^ 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