The Pamphlet Collection of Sir Robert Stout: Volume 84
Part II. — Instructions for Silkworm-Raising
Instructions for Silkworm-Raising.
The purport of this portion of the manual is to give, in a simple and condensed form, the necessary instructions for raising silkworms. Professor Riley, who is perhaps the greatest authority in America on silk culture, in a special report to the United States Department of Agriculture, makes some remarks which apply equally well to New Zealand. He says, "To avoid the disappointment that is sure to follow exaggerated and visionary notions on the subject, it may be well here to emphasize the facts—that the profits of silk culture are always limited; that extensive operations by organized bodies must prove unprofitable where capital finds so many more lucrative fields for employment; that extensive silk-raising is fraught with dangers that do not beset less ambitious operations; that silk culture, in short, is to be recommended only as a light and pleasant employment for those members of the farm or the household who either cannot do or are not engaged in otherwise remunerative work. The greater value of labour here as compared with labour in the older silk-growing countries has been in the past a most serious obstacle; but conditions exist to-day that render this obstacle by no means insuperable. In the first place, comparative prices are often misleading. The girl who makes only 1s. a day in France or Italy does as well as she who earns three or four times as much here, because of the relatively lower prices of all commodities there. Again, the conditions of life are such in those countries that every woman among the agricultural classes finds a profitable avenue for her labour in field and factory, so that the time given to silk-raising must be deducted from other profitable work in which she may be employed. With us, on the contrary, there are thousands and thousands of persons—women, children, page 10 old people—who, from our very condition of life, are unable or unwilling to labour in the field or factory, and have, in short, no opportunities of converting labour into capital. The time that such people might give to silk culture would therefore be pure gain; and in this sense the cheap-labour argument looses all its force. The most serious obstacle to be overcome is the want of a ready market for the cocoons. A permanent market once established the other obstacles will slowly but surely vanish as snow before the coming spring. Silk culture must depend for its growth on the production of cocoons. It will not be safe for individuals to rely on reeling their own silk. The art of reeling in modern filatures, and with steam appliances, has been brought to such perfection that none but skilled reelers can hope to produce a first-class article. Besides, it is difficult to dispose of small parcels of raw silk at satisfactory prices."
Large establishments for rearing silkworms, where as many as 60oz. (2,000,000 worms) were raised in one season, are fast disappearing. The crops now consist of so many thousand small lots raised by a corresponding number of families. To produce a few pounds of cocoons each year does not materially interfere with the household or other duties people may he engaged in, and it is by each household raising a few pounds of cocoons that silk culture must be carried on in this as it is done in other countries.
Professor Riley considers that the following are the most important requisites to successful silkworm culture : (1) Cleanliness; (2) fresh air and as uniform a temperature as possible; (3) plenty of room, so that the worms may not too closely crowd each other; (4) no intermission in the supply of fresh food, except during the moulting periods; (5) uniformity of age in the worms of the same tray, so as to insure their moulting simultaneously; to which might be added, a sufficient number of trees for the supply of leaves.
Definite rules are of little avail, as much depends on circumstances and conditions. Beginners will do well to hatch only a small quantity of eggs. If not successful the first year not much is lost. With a year's experience there will be a better chance of success and of profit the second year.
There is an inclination, among people who are unable to pro- page 11 duce first-class cocoons at the start, to blame the industry if they do not receive what they consider an adequate compensation for the time which they have expended upon the work; and yet these same individuals would not expect to be successful in any other enterprise until they had made themselves thoroughly acquainted by practical experience with the special work involved.
The introduction of silk culture will in time result in a very important yearly revenue, and increase in the public wealth. This, however, may be a less advantage than the fact that, by supplying a new home industry, it would do much towards conserving home tics and interests, and help to strengthen and perpetuate home-living among the people.
The silkworm exists in four states—egg—larva—chrysalis—moth.
Eggs, or graine, or seed.—The eggs are of gray, slate, violet, or dark green colour, according to breed. If unimpregnated (that is, not capable of hatching) or dead they are white or yellowish white. The old Italian and French varieties produce yellow silk, and the Japanese variety, white or greenish silk: these are considered the best. These eggs are covered with a gummy substance, by which they stick on the objects they are laid upon. They are best kept in boxes of perforated tin in a cool, dry, well-ventilated place. Examine them occasionally. If mouldy, brush off and remove at once to a drier place. The temperature should not be above 50° Fahr., but may sink to freezing point without injury. Beware of rats, mice, ants, &c. The eggs remain in a dormant state from seven to nine months. Hatching may be accelerated by heat or retarded by cold. When the trees are well out in leaf the eggs are hatched. By this time they have assumed a slightly lighter colour.
Hatching.—Put the eggs in a room where the temperature is 75° Fahr. Increase the temperature gradually to 80° or, if necessary, to 90°, but not more. In five to eight days, at the latest, the little worms will appear. Do not expose the eggs to the rays of the sun. If they have been wintered adhering to the cloth or paper upon which they were laid they may be hatched on the same; if in loose condition, they must be spread evenly over sheets of paper or cloth. Large quantities are page 12 hatched in an incubator. An incubator may be constructed from pasteboard, in the shape of a box, square or round but tight-fitting, about 2ft. high. Fix a tray near the top made of wire-netting, upon which the cloth or paper with the eggs is laid. Put a small spirit-lamp inside, with a small vessel of water over it, about half way up. But the water must not boil: it is simply put there to create a humid heat, which facilitates the hatching. A thermometer is, as a rule, also fixed inside.
The Larva or Silkworm proper.—The colour of the newly-hatched worms is black or dark grey. They become lighter as they grow older, until the spinning time, when they are of cream white colour. The worm undergoes four moults or sicknesses (casting of the skin). The first moult takes place between the fourth and sixth day after hatching, the second about the tenth, the third about the sixteenth, the fourth about the twenty-fourth day. The periods of sickness last from thirty-six to sixty hours. Thirty-five days after hatching is the normal time for the worms to begin to spin. Just before and after each moult the worms eat voraciously, and between the fourth moult and the time for spinning the quantity of food consumed is surprising.
Any Room or Shed will do to raise silkworms if it is dry and can be thoroughly ventilated. Small quantities can be raised on trays upon tables. The kitchen is a good place. The worms will never leave the trays if properly attended to, that is, if they have a sufficient supply of food, and the temperature is kept even. Large broods are raised on shelves arranged along the walls, or fixed on racks from floor to ceiling, or the trays may be suspended by wires from the ceiling.
Width of Trays 4ft. or 5ft., depth 3in. or 4in., length according to room. Put them 18in. to 2ft. apart. The wood they are made of must be well seasoned, non-resinous, in fact have no smell. The bottom is of wire-netting, cane, or simple slats. The trays must be covered with strong paper. A room 18ft. by 20ft., with two shelves all round, safely accommodates forty thousand worms; that is the issue of one ounce of eggs.
Raising Silkworms.—When the eggs begin to hatch mosquito netting or perforated paper is laid over them. Upon this spread freshly-plucked leaves. The little worms will rise through the meshes or holes and make for the food, when they can be easily page 13 removed to the trays where they are going to be raised. For small broods it is sufficient to put some fresh leaves on the worms. They will crawl on to them, and are then moved. As the worms grow older the size of the meshes of the net or the holes of the paper has to be increased. They have to be moved on clean paper for the purpose of cleaning the trays (removing the litter). The smell of decayed and fermenting leaves is injurious to them—in fact, they dislike all bad smells. Coarse twine netting may be used for the same purpose. Each day's hatching should be kept separate, so that the worms go through different moultings with uniformity. Any eggs not hatched after the fourth day (after hatching began), are not worth keeping. They contain inferior worms, and are best thrown away.
Feeding.—It is recommended by some that the leaves be hashed, that is, minced with a knife like you would prepare lettuce for salad. This is advisable if they are old, but it is not necessary if the hatching takes place when the leaves are still young and tender. With small broods it may be done during the first two ages, but it is not necessary after the second moult. Besides giving a lot of trouble, hashed leaves dry quicker, and the food has to be renewed oftener.
As to the number of times of feeding, practical experience alone will teach how to proceed. The food should be renewed whenever the preceding supply has been devoured or become dry. During the last two stages as a rule six meals are given, with one substantial one late at night, and another the first thing in the morning.
I would strongly recommend to use only mulberry leaves, and rather decrease the number of worms than use other food.
Never feed with wet, soiled, withered, or partly-decayed leaves; they breed disease.
Spread leaves evenly, so that all may feed alike.
If wet, shake them in a cloth. As rain is very frequent in most parts of New Zealand it would be advisable to pick a day's supply of leaves beforehand, and keep them in a cool place.
Leaves are, as a rule, stripped from the trees. Some people cut branches off, and so prune the trees at the same time.
The temperature should always be kept between 70° and 80° Fahr. Keep it as even as possible during the moulting periods. page 14 With a high and even temperature, say, 75°, the worms will enjoy excellent health and appetite, and consequently make more silk. During the daytime, when the temperature outside is about 70° or more, the windows may be kept open; but the worms must not be exposed to the rays of the sun.
Moulting.—The worms leave off eating, and feeding should cease. Some will moult much quicker than others; but they may be left half a day without food, so as to wait until the majority have cast their skins. There will nearly always he a few which remain sick after the others have started feeding again. If they appear weak and languid destroy them; they would only contaminate the others. If they are only smaller in size, but otherwise healthy and vigorous, keep them separate, or the batch will grow more and more irregular. They may be moved with a quill pen; but it is better to touch silk worms as little as possible.
The importance of keeping each batch together and so causing the worms to moult at the same time cannot be too much insisted upon. When the moult is completed, feed copiously. They grow rapidly after each moult. When too crowded divide the batch.
The fourth moult is the most critical. Afterwards they will eat for about ten days longer, and the litter should be often removed during this period. They will eat ravenously about the thirtieth day, but leave off gradually, decrease somewhat in size, become nearly transparent, and sway their heads to and fro in search of something. Now they are ready to spin.
Spinning.—Arches of broom, corn, or brush must be prepared. They should interlock, and be about 12in. to 18in. high. Some people use a cocooning ladder made of lattice-work, others put wood shavings on the trays, or paper tubes. The brush must be dry, and have no smell.
The temperature should be kept about 75° to 80°. The worms will mount immediately into the branches and begin to spin. A few may not mount. Put some brush for these on the trays. Allow plenty of room, so as to prevent two worms joining and forming only one cocoon. These double cocoons have a much lower market value. Before the worms spin they emit a dirty fluid, which stains and injures cocoons on which it might page 15 drop. This will occur seldom if they have plenty of room and start spinning about the same time. In about eight or ten days the cocoon will he finished, and the worm inside has reached the third or chrysalis state. A rattling sound is heard if the cocoon is shaken; but, to make quite sure, the best plan is to cut a few cocoons with a knife.
Cocoon.—The cocoon consists of an outer lining of loose, woolly silk called " floss silk," and an inner part, "the pod," which should he strong and compact, composed of a firm continuous thread. This is the part used for reeling, and upon its consistency (quantity of silk) and the fineness and gloss of its texture depends the commercial value of the cocoon.
The Chrysalis requires no special description. It makes excellent manure. The chrysalis state lasts from twelve to twenty days, when the skin bursts, and the moth emerges.
After about eight days from the time spinning commenced the cocoons may be gathered, and are now ready for the market. Where reeling establishments are at hand the cocoons may be delivered at once, after the floss silk has been taken off. In New Zealand (there being no filatures as yet) it will be better to choke the chrysalis and dry the cocoons. Their weight will decrease about 60 per cent., but their price will increase in exact proportion—that is, 31b. become 11b.; but it is the chrysalis which dries and causes the decrease of weight, and not the silk. Cocoons with the grubs dried are called "dry cocoons," the others "fresh cocoons."
Some people having hand-reels might choose to reel their cocoons. To these I would recommend not to reel only one cocoon at a time, as such silk is not marketable. Raw silk consists of the threads of from three to six cocoons combined in one, according to the different sizes required in the market. Italian and French reelers have acquired perfection, and we cannot compete, for various reasons. But persons reeling for amusement might make excellent fishing-lines.
Choking the Chrysalis.—All cocoons which are not intended for reproduction (about which later on) must undergo the process of having the grubs killed, otherwise all the moths would in course of time work their way out of the cocoons. Such cocoons—pierced cocoons—cannot be reeled, but have to be carded like cotton or wool. They are of little value.page 16
Cocoons may be choked by dry heat or by steaming. Put them in an oven with a temperature of about 150° Fahr. Two hours will suffice. By this method the silk is often burned, if not carefully looked after. Where facilities are at hand steaming is by far the better and surer method. Put the cocoons in a tightly-fitting box, make a hole, and turn the steam in. Half an hour will do it. For small quantities it is recommended to put them in shallow baskets or boxes and expose them to the rays of the sun for two or three days; cover with glass panes, and leave a small opening for moisture to evaporate. Cessation of a certain humming noise is an indication of the chrysalis being dead; but the surest way of ascertaining the fact is again to cut a few cocoons and examine the chrysalis by pricking it with a pin.
This operation completed, the cocoons are put again on shelves, not more than 3in. deep, and left to dry. Plenty of air should be admitted, and the cocoons frequently stirred. After this they may be kept for any length of time, but they are still liable to attacks from rats and mice.
Selecting Cocoons for Reproduction.—Those people who intend to raise silkworm eggs for the next season will have to make provision accordingly. When the cocoons are taken from the bush the largest and firmest should be selected for breeding purposes. Double cocoons must not be used. They are recognizable by their extraordinary size and unusual shape. Soiled cocoons, if large and firm, may be used. Take, say, fifty cocoons, half males, half females (more or less), which will produce about ten thousand eggs. Male cocoons are, as a rule, constricted in the middle; female cocoons are not, but more round, and rather larger. However, it is not always safe to go by this rule. A safer method seems the following, recommended by Riley :Weigh a hundred cocoons, and strike the average : all above the average will be found to be females. Paste these selected cocoons on paper or cloth, and in from twelve to twenty days the moth will have worked itself out of the cocoon.
The Moth.—The fourth and last state of the silkworm. The moth emits a strong fluid, which moistens the end of the cocoon, and dissolves the gummy lining. Then the moth emerges. The moth is of cream colour. Neither sex flies, but the males flutter page 17 continually with their wings. Females have larger bodies than males. They issue mostly early in the morning, and couple soon afterwards.
Egg-laying, or Reproduction.—Keep the room dark. If necessary, place sexes together. Destroy all that are deformed. Should more males issue the first day than females, keep them in a box until the next day, when the reverse may be the case. Strong males may be used twice. They should remain together six to eight hours. If not uncoupled after twelve hours, separate them. Handle them gently, by getting hold of their wings and bringing their heads together. The males may be thrown away when all the females have been impregnated. Put the females on blotting-paper first, where they will discharge a yellowish fluid. From there put them on woollen or linen stuff or paper (in a slightly-slanting position), where the moth will lay her eggs (300 to 400). They are laid very regularly, as the moth very seldom leaves the spot. After two days the moth is removed, as all eggs worth having will be laid by that time.
Let the eggs dry, and after a week they may be stored away in a cool, dry place until the following season. They are best kept on the cloths they were laid upon. When deposited the eggs are yellow, and this colour they retain if unimpregnated; otherwise they assume a darker colour, and become indented. The female moths may be thrown away also.
In Italy and France the female moths are kept for the purpose of microscopical examination, so as to ascertain whether the eggs are healthy or not. Silk culture is in its infancy yet in New Zealand, and I am not aware of any diseases having shown themselves in the few cases where people have raised silkworm eggs. I refrain, therefore, from giving a description of those terrible diseases which made their first appearance in Europe about twenty years ago, and nearly ruined the industry, but which, thanks, chiefly, to the researches of Pasteur, were successfully combated. I sincerely trust I shall never have occasion to refer to them as existing in New Zealand.page 18
|First day to fifth||75°||to 80° Fahr.||9lb. leaves.||12 sq. ft.|
|Seventh day to tenth||72° to 75 Fahr.||24lb. leaves.||24 sq. ft.|
|Eleventh day to sixteenth||72° to 75° Fahr.||80lb. leaves.||60 sq. ft.|
|Seventeenth day to twenty-third||72° to 75° Fahr.||260lb. leaves.||140 sq. ft.|
|Twenty-fourth day to twenty-eighth||75°||Fahr.||1,000lb||350 sq. ft.|
|Twenty-ninth day to thirty-fifth||75°||Fahr.||1,000lb||600 sq. ft.|
- After first moult;
- Between second and third moult, once or twice;
- Between third and fourth moult, twice;
- After fourth moult, three or four times.
|First age||81b.||10 square feet.|
|Second age||24lb.||30 square feet.|
|Third age||65lb.||50-75 square feet.|
|Fourth age||200lb.||100—160 square feet.|
|Fifth age||1,200lb.||320 square feet.|
|Fifth age||1,200lb.||430—640 square feet.|
These figures are based on practical experience in Italy and the United States. Raisers will, however, do well to be guided by their own common-sense and observations as to renewal of food and increase of accommodation.
Average number of eggs per ounce, 37,000 to 40,000.
Average number of fresh cocoons per lb., 300 to 400.
Maximum amount of fresh cocoons from loz. of eggs, 1501b.
Average amount of fresh cocoons from loz. of eggs, 801b. to 1001b.
Two adults can easily take charge of 2oz., or 80,000 worms.
31b. to 3½b. of fresh cocoons equal to 1lb. dry cocoons.
One moth lays three to four hundred eggs.
3½b. to 4lb. of dry cocoons make 1lb. raw silk.page 19
101b. to 121b. of fresh cocoons make 1lb. raw silk.
Length of thread from one cocoon, 800 to 1,500 yards, according to breed.
Temperature in Auckland during October, November, and December; and Rainfall.
By Authority: George Didsbury, Government Printer, Wellington.—1886.