UNIVERSITY OF CALIFORNIA AGRICULTURAL EXPERIMENT STATION 
 COLLEGE OF AGRICULTURE benj. ide wheeler, president 
 
 THOMAS FORSYTH HUNT, Dean and Director 
 
 BERKELEY h. e. van norman, vice-director and dean 
 
 University Farm School 
 
 CIRCULAR No. 116 
 
 (March, 1914) 
 
 SILK WORM EXPERIMENTS 
 
 BY 
 C. W. WOODWORTH 
 
 The Agricultural Experiment Station will send a small quantity 
 of silkworm eggs free of charge to any one willing to co-operate with 
 it in its effort to make silk culture profitable in California. 
 
 A large number of eggs of all the leading races of silkworms from 
 various countries where the silk is grown commercially, in Europe and 
 Asia, have been secured and we desire to interest as large a number 
 of persons as possible. 
 
 Thus far the growing of silk has been unprofitable in this state. 
 The reason it has not developed here is strictly because of our economic 
 conditions. The climate in many parts of the state is ideal and silk- 
 worms have been grown here every year in small quantities for more 
 than a generation. As long as the profits from other industries are 
 larger than those secured in growing silk, this industry cannot thrive 
 and should not be encouraged. 
 
 Neither the price of silk nor the cost of labor are liable to change 
 enough in the near future to render the growing of silk profitable in 
 this state if carried on in the usual manner. 
 
 The present experiment. — There is, however, a possibility that the 
 cost of production can be diminished as has been done in recent years 
 in the case of many other agricultural crops. The use of a cheaper 
 food, or the employment of less expensive methods of handling the 
 worms, may, either of them, be sufficient to place the industry on a 
 sound financial basis. 
 
 We are soliciting co-operation in the attempt to solve the first of 
 these problems, the securing of cheaper food, by testing as great a 
 range of food plants as possible. We propose to endeavor to develop 
 silkworms that will thrive on some plant producing more tons of leaves 
 to the acre and one cheaper to harvest than the mulberry, which has 
 hitherto been exclusively employed in silk production. 
 
The production of such a race will require the breeding together 
 of individuals that have less strongly developed the natural repug- 
 nance to other kinds of foliage until, finally, if successful, a breed is 
 evolved which will thrive upon some satisfactory forage crop. 
 
 We have secured as great a variety of races of silkworms as we 
 could, and will test as large a variety of plants as possible, so as to 
 have a great abundance of individuals with diverse food reactions 
 from which to select in making our matings. The greater this variety 
 (and if many co-operate this can be very large) the more probable it 
 would seem that satisfactory races would arise. 
 
 How to conduct the experiment. — The care of silkworms is a very 
 simple process that anyone can perform; indeed, in most countries a 
 large proportion of the work is done by children. When only a few 
 are kept together, practically all the directions that are necessary is 
 that they be kept supplied with fresh food, and that which is not 
 eaten be removed if it does not dry up completely, since the litter 
 should not be permitted to become moldy. 
 
 The testing of various food plants consists simply in offering them 
 a meal of one kind of leaf and then another, but alternating with 
 mulberry or other known food plant so that the worms will not suffer 
 for lack of food, and finally when something is found that they will 
 relish they may be limited to that food and reared to maturity upon it. 
 
 While the mulberry is the only leaf used in Europe and Asia for 
 the production of silk, osage orange has been similarly employed in 
 the Mississippi Valley on a small scale, producing silk equal in every 
 respect to that grown on mulberry, and silkworms have often been 
 fed on lettuce for a portion or even the whole of their lives. More 
 than a hundred years ago English investigators had succeeded in 
 rearing them on quite a variety of plants, including blackberry, elm, 
 sweet cowslip, primrose, spinach, and viper grass. 
 
 There is much difference in their acceptance of lettuce as a food, 
 as shown by different races. We have already this year had worms 
 of three races starve, while those of two other races eat this leaf 
 greedily, and we have had similar experiences in other years. Tem- 
 perature has been observed to have great influence, caterpillars accept- 
 ing unusual food much more readily when they are kept in a warm 
 room. The condition of the leaf also has an effect, the young and 
 tender leaves being more freely eaten. The age of the insect makes a 
 striking difference, the older insect becoming less particular as to the 
 character of the food. All of these facts may be of importance in 
 our task of overcoming the present natural instinct of this insect. 
 
Those who accept the eggs will be expected to do the following : 
 
 ( 1 ) Endeavor to feed the worms on some other kind of leaves than 
 mulberry. 
 
 (2) Keep a record of the foods tried. 
 
 (3) Return to us, say, half of the cocoons as soon as spun, together 
 with a record of their feeding, so that we can use the moths produced 
 in our breeding experiments. 
 
 After these lay, we will be glad to return to those co-operating 
 with us a larger quantity of eggs for their next season's rearing from 
 these especially selected moths. 
 
 How to obtain the eggs. — Send a card addressed to Professor C. W. 
 Woodworth, University of California, Berkeley, CaL, asking that eggs 
 be reserved for you, giving your postoffice address. 
 
 The eggs are now held in cold storage and will not be shipped 
 until the mulberries come into leaf, but the sending of a card at this 
 time will insure that eggs will be reserved for you. 
 
 Ordinarily only a single lot of about a hundred eggs will be sent 
 to one address; however, anyone who is prepared to co-operate on a 
 larger scale may receive more than one lot. Teachers may arrange, 
 for instance, for a lot for each pupil by agreeing to take general 
 charge of the whole set of experiments and to see that the cocoons are 
 promptly sent in for our breeding work. 
 
 Feeding the worms — The usual practice is to give the worms 
 chopped leaves during the first two stages, and whole leaves the rest 
 of their life. The number of meals a day and the rations 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 food, and when 
 it is cooler less. The optimum temperature is usually placed at 72 
 degrees Fahrenheit. If the temperature is a little higher, they may 
 come to maturity a little more quickly, and if it is lower, they will 
 take distinctly longer to mature. 
 
 Care of the worms. — Silkworms are very subject to disease, espec- 
 ially when grown in large numbers, and to prevent this the silk-raisers 
 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 usually results 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 absolutely sanitary 'it is not infrequent to lose from 50 to 
 75 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 ob- 
 tained. 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 ex- 
 cessive 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 satisfactory arrangement can be made of lath by 
 laying them edgewise about three-fourths of an inch apart and tacking 
 other laths at right angles across these to hold them in position.