Silk is undisputedly the most beautiful of all natural fibres, with its unearthly sheen. It is also uncommonly strong, even at its finest, when it is almost invisible. And unlike all other fibres used to make fabrics, it is spun out by a humble caterpillar that grows to perhaps the size of a woman's smallest finger, known scientifically as Bombyx mori, or perhaps by one of the cultivated silkworm's less familiar cousins.
Since mankind discovered the wonder of the silkworm's floss, it has been used for the costliest of garments. It has been the cause of espionage, murder, and wars. Silken fabrics have traveled for thousands of miles from their origins at a time when few people traveled more than a hundred miles from their birthplaces in their entire lives. It would seem that such a fibre must be incredibly difficult to cultivate, but it is not. It IS a time-consuming process, for every step must be done carefully and by hand, and growing the silkworms to the cocoon stage is only half the process. After the cocoon is formed, the silk must be cleaned and processed, into either filament or spun silk thread. It is then dyed to the desired colour or allowed to stay a pristine white, and can be used for a myriad of different purposed, from fine cords to delicate tabletweavings and lush fabrics.
The process of growing silkworms, called "Sericulture", has not changed very much in the thousands of years since the silkworm's thread was first used in ancient China. Wooden trays may be exchanged for the more sanitary plastic ones. Powdered chow is available for those without access to fresh mulberry leaves, making it possible for more people to grow silkworms, and at times of the year when the mulberry leaves are not around. These few changes have had little bearing on the silkworm's care or cultivation. It is still a hands-on process involving live creatures, and takes a lot of time. But the result is certainly worth all the work and will certainly give anyone a truer understanding of why silk has been so desirable and so expensive throughout history.
Why You Don't Want to Grow Silkworms:
Before I wax too poetical on this subject, let me point out that sericulture is not for everyone. It takes a lot of time, for one. During gestation, which lasts approximately three weeks, the eggs must stay between 78 and 88 degrees F, in a tray with high humidity. As they hatch, each of the tiny creatures must be carefully moved to a petri dish containing their food. Every few days, they need to be moved to a clean tray with fresh food. For the last week or two of their lives as caterpillars, they'll need to be fed and moved every single day. If you have a large colony of silkworms going, feeding and moving all the silkworms can take most of an evening, and uses a lot of trays. And you have to make sure you always have plenty of food on hand, because even one missed feeding can kill. Continued food shortages can decrease the quality of silk any survivors make. Even once they cocoon, you're not through taking care of them, not if you want future generations. Ten to fourteen days later, they'll start to emerge from the cocoons, and the new moths must be moved to another tray so the mess they make while mating and laying eggs doesn't get all over your hard-earned silk.
Silkworms also produce quite a lot of... well, in cultured circles it's called frass, but it's really excrement. Every time the trays are emptied, each tray contains quite a lot of it. That's what most of the food they eat is turned into, and they eat a LOT of food! Now, there are uses for this frass. My roses absolutely love it, which is a good thing considering how much of it they get when I'm growing silkworms. But the frass also gets onto things, like the paper lining the trays, their food, and of course the early silk that they make all over the trays while they eat. Cleaning the trays is not a job for the weak-stomached.
Equipment:
If you're ready for the experience of growing your own silk from the egg, there are a few things you'll need:
The Silkworm Life-cycle:
Silkworms gestate in the egg for about three weeks, although those purchased from commercial growers have usually been brought to within about a week of hatching. During this time, their environment must be humid and between 78 and 88 degrees (F). My original supplier suggested using an incubator, but I've found that the air in my home is usually within their range. The eggs should be placed in a tray with a folded piece of paper towel that is kept damp through gestation.
When the baby silkworms emerge from their eggs, they are tiny, about the size of a lowercase "i", and almost black. Within 24 hours, they need to be carefully flicked into a petri dish containing fresh chow or small pieces of young mulberry leaves. If you don't want any escaping to die of hunger, make sure you replace the lid after every time, after checking to make sure none are out! Two days later, the silkworms will need to be fed again, but will still be too small to be casually moved around. Instead, gently add more food to their dish.
Two days later, the silkworms will need to be fed again, but this time they will need to be moved to dishes containing fresh food. Thankfully, by this time there should be a good layer of delicate early silk covering the dish, so you can move the silk matting instead of the individual silkworms (silk production and the need for fresh food are both at least partly dependent on the number of silkworms involved). If you have a large colony of silkworms, you might want to divide the colony at this time, putting them in two or more separate dishes. There may also be several silkworms remaining in the old dish. They should be fine for a while, but pick them out and put them in a clean one as soon as you can -- definitely before the chow dries out or molds.
By the next feeding, the silkworms should be big enough that they no longer need to be enclosed in the petri dish. Take the silk matting and lay it beside strips of fresh chow in a paper-lined lidded tray. Carefully move the other silkworms to the new trays as necessary. Continue feeding and moving the silkworms every two days, dividing the colonies when the silkworms are too large or hungry for the numbers in that tray. By the fourth week, the largest of the silkworms will be more than two inches long, fat, and hungry enough that they need to be fed every day.
Cocooning is a time-consuming process, and one for which you'll need a ready collection of cocooning supplies. Sometime during the fourth week, you'll notice some of the larger caterpillars climbing the walls of the tray (they've done this before, to shed their skins, but this time their heads will be pointing toward the lid) and moving their heads in a "figure-eight" motion. They're starting to lay out the support strands for their cocoons, although they may not yet be serious about cocooning. If you move them to the cocooning trays before they're ready, they'll starve, but an easy test confirms their readiness. Just pick them up and look between their rear pair of legs, from the underside. If you see a gray mass there, the caterpillar isn't quite ready, but if it's milky and translucent, the silkworm has pooped its last and is definitely ready to cocoon.
Place each silkworm in a cocooning support in a clean, paper-lined tray. I prefer shortened pieces of toilet paper or paper towel rolls for my cocooning supports, dipped once in melted wax to make it easier to remove the finished cocoon, but egg cartons are often suggested. Close the lid and leave the silkworms alone until the last one in the tray to cocoon has been finished for two or three days. You might want to use small pieces of masking tape on the lid to date each cocoon, so you know when it's safe to move them.
About three days after the silkworms in a tray make their cocoons, it becomes safe to take them out of their supports and consolidate the cocoons into a smaller number of trays. Remove the fluffy silken support structure, which can be cleaned and spun. Remove the unsatisfactory cocoons, the ones that aren't thick enough to be relatively hard. Their silk is useful enough, but you don't want bad genes in your pool. Lay the satisfactory cocoons in a clean tray lined with paper, with enough room between them so they only take up about half the floor space in the tray. Wait about a week for the new moths to emerge.
When the new moths do emerge, put them in an empty tray and let them do what you let them live to accomplish. The males (small) will die once the deed is done, while the females will stick around to lay about 200 - 300 eggs each. These eggs will be milky when first laid, but will darken over time to a dark gray. When the wax paper is reasonably covered with eggs, move any remaining moths to a new tray and cut the paper up into colonies of whatever size you'd prefer to grow next time. Place these colonies in a container and put it in your refrigerator until you're ready to grow some more silk.
Supposedly, the silkworms need at least a month's worth of "cool weather" before they are ready to finish incubation. Cocoons containing moths need to be stored in the freezer until they can be used, so the body doesn't decompose on the silk, but cocoons from which the moth has been allowed to escape can be stored at room temperature.
Possible Problems:
If water condenses on the lid of the tray or dish, prop up the lid and try to get a little more airflow into the container. Excessive moisture, aside from being dangerous in and of itself to the silkworms, can lead to mold growth if left unchecked.
If mold does grow, take the silkworms out of that tray immediately. Put them in a new tray, with all-new food, and keep an eye on your moisture levels!
If the food dries out too rapidly, try folding up a damp paper towel in the tray to raise the humidity. Also, check the temperature, which may be high.
If the silkworms look limp and sluggish, it may be too hot for them. Alternatively, if they look this way after being fed lettuce or another stopgap food, you may have fed them pesticides by not rinsing the food thoroughly.
If you seem to always be finding a few dead silkworms in each tray, don't be overly concerned. While a dramatic increase in the mortality rate is reason for concern, silkworms ARE insects, and you can expect that less than a quarter of them will reach full maturity. The mortality rate would be MUCH higher in the wild. Just toss them under one of your favourite non-food plants.
If it's cocooning time and some of your silkworms won't cocoon, continue feeding them and cleaning their trays as if they were doing exactly what they were expected to do. Some may have been late hatchers, others may be runts that now need some time to catch up. Still others never will cocoon. It's a simple fact of nature. At least if you continue caring for them, you're likely to get the maximum number of cocoons from them.
Processing the Cocoons:
To release the seracin and unwind the cocoons, place a few of them in a pot full of hot water. If you're going to reel the silk, find the ends of the strands, attach them to your reel, and wind off.
If you can't reel the silk, your primary aim is to loosen the cocoons enough that you can get the chrysalis or moth out so it doesn't soak up water and possibly stain the silk. Pull off hanks of silk and lay them on a folded towel, continuing until you can ease one end of the cocoon open and remove the remains. Once done, set the cocoon aside to be finished after this has been done to all the cocoons in the batch. You will need to change your water several times, as the chrysalis and other matter will stain the water. Eventually, you will have a mass of silk filaments that need to be fluffed and shortened so they can be easily spun, but which will then be far more enjoyable to spin than any other fibre.
Bibliography:
Crockett, Candace. Card Weaving. Loveland, CO: Interweave Press, 1973. Revised 1991.
Crowfoot, Pritchard, and Staniland. Textiles and Clothing c. 1150 - c. 1450. From the Museum of London's "Medieval Finds From Excavations in London" series. Norwich, UK: HMSO, 1992.
Franck, Irene, and Brownstone, David. The Silk Road: a History. NY: Facts on File Publications, Inc., 1986.
Gies, Frances and Joseph. Women in the Middle Ages. NY: Thomas Y. Crowell Co., 1978.
Joseph, Marjory L. Introductory Textile Science. NY: Holt, Rinehart, and Winston, Inc., 1966.
Kolander, Cheryl. A Silk Worker's Notebook. Loveland, CO: Interweave Press, 1979. Revised 1985.
Mulberry Farms. "Hatching and Raising Instructions". This is part of a pamphlet sent along with each order of silkworm chow or eggs.
Sericulum: the Science of Silkworms for the Course of Nature. <http://sericulum.com/>. This was the first place I found information on cultivating silkworms, and contains excellent instructions for growing them by modern methods.
Whitfield, Susan. Life Along the Silk Road. Berkeley, CA: University of California Press, 1999.
Silkworm Sources:
Mulberry Farms: <http://www.mulberryfarms.com>. This company sells silkworms, eggs, food, and equipment for the average consumer, who they expect is probably growing the silkworms as lizard food. However, I have not had a problem with their products, and they are genuinely friendly and curious about silkworm cultivation for silk production.
Sericulum: <http://sericulum.com/>. This was the first place I found information on cultivating silkworms, and contains excellent instructions for growing them by modern methods. They tend to focus on silkworm cultivation for laboratory or classroom use, but their information is certainly valid. Their prices are significantly higher than those of Mulberry Farms.
Please feel free to share this handout for educational purposes, as long as my name remains attached.
Email me if you have any questions about sericulture or this handout.