The Secrets of Raising Silkworms

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The product of a successful season raising silkworms. That paper grocery bag holds about 10,000 cocoons, each composed of 600 to 1,000 yards of thread—enough to produce about 5 pounds of raw silk or about 30 pairs of silk stockings.
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Marry Stock demonstrates a method of rolling waste silk into a strand.
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The tiny black spots on the tissue are eggs, which will hatch into silkworms (shown munching on a mulberry leaf) in about three to ten days. After 30 days of grazing, these critters will encase themselves in robes of silk, producing cocoons a little larger than a quarter. Silkworm farmers may kill the fat, brown pupa (on the paper towel) that inhabits the cocoon, or allow the chrysalid to hatch into the silkworm moth (again, perched on the leaf). Such adults will soon mate, reproduce, and die ... thereby completing their life cycle (the entirety of which is shown in this photo!).
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Marry Cook skillfully spins a cocoon into thread.

If you’re tired of the same old arts-and-crafts scene and
looking for an exciting, different part-time pursuit,
give some thought to the inexpensive, mysterious, Oriental
practice of raising silkworms (aka sericulture or silkworm cultivation).

The knowledge needed to raise such tiny “livestock” has
been handed down from generation to generation for
centuries. Today the silkworm ranks with the honeybee as one
of the world’s most profitable domestic insects.

Mary Stock (who lives in Canton, Ohio) started a silkworm
farm more than four years ago, and she’s been kind enough
to share her knowledge with MOTHER EARTH NEWS’ readers. In ancient
China, revealing such silkworm secrets would probably have
resulted in death by torture, and–even
today–printed matter on the subject is hard to come
by–most available texts are written either in highly
technical terms or in Oriental languages!

The Egg and You

Ms. Stock says that–in sericulture at
least–there’s definitely no question about whether
the moth or egg comes first. It’s the egg every time,
and these “silkworm seeds” are very difficult to find. In
fact, so few folks raise the little silkmaking machines
nowadays that Mary had to do a good bit of searching before
she located a supplier–Marguerite Shimmin of Pasadena, CA–and bought 200 eggs from that lady for $2.00. It was all the money Stock had to invest
to get her start in the silkworm business.

There is, however, one other requirement for successful
sericulture: a ready supply of mulberry leaves. The most
important variety–as far as hungry silkworms are
concerned–is Morus alba, the white-fruited mulberry
of China. This is a hardy tree that will grow in almost any
soil, and worms fed on its leaves are said to produce the
finest silk. Another popular species is the Morus nigra, or
black-fruited mulberry, which is native to Italy and
produces berries that make a great syrup or pie. You’ll
find, however, that the caterpillars will munch away on any
kind of mulberry leaves you happen to have on hand.

Three-year-old trees produce the best feed for silk
production, and a healthy mulberry should yield from 20 to
30 pounds of leaves during the time your worms are in their
growing stages. (That’s about enough greenery to supply 100
wrigglers with chow for the 30 days–more or
less–that they’ll need food.)

You may be able to locate silkworm eggs through your local
spinning and weaving organizations. It these sources don’t
pail out, though, you can write to Marguerite in Pasadena
or Mary.
Both women will be glad to share their knowledge and egg
supplies, but be sure to send a self-addressed, stamped
envelope–and at least $2.00–with any request
for eggs or information.

Then, should your packet of “silkworm seeds” show up before
the local mulberry trees are in leaf, keep the embryos at
about 50°F (just place the paper towel or
napkin–on which the eggs arrive–in a sealed
jar, and store the container in the crisper compartment of
your ‘fridge) until it’s time to hatch them.

Worm Incubation

Once your trees have produced a good supply of feed, it’s
time to “plant” your silk crop. Simply place the eggs–still
on their paper–in any available container (such as a
shoebox or dishpan) and put ’em in a warm, dry, well
ventilated spot. It’s very important to keep all the eggs,
worms, cocoons, and moths out of drafts and direct sunlight. They do need plenty of fresh air, so it’s best not
to smoke around silkworms at any stage of their
development. The temperature of the incubating box should
be increased gradually over a couple of days, and then
‘maintained as nearly constant as possible. Anywhere
from 68 to 77°F will do.

After three to ten days in the box (depending on warmth,
humidity, and other factors) the majority of your eggs will
hatch within one ten-minute period, usually during the
early morning. This means that you can wake up to find that
you have 200 very hungry mouths to feed! Any worms that
don’t hatch out with the first group probably won’t put in
their appearance until the following day. These late eggs
should be placed in another box, since they’ll be on a
different molting and spinning schedule from the first-born

Keep in mind that your infant silkworms will be less than
1/8 of an inch long. Yet, one short month later the
critters will have attained 10,000 times their initial
weight. All that growth has to be fueled with
mulberry leaves.

Care and Feeding

For your worms’ early feedings, remove the leaf stems and
use only the tenderest top-of-the-tree leaves (remember to
strip the branches from the base to the tip in order
not to tear the bark or injure new buds). Such “starter
feed” should be chopped into 1/4-inch squares and–if
there’s even a chance that the bush has been sprayed–washed
and thoroughly dried before the fodder is sprinkled evenly
about the box. It’s best to pick the leaves fresh each day,
but an emergency supply can be stored in the crisper of
your refrigerator if, again, the greens are dried out
before they’re offered to the hungry little critters.

The more your new charges eat, the bigger they’ll get and
the more food they’ll require. If you underfeed the worms
at any point, they may become so ravenous that they’ll
overeat at the next meal and make themselves sick. Constant underfeeding can even lower the quality of their
silk! The trick is to give your worms adequate, regular
feedings, never let them run out of food, and always remove
old, wilted leaf pieces from the box.

In addition, the silkworms will be healthier if you clean
their “litter” by regularly sliding in fresh, dry pieces of
paper and removing (to the compost pile) the soiled
sheets. When this isn’t done, molds can
form that could give rise to a number of worm diseases.

Though the caterpillars seem to eat more in the mornings
and evenings, they’re actually chowing down at all hours.
The only times the worms will stop chewing are during their
four molting periods, which occur about every five or
six days.

Shortly before each molt, the heads of the worms will
swell, their skins will lose color, and their bodies will
become transparent and immobile. (It’s extremely important
that the larvae aren’t moved or disturbed in any way at
this time.) During the 24-hour “skin-shedding process” your
wigglers will go into a sleep and lose all interest in
food. Otherwise, their appetites are regular and enormous.

Mary Stock reports that silkworms get especially voracious
in the last week before they start to spin. While in this
stage her 10,000 charges consume two and a half bushels of
mulberry leaves a day. Though Mary already has 15 trees
on her 25-acre farm, she’s in the process of planting 25
additional seedlings! (Besides providing worm food, the
trees make great windbreaks and produce quantities of
useful berries.)

Pupa Preparations

As the caterpillars increase in size, divide the brood into
several containers. Each individual needs space to grow. You’ll want to avoid conditions that force the critters
to crawl over each other, because their velvet skins are so
delicate that even silkworm feet can tear them. When you
transfer the fragile larvae, it’s best to wait until they
climb onto their food and then remove each worm–leaf and
all–to new quarters.

Once the “spinning time” approaches (after three weeks or
so) provide containers with lots of edges, so your wiggly
weavers can quickly set up the “guide wires” from which
they’ll hang their silken shelters. A number of small
strawberry boxes or egg cartons will be fine for this
purpose.

Then suddenly–anywhere from 25 to 32 days after
hatching–your caterpillars will stop eating and start
to produce silk.

You’ll be able to tell when a worm is ready to spin,
because it will appear sluggish. Often the critter’s head
will move from side to side as it seeks a suitable location
for its new home. (Since the larvae have no eyes, try to
make sure that they don’t have to travel far to find a
suitable corner.)

A silkworm “sets up shop” by secreting a filament from an
orifice located just below its mouth. As strands leave this
opening, they make contact with another secretion called
sericin which becomes sticky when it’s exposed to the air.
This “glue” allows the incredible little workers to set
their guide wires and shape their cocoons.

After the caterpillar has anchored its crude hammock, it
will lie on its back, double up its legs, contract its
body, and force the filament from within. The small spinner
won’t take the easy way out and weave Its womb in circles
from one end to the other. Instead–with its head bobbing
and weaving at a rate of 69 times per minute–the amazing
creature produces a pattern of figure eights, layer upon
layer, until its shell is formed.

You’ll soon lose sight of the hearty worker but will still
be able to hear it spinning until its complete supply of
body fluids so magically created from mulberry leaves is
consumed. If you could see inside the finished case, you’d
find that the once-plump, three-inch-long caterpillar has
been transformed into a shriveled-up pupa of about 1 1/4
inches in length. The entire spinning process takes about
three days, and it’s a show that beats the stuffing out of
anything on television!

The Harvest, and After

While the tired pupa turns itself into a moth–a
process that takes from ten days to two weeks–you’ll
have a decision to make: If you plan to raise silkworms
again the following year, it’ll be necessary to select some
cocoons that will be allowed to complete their life cycles.

Naturally, it’s necessary to choose a fairly equal number
of males and females to carry on your line, and the best
way to sex these critters is to take a close look at their
protective envelopes. A male produces a structure that
resembles a peanut slightly hour-glass in shape and
somewhat pointed at the ends–while the “ladies” are
most often found in larger, oval-shaped sheaths. Keep in
mind that one moth lays from 300 to 400 eggs, and that 80
or 85% of those will hatch. Two dozen cocoons will,
therefore (assuming that half of them contain females),
yield enough “seed” to hatch about 3,000 crawlers.

The nests that you select as your “laying stock” should be
removed from their boxes and set aside in separate, clean,
dry containers. There’s no trick to plucking the little
silk houses from their moorings … just tug ’em gently and
they’ll release. (Some waste silk will cling to the box and
cocoon, though. Pull this material loose and save it, as it
can be woven into a beautiful rough cloth called shantung.)

Traditionally, the rest of the cocoons–which vary in color
from light brown to creamy white, with a little lemon
and pale green thrown in–are harvested anywhere from
seven to ten days after the caterpillar begins to spin.
It’s necessary to kill the pupas inside those nests that
are to be used for silkmaking. (If you don’t, the
chrysalids will soon emerge as moths, and–during this
process–the insects produce a solvent which destroys
the continuous filament of the silk fiber.) The easiest way
to accomplish this unpleasant but necessary task is to put
the cocoons in a paper bag and place the sack in a 200°
F oven for 20 minutes. Long exposure–at least six
hours–to bright sun will also do the job.

After the pupas are killed, you can relax for a few days
before you reel and spin your silk. But don’t rest too
long, or the material will take on a distinctive aroma from
the dead chrysalids inside.

And what kind of harvest can you expect ? Well, perhaps not
much the first year (it takes about 2,000 cocoons to
produce a pound of raw silk, and some 350 to make a pair of
stockings! ) but enough of a crop to see whether you really
enjoy the art of sericulture.

Make Your Own Tools!

One of the great things about harvesting silk is that most
of it can be reeled directly from the cocoons with a simple
homemade tool. Just find yourself two dark-colored pieces
of paperboard–each about 10 inches square–and a
short stick or clothespin. Cut a slot halfway to the center
of each board, and interlock the two sections so they
resemble the paddle wheel of a boat. Then, to make a
“twirling” handle, clip a clothespin just above or below
the intersection of the squares (or cut a slot in a dowel
or stick and slip that handle in place).

Next, bring a small pan of water almost to a boil. (If you
use a container with a dark interior, you’ll find it easier
to locate the filaments of silk.) When the liquid is ready,
drop five to eight cocoons–depending upon how heavy
you want your thread to be–into the, pan. Most
commercial silk is eight strands thick, but five fibers will
also work well; the incredible strength of each
strand is equal to (or greater than) that of a filament of
steel of the same diameter!

After a few minutes the water will begin to dissolve the
glue, and you’ll see the tiny strings float away from the
cocoons. Use tongs to catch the filaments, twist them together in the fingers of one hand while your
other hand slowly reels the thread onto the paperboard
spool. When you get to the end and the pupas drop into the
water, tie a small knot to keep the thread from unraveling.
(Remember, you’ll be winding 600 to 1,000 yards of silk, so
start the job in the morning. Don’t wait till an hour or
so before bedtime! )

The reward for your (and the silkworms’) labor is a thin,
continuous thread of the finest material available. Silk
weighs less than any natural fiber, yet a strand thinner
than a human hair can be stretched five to six inches a
yard and still return to its original length!

When we visited Mary Stock, she showed us the ancient art
of “skin spinning” the waste silk. Here’s how to do it:
Take a short, straight piece of coat hanger and make a
slight hook (about 1/4 inch across) at one end. Then, use
this tool to pull at the bundle of raw silk you’ve
accumulated. As you separate a thin string of fibers from
the mass, roll it on your leg to form a strand. You can also use a
drop spindle, or even comb the waste silk with a
cotton-carding tool and spin it on a wheel. Remember that
silk is an extremely fine fiber, though, and must be
handled with care.

The silkworm’s sticky sericin–some of which will
remain on the filaments–makes the thread a bit stiff
and lackluster. However, it’s best to weave the silk before
you give it a final wash in mild soap and water to remove
this gluey substance.

A New Generation

Meanwhile, back at the breeding box, you can watch the
Bombyx mori–the mulberry or silkworm moth–put
in its brief appearance. The “great awakening”–as
the Chinese called this event–takes place as the moth
secretes its alkaline saliva, which softens the end of
the cocoon and allows the adult insect to step into the
world.

The wings of the male moth have a distinct sickle shape,
and will soon dry and grow as the insect flaps them. The
females can be easily identified by their larger abdomens.
Neither sex is able to fly, and the “ladies” rarely stray more
than a few inches from their cocoons.

Since the moths are not equipped to eat and sustain
themselves, mating and egg-laying take place soon after
they emerge from their cocoons. Be prepared–by
placing some paper towels in the nest boxes–to remove
the sticky eggs with as little disturbance as possible.
Should a moth lay its tiny treasures on a cocoon, just snip
them off and place ’em with the other eggs dropped (you
hope) on the paper. Then, let the new seed dry for a few
days before you store it.

Following mating and reproduction, both sexes of moth will
die within a few days, bringing the silkworm story
full circle. Take the poppy-seed-like eggs and place them
in a small (labeled) jar to be saved in the crisper
compartment of your refrigerator for next year’s effort.

As a potential “worm rancher,” you’d probably like to know
what kind of profit you can expect from your work. Well, in
terms of money from the sale of thread, the rewards
probably won’t amount to much unless you have groves of
mulberry trees and a number of hands to help you out in
spring and early summer. But, on the other hand, so little
silk is produced in North America that the market is wide
open, and there are other ways to turn your hobby into an
income besides selling material!

Both Mary Stock and Marguerite Shimmin, for example, find
themselves in great demand for sericulture lectures to
schoolchildren, clubs, and craft groups. Marguerite is
sometimes commissioned by museums to make repairs in old
tapestries, and Mary tells us that her homegrown silk is
snatched up by area weavers for around $35 a pound! So,
despite the time and effort required to grow and harvest
their silk crops, both of these women feel well rewarded
for their labors.

In addition to any monetary gains, though, sericulture
offers a rare opportunity to understand the workings of
nature, and a chance to appreciate the time dedication
involved in the miraculous transformation from “mulberry
leaves [to] satin.” For many folks, those will be reasons
enough to give silkworm cultivation a try.

All Around the Mulberry Bush….

If you’re interested in pursuing the art of sericulture,
but lack a source of mulberry leaves to feed your
“livestock”, you can prepare to start your own silk farm
next year by ordering some seedlings of the necessary tree
now! The Gurney Seed and Nursery Company sells three-
to four-foot-high, two-year-old trees for $5.55 apiece or
$24.95 for five … while J.E. Miller Nurseries, Inc.
offers four- to
five-foot, two-year-old trees for $5.45 apiece, or two for
$9.95.