^ 5J UNIVERSITY OF CALIFORNIA Agricultural Experiment Station COLLEGE OF AGRICULTURE E, W. HILGARD, DIRECTOR BERKELEY, CALIFORNIA CIRCULAR No. 12. (June, 1904.) SILK CULTURE, By C. W. WOODWORTH. The rearing of silkworms has been practiced on a small scale in California for many years, and it may be considered amply demon- strated that they do well in nearly every part of the State. The busi- ness had one brief period of success when there was a demand in Europe for California-grown silkworm eggs, but never has been profitable for silk production. The reason usually assigned for this failure is the cost of labor here compared with that in other lands. This high cost of labor does not apply simply to the actual rearing of the worms, but also to the manu- facturing process, called reeling, w^hereby the silk is taken from the cocoons and made into the product known as raw silk. There would be no difficulty in this State in obtaining skilled oper- atives either with Oriental or with European experience in silk reeling, but they would command very much higher wages than they receive in their native country for the same work. This difference must be taken from the price that is paid for cocoons, since raw silk is imported duty free. Notwithstanding this very evident handicap of the American silk-pro- ducer, there is a continual demand for information by those desiring to enter into the business. This circular is issued by the Station for the information of its correspondents. The Station is experimenting with silk culture in a small way, in the hope that the labor item might in some manner be reduced enough to make the industry profitable, but with no prospect of immediate results. The Egg. — Silkworms are usually purchased during the winter in the egg condition. They may be imported from France or Italy, and sometimes come from China or Japan. These imported eggs occasion- ally hatch in transit and die, or may be so far advanced in their develop- ment that they hatch before the mulberry is in foliage. The latter contingency can be met by placing the eggs in a fruit-jar and keeping this on ice without any very evident deterioration in the vitality of the worms when they are finally brought forth. — 2 — The approach of the hatching period is observable in the change of color of the egg to a light-bluish shade, which gives ample warning. If silk culture were profitable in this country, as it is in Europe, there would soon be an abundance of locally-grown eggs produced by experts in that business. The importance of careful selection, par- ticularly to insure healthy eggs, is so great that growers would prefer to buy their eggs each year, just as we purchase garden seeds instead of growing them; but under the present conditions each silk-raiser should produce his own eggs. It is customary in silk-growing countries to observe great care in wintering the eggs, so that they will not be prematurely developed. They may be kept at a nearly freezing temperature until about eighteen days before the time they are desired to hatch, and the temperature raised gradually from day to day and kept uniform, not going above 75 degrees. This results in a very regular development and the hatching of the eggs pretty much all at one time, which is a great convenience in subsequent work. Growth of the Worms. — The eggs of silkworms are considerably less than a sixteenth of an inch in diameter, varying somewhat with the variety, and requiring about forty thousand to weigh an ounce. The young worm is only about two thirds the weight of the egg from which it hatches, the other third being the weight of the shell. In about a month the worms increase in size until they weigh nearly an ounce apiece and are some three and a half inches long. During this time they change their skin four times. These changes are called molts. Just before the molt the worm spins a larger amount of silk than usual, making a carpet into which it tangles its claws so that they will hold fast as it crawls out of its skin. During the molting period no food is taken, and if the worm is diseased it will often fail to accom- plish the change, but die and dry up. There is always liable to be more or less loss at molting time; at least, when worms are grown in large numbers. Feeding the Worms.— li only a few worms are kept together they will usually come to maturity with scarcely any loss with almost any kind of treatment, just so long as they have food enough. When silk- worms are grown on a commercial scale, however, it becomes more necessary to feed them according to a definite system and to give them the best of care. The usual practice is to give the worms chopped leaves during the first two stages, and whole leaves the rest of their life. The feeding table here presented is based upon the best European practice, and will exhibit in a very compact form the detail of this operation. The ages given in the first column represent th^ inte^'val beb^'^en the »3^ molts; the increase in quarters is given to the worms at the time they complete the molting process and again in the middle of the first two ages. The column giving the number of worms in a square inch or square centimeter is given to enable the silk-raiser to determine rapidly how much too thick the worms may be in any particular place, so as to assist in more uniform distribution. The number of meals a day and the ration at each meal, of course, will vary to some slight extent according to the needs of the worms. When it is warmer they may require more, and when it is cooler less, than the amounts given in the table. The optimum temperature is usually placed at 72 degrees Fahrenheit, and the table will give approximately that which is re- quired under this temperature. If the temperature is a little higher they may come to maturity a little quicker than is indicated, and if cooler will require distinctly longer. Feeding Table for One Ounce of Eggs, 40,000 Worms. Age. Quarters. No. Worms. Day. No. Meals. Ration per Meal. Per sq. in. Sq. yd. = tV sq. cm. Chopped leaves, ozs. Hatching. ( 1 8 2 f 1 32 1 2 10 2 j 1 3 10 3 First Age- - 1 4 10 4 I 2 16 - 5 8 5 6 6 5 First Molt. f 4 8 7 ■ 8 8 8 10 12 Second Age <j 1 I 8 4 J 9 10 7 5 20 25 Whole leaves, Second Molt. Per sq. cm. lbs. = ^ sq. ft. 12 7 2 7 3 Third Age. 16 32 iis 7 5 1 14 6 5 115 4 5 Third Molt. ri6 6 6 17 6 8 . 18 119 6 10 Fourth Age 32 16 6 15 20 6 12 121 6 12 Fourth Molt. '22 23 24 25 4 5 6 7 25 25 25 25 Fifth Age-- 64 8 ■ 26 27 28 29 30 8 8 8 8 7 25 30 30 28 28 Spinning. — 4 — Care of the Worms.— Silkworms are very subject to disease, especially when grown in large numbers, and to prevent this the silk-raiser must exercise the utmost care, particularly in the removal of the droppings of the worms and of the uneaten remains of the food. Neglect in these matters will usually result in the starting of an epidemic among the worms, showing itself at each molt, but most fatally just as the worms are about ready to spin. If the conditions are not maintained abso- lutely sanitary it is not infrequent to lose from fift}^ to seventy-five per cent of the worms just as they are about to undertake their labors of silk production. There are quite a number of silkworm diseases recognized by silk-growers, some of which are hereditary, and may destroy the worms in spite of the best of care. Very commonly the loss with amateurs, however, is entirely preventable, and represents simply the carelessness of the grower. The means of cleaning the trays used for silkworms is the use of mosquito net during the first two stages, and a coarse string net when the insects are larger ; or perforated paper has proven very satisfactory where it can be obtained. The net is laid over the worms just before feeding, and they will crawl through, leaving the old leaves, which can then be removed. It is a good plan to change them at least once a day, and if the weather is moist the use of disinfectants in the room and about the trays is certainly to be approved. The nets used in changing the food should be, under any condition, treated from time to time with antiseptics. Good ventilation should be provided to decrease the liability of excessive moisture, which is one of the conditions under which diseases most readily develop. Spinning. — When the insects are fully fed they begin to wander about, cease to feed, and become much more transparent in appearance. These are indications of the approach of the spinning time. They must now be provided with places for spinning their cocoons. The practice in Europe is to furnish them with brush cut in the winter from trees and bound together in such a way that they may be set upon the trays in rows, spreading out hedgelike at the top. The worms climb up into these hedges and spin their cocoons between the twigs. A very satis- factory arrangement can be made of lath by laying them edge-wise about three fourths of an inch apart and tacking other laths at right angles across these to hold them in position. Gathering and Marketing Cocoons.— Ahout three days after spinning, the cocoons should be gathered. While gathering cocoons one should sort them at the same time, keeping the perfectly clean ones by them- selves. Those that are stained or thin hardly pay to care for and will ordinarily be destroyed. Those that are only slightly spotted may, however, be sold at a lower rate than the good cocoons and may perhaps pay to ship. In picking cocoons care should be taken to remove all litter from each cocoon before it is placed with the rest. To prepare for shipping it is necessary to remove all loose floss silk, as it is called. This has a market value almost equal weight for weight with the cocoons, and should be cared for accordingly. Finally, before cocoons are sent to the market it is necessary, unless one is very close to a reeling factory, to kill the insect within. This can be very satisfac- torily accomplished by drying the cocoons in the sun on trays, much as fruit is handled ; or they may be killed by exposing them to more intense heat, as by the use of steam under pressure, or by baking them in an oven, taking care to prevent burning. A method more convenient than any of these is the use of carbon bisulfid. If the cocoons are placed in a tight box and a saucer laid on top in which a little carbon bisulfid is poured and the box closed tightly for twelve hours the insects will be killed by the gas produced. Use about two ounces of carbon bisulfid for one hundred pounds of cocoons. In using this gas it should be remembered that it is very explosive and that a light should not be brought near the box. After killing it is necessary to dry the cocoons to prevent molding. For this purpose they can be spread out on the floor from two to three inches thick, and they will dry in a few days, when they will keep indefinitely. In packing them for shipment prob- ably the best method is to sack them in light cotton sacks, or they may be crated and shipped in that form. The Department of Agriculture at Washington has been purchasing silk for reeling purposes and probably would take all that may be produced for some time to come. Egg-Baising.—¥ or the present it will be desirable for every grower to raise his own eggs. Great care should be exercised in choosing cocoons for breeding purposes. One should take those that are large in size, of the typical shape of the race he is growing, and particularly those that are firm, indicating large quantities of silk. Select several times as many as you desire to hatch, then determine by weighing those that are above and below the average weight, which will approximately divide them according to their sex, the males being smaller. Now select from one hundred to one hundred and fifty cocoons of each sex for each ounce of eggs it is desired to produce. These selected cocoons are commonly strung on a thread, catching the needle through the floss silk only, and hung up until the moths emerge, which will take about ten days after spinning. The moths will emerge mostly early in the morning. The sexes should be kept apart until the wings are fully expanded, say until eight or nine o'clock; equal numbers of each sex should now be placed together in a darkened room, and visited from time to time to see that they do not become unpaired. About three o'clock in the — 6 — afternoon they must be separated, which may be done by grasping the female by the wings and the male by the abdomen, squeezing the latter gently and at the same time pulling them apart. The males may now be thrown away and the females placed on blotting paper, where they will exude a yellow liquid, and then they are ready to begin laying their eggs. We prefer the Japanese method of separating each moth by confining her within a small area, which can be done by making' cylinders of glazed paper. The Japanese use sections of large bamboo, like napkin rings. In this way it is possible to keep the laying of each moth by itself, and if everything does not progress normally the whole layings of the moths giving imperfect eggs can be destroyed. Profes- sional egg-raisers always examine the interior of the moth under the microscope to determine the presence of certain hereditary diseases, but this is a matter which the ordinary grower will not be able to do : still, by having the eggs of each moth separate one can avoid those worst affected by saving only those which change their color normally, showing a healthy development. Profit in Silk-Raising.— MsLiiy people have gone into silk-raising with very much exaggerated ideas as to the profits of the business, and usually are thoroughly disappointed with the outcome of the first year's, work. Under ordinary circumstances one can not expect to obtain even fair wages for the time employed in producing the silk, and if one is unfortunate in the matter of diseases he may obtain absolutely no income for his work. Under favorable conditions one could expect to obtain about one hundred pounds of fresh cocoons, or perhaps thirty- three pounds dried ready for shipment from an ounce of eggs. These are worth between $25 and $30, varying according to the price of silk. One person can not expect to care for more than two ounces of eggs, for while this amount would not require all his time during the first two ages, it would keep him very busy during the last age. Counting the preliminary preparation and the shipping of the cocoons, this would involve about six weeks' work, and after deducting the cost of the plant there is no very large amount left for wages. This incom•'^ of course, is only possible when one gives the best of. attention to the insects and brings them to perfection with very little loss. There is the possibility, however, that a better showing might be made by hatching the insects at intervals and in smaller numbers so as to extend the feeding period through the larger part of the summer and make the business fairly profitable, providing one has an abundance of mul- berry trees to furnish food for the worms. Digitized by the Internet Archive in 2012 with funding from University of California, Davis Libraries http://www.archive.org/details/essentialsofsoci12cros