Chapter 8 RAISING SILKWORMS

Although silkworms are not actually reared in the open air, there is so much outdoor work and moderate exercise connected with their care that the subject may properly be included in a book on outdoor work.

The best food for silkworms is the leaf of the white mulberry. If you have already a hedge of this or several trees you can begin at once. If not, several years must elapse while you raise your preliminary crop of mulberry trees from seeds or cuttings. It is useless to buy silkworm eggs if you have not the wherewithal to feed your infant caterpillars. You may not think of going into silkworm rearing in a commercial way but only as an interesting bit of nature study. Why not make up some neat attractive cases, each containing a little collection illustrating the four stages of the growth of this insect? Heat a few eggs to destroy life, then glue them to a card; preserve a caterpillar in a vial of alcohol; glue a cocoon to a card; pin and spread two of the moths, a male and a female, and pin them into the box. From such a box school children will get a far more definite idea of insect metamorphosis than they will ever get from a book on zo?logy. Such little collections ought to sell well in schools where nature study, zo?logy, or agriculture is taught.

The mulberry silkworm makes the best silk, although it is by no means the only silk-spinning insect. Every now and then we read of some one who is experimenting with the silk of our American or giant silkworms, the Promethea or the Cecropia, or with the silk spun by spiders. But none as yet compares with Bombyx mori in either quantity or quality of its product or in ease of rearing or in reeling of the silk.

The adult moth lays between three and seven hundred eggs during the first three days after she emerges from her cocoon. In a week or ten days she dies, her work finished. Moths in the wild state are at some pains to deposit their eggs on the favourite food plant of their young, but in the case of Bombyx mori this instinct has been lost in the countless years of domestication. The eggs, when laid, are moist with a sort of glue which secures them to the surface upon which they are deposited. The winter is passed in the egg stage. A cool, dry place is safest for them, where no sudden changes of temperature are possible. A steady temperature of thirty-five degrees is ideal, and they must be enclosed in something that is mouse proof, though not air-tight. A perforated tin box is right for this purpose. Silkworm eggs for study may be obtained from dealers in miscellaneous insects, birds, animals, etc.

As spring approaches you must watch the mulberry leaves and make your preparations. Any room in which temperature and ventilation can be regulated will serve for rearing silkworms. You should have some racks made of lattice work, and shelves, open to the air, on which to place them. I have seen a clothes-horse, with racks resting upon the rungs, used for this. A supply of cheap wrapping paper or newspapers should be on hand to put on the shelves, and some coarse netting, the use of which will be described later. Do not make the mistake of getting too many eggs. An ounce does not seem like very much, but the well-grown worms from an ounce of eggs ought to have at least seventy-five square yards of shelf space. They will require during the first six days only eleven pounds of leaves, six meals a day, but during the eight days just before spinning they will require over half a ton of food. Imagine lugging in two hundred weight of fresh mulberry leaves five times a day to feed these ravenous things so dependent upon you!

Movable frame and light shelves for feeding silkworms

Warmth and moisture are required for hatching the eggs. As the spring advances and the mulberry shows signs of putting forth its leaves, the silkworm eggs should be spread thinly on sheets of paper on the shelves in a temperature of about fifty-five degrees Fahr. The temperature should be increased after three or four days and gradually raised to seventy-three degrees Fahr. Sprinkle the floor to make the air moist, but do not wet the eggs. At this temperature hatching will take place after about ten days' time. Watch the eggs. When they begin to whiten you must get to work, as the first worms will soon be out. Take two thicknesses of coarse tulle or bobinet cut the size of the racks. Chop some young, tender mulberry leaves very fine. Scatter a thin layer of these bits over the cloth and lightly lay it over the hatching eggs. No sooner do the young silkworms become aware of the presence of their favourite vegetable than they make their way to it, coming up through the holes of the bobinet as easily as "rolling off a log." They are tiny creatures. Eight of them laid end to end would hardly measure an inch. As hatching usually takes place in the morning, by ten o'clock the worms will all have crawled through the netting to the leaves on the upper layer of the net. This can now be transferred to the rearing shelf. The netting should be kept well stretched, as the worms may be injured if buried down amongst the leaf bits. All through life silkworms must be handled with extreme care. If necessary to lift any individual from one shelf to another it should be done with tenderest touch. Rough treatment is fatal.

A clothes-horse fitted with racks for feeding silkworms

For young worms the newly opened leaves are the best. As they grow older their tastes change and the more mature leaves may be given. A quantity of leaves may be gathered at one time and kept fresh. The leaves themselves should never be put into water. Prepare the food by removing the foliage you intend to feed from the stems. Then chop or cut it into fine shreds. Six times a day a small quantity of the prepared leaf should be sprinkled lightly over the netting.

Like other caterpillars, silkworms shed their skins at certain intervals. The six-day period between hatching and the first moult is called "the first age." On the fourth day it is best to change the beds, as the droppings from the worms and the litter of uneaten leaves are not healthy for the moulting caterpillars. Spread fresh leaves on nets and place over the worms in the evening. By morning all will be ready for the clean shelf and doubled space. As the sixth day approaches, the worms lose appetite and cease to move about. Finally the skin whitens, the head seems to grow larger, and each little creature pulls himself out of his old skin and finds himself clad in a new suit. I imagine he must feel very much as a boy does when on the first really warm day in April his mother allows him to shed his winter underwear, get his hair cut short, and wear his summer blouse and knickers.

The young worm, however, does not feel very lively at first. No food should be given for several hours. When signs of waking are evident, food should be given and the worms transferred to clean shelves by means of the nets. On the third day they should be changed to fresh papers. Four meals a day are needed by the caterpillars at this time. The second age is shorter than the first, being only four or five days. The skin now changes in colour from gray to yellowish white. After the second moult their food need not be cut much, but they require a lot of it, as they should double their size during the third age, which lasts six or seven days. If the weather is pretty warm their development is faster. They should never be crowded nor allowed to go hungry. Always change to clean shelves when the dead leaves and excrement become the least offensive. This odour, which you can escape by leaving the room, may be deadly to your pets. They are helpless to escape it, and are entirely at your mercy.

During the fourth age, i. e., after the third moult, give more space and feed small branches with leaves on. Always remove every berry from the mulberry branches or the worms will eat them and be made sick. Their appetites are enormous, their growth rapid. Change the beds four times during this period of nine days.

A rack or ladder for silkworms to spin on

After the fourth moult the worms pass into the last age. Five or six days of voracious feeding brings them near that most dramatic event in their lives-the cocoon spinning. For three days, now, instead of eating steadily they wander aimlessly about, as if seeking they know not what; they wag their heads; they behave in an altogether restless and uncertain way. Is it some mortal ailment or mere "weakness of intellect?" You are expecting this and have prepared for it beforehand. They will not need to search long for a place to mount and spin in safety and security their cocoon of shining silvery silk. Farmers' Bulletin, No. 165, recommends the use of small, clean, leafless brush tied together into bundles and fastened between the shelves in rows a foot or so apart. Some use a sort of rack or ladder of narrow strips of wood which should be placed upright on the shelf where the worms can easily find it. They spin between the slats. Any worms which seem not to be ready to spin with the others should be fed until they, too, feel the impulse to travel.

As the process of spinning takes some hours, there will be no difficulty in observing it from start to finish. You are entitled to this exhibition, for, without your constant care and feeding, these creatures would not have been able to develop. The dull, inactive silkworm has acquired wonderful agility, and without practice is able to weave himself into his sleeping bag with astonishing celerity, reeling out his twelve hundred or sixteen hundred yards of silk in one continuous thread. There are no knots or kinks in it. It is inaccurate as well as rather silly to refer to the cocoon as a shroud or burial casket, as some do. The creature inside is just as much alive as ever it was.

The cocoons with the live pup? inside are called green cocoons. To prepare them for market they are usually subjected to heat either in the oven or by steaming. No water should touch the cocoons, neither should the oven be hot enough to brown them. After heating they should be dried in the sun or other heat. Open one when you think they may be dry; if they are, the pup? inside can be rubbed into powder with the fingers. A good price per pound is paid for dried cocoons, but it takes five hundred or more to weigh a pound.

If you have never seen a moth emerge from its cocoon you should keep several of your cocoons. In eighteen or twenty days the moth comes out, usually in early morning. Invite your friends to have a look, too. Must the moth break the threads in getting out, or is the cocoon woven in a manner to provide a gateway when it shall be needed? How does the creature get out anyway, and what is it like when it first arrives in the open? Wonderful happenings must have been going on inside to make a winged moth out of that naked caterpillar. Something left in the cocoon rattles when you shake it. Examine the dried ball and you will recognize in it the cast-off clothes, hat, coat, socks, and boots that he had on when he shut himself in. There, too, is the brown shell he wore as a pupa. You may think you know these things by reading about them, but you do not, really. Hearsay is not the real thing in any realm of life, least of all in the realm of nature.

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