cocoons very similar in appearance are spun by the larvae of small Ichneumon-flies. Many pupae lie in a loose cocoon formed of a few interlacing threads, as for example the conspicuous black and yellow banded pupa of the Magpie-moth (Abraxas grossulariata) and the pupae of various leaf-beetles. Others again spin together the edges of leaves with connecting silken threads. ”

“ It is incomplete in the sense that the change is not of a very radical nature. But in the case of the silk worm moths, and moths and butterflies in general, the larva which hatches from the eggs has not even the most superficial resemblance to the adult insect, the fully-developed moth. This necessitates a complete change or metamorphosis in the form and structure of the insect before it can become mature. This great change is accomplished during the quiet pupal stage in the cocoon. ”

“ At the end of this time the silkworms change to a clear pink or flesh colour, and look semi-transparent; they refuse food, become restless, and prepare to spin their cocoon. Care should be taken to raise the walls of their tray or they will climb over and be lost. The cocoon nest should now be prepared by twisting the corners of a piece of writing-paper, and raising its edges into the form shown in the illustration. A number of these should be prepared and fixed to a piece of tape, with their pointed ends downwards ”

“ SILK-MOTHS.
These insects are in several respects interesting to us, more especially because they have varied largely at an early period of life, and the variations have been inherited at corresponding periods. As the value of the silk-moth depends entirely on the cocoon, every change in its structure and qualities has been carefully attended to, and races differing much in the cocoon, but hardly at all in the adult state, have been produced. With the races of most other domestic animals, the young resemble each other closely, whilst the adults differ much. ”

“ Inside the cocoon the worm remains, adequately protected from cold and damp, for nine months. It emerges as a winged moth, whose sole function in life apparently is to lay eggs to produce more silkworms.
Spinning such a cocoon with its three quite different layers requires extreme precision of movement. Nature has not allowed for any possible variations. ”

“ To fashion a sufficient shelter the larva supplements by its industry the small amount of silk at its disposal. With grains of sand artistically put together and connected by silky matter, it constructs a most solid cocoon—impenetrable to damp. ”

“ At this juncture a fluid is secreted from the mouth of the insect which so softens the silk as to make the escape of the moth a comparatively easy matter, while without this wise provision it might remain in its cell and exhaust itself in fruitless efforts to get out. Presently the fore legs appear, thrust out of the upper end of the cocoon, then the head crowned with its beautiful feather-like antennæ; and very soon a heavy looking object with a large plump body and soft clumsy little wings is drawn slowly out of the orifice, and stands before you in the free air. ”

“ When the right location is found it spins a very strong thread for the outside, fastening it securely to a small branch, and going back and forth with this strong silk until it assumes its proper shape and proportion. You will find it almost impossible to tear it open with your fingers, and only a sharp knife will enable you to see the contents. This strong outside is necessary for protection, as the woodpeckers are very fond of the larva and imago. After this strong outside is completed the silk is woven very loosely between it and the cocoon proper. ”

“ It is closely allied to the Cynthia or Ailanthus worm, with the same kind of silk and a similar cocoon, and feeds on the castor oil plant.
The diseases of silk worms naturally receive much attention. Like those afflicting mankind, they arise from bad air, resulting from too close confinement, bad food, and other adverse causes. The most fatal and wide-spread disease, and one which since 1854 has threatened the extermination of silk worms in Europe, is the pebrine. It is due to the presence of minute vegetable corpuscles, which attack both the worms and the eggs. ”

“ The [Pg 50] common silk-worm spins and suspends itself by its thread, long before it begins its cocoon. It appears probable, therefore, that there may have been wild varieties of this creature, or perhaps other species of the same genus, which in the earlier stages of their existence spun threads long enough for use. ”

“ In the occasional attempts which have been made to substitute spiders for silkworms as commercial silk producers, it is only this cocoon silk that has given any considerable results, the produce of the other glands being far too frail for profitable use. ”

“ It is not, of course, heavy work, but it requires skill and judgment since the many varieties of cocoons need different treatment. Here, for example, are dupions, or double cocoons, which as you doubtless already know have more floss on the outside than do others, and must be well cleaned before any attempt at reeling can be made. Often they cannot be run off at all because the two caterpillars that worked together to make the single cocoon have intertwined the threads until they break all to bits when we try to separate them. ”