This document is a resource for K-12 educators. It contains curriculum ideas, silkworm-raising instructions, and the history of silk. Imbedded hyperlinks allow the user to skip around in the document. The most current version is available on the Internet at http://www.mediamessage.com/kayton .
Introduction
History of silk
Silk thread and cloth
Science questions and FAQs
Internet links
Teacher resources
Classroom activities
Display case
Silkworm poem
Raising silkworms
Schedule
Eggs
Container
Mulberry leaves
Newborn caterpillars
Older caterpillars
Spinning a cocoon
Pupa and moth
Trouble-shooting
Silkworms are easy, fun and educational to grow in a classroom or at home. Most children think they are cute, and nobody is allergic to silkworms. They are easy to care for and can help make your students excited about science.
After hatching from an egg, the silkworms eat mulberry leaves and grow larger. When they are finger-sized, they each spin a cocoon, pupate inside the cocoon, then emerge as a moth to mate and lay eggs. The eggs hatch into silkworms in a few weeks, and then the cycle continues.
Silkworms go through four stages of development, as do most other insects: egg, larva, pupa and adult. The larva is the silkworm caterpillar. The adult stage is the silkworm moth.
Silkworms were originally domesticated in China thousands of years ago. Stories have been handed down through the generations and are based party on fact and partly on legend and myth.

The tale which persists is that about 2,640 B.C. a Chinese empress, Si-Ling-Chi, was watching the glistening amber cocoons that little worms were spinning in the mulberry trees in the palace gardens. She unwound one of the threads on a cocoon and found that it was one, very long strand of shiny material. Fascinated, she pulled strands from several cocoons through her ring to form a thicker thread. Eventually, with the help of her ladies of the court, she spun the threads into a beautiful piece of cloth to make a robe for the emperor, Huang-Ti. This magnificent material, silk, became known at the "cloth of kings".
For thousand of years the royal family of China had silk. The Chinese kept the secret of how silk was made for 2500 years. Silk cloth was sold to the West, but the source of the shiny thread that made the material was not revealed. The penalty in China for telling that the silk came from the cocoons of the little silkworms was death! Some very strange ideas were formulated by Westerners to explain the origin of silk. Here are a few: Silk came from the colored petals of flowers in the Chinese desert, silk was made of wondrously soft soil, silk came from a spider-like animal that ate until it burst open and the silk threads were found inside its body, and silk came from the silky fuzz on special leaves. These ideas seem far-fetched today -- but in ancient times they were serious theories.
Legend has it that the Japanese carries off four Chinese maidens, who knew the secret of silk, along with mulberry shoots and silk moth eggs. Today Japan is the leading producer of silk! Another story is that a Chinese princess married an Indian prince. She carried silkworm eggs and mulberry shoots to India in her elaborate headdress and the secret of raising silkworms in her head.
Two Christian monks told Emperor Justinian of Constantinople that they had learned the secret of silk. Justinian send them back to China to get eggs and mulberry shoots for him.
They returned many years later with the eggs and shoots hidden inside their hollowed-out walking sticks. Since Justinian was the emperor of Constantinople, a crossroads city, the secret soon spread throughout Europe. There are many more interesting stories about the history of silk. Have older children do some research in the library and report to the class.
Today silk can be worn by anyone -- not just emperors and noblemen and their families.
Silk is made into many lovely fabrics, such as satin, velvet, chiffon, crepe, brocade, taffeta, faille, and shantung. A good class project would be to see how many different kinds of silk cloth could be collected and put them on a chart for the kids to see and feel. The beautiful colors of silk would also make an excellent chart.
Modern silkworm moths have been bred to make white silk instead of the amber-colored silk of their wild ancestors. They also have large, fat bodies and tiny wings, so they cannot fly. This makes it easier for silkworm farmers to raise them (and easier for teachers, too!). If you were to release a domesticated silkworm moth into the wild, it would not be able to survive or reproduce.
If the silk moths are allowed to emerge from the cocoons, they would make holes in the silk thread. Silkworm farmers kill the pupas inside the cocoons by baking

them in a hot oven. Then they soak the cocoons in boiling water to loosen the threads. A person finds the end of the thread and places it on a winding bobbin. Then a machine unrolls the cocoon, winding the silk from five cocoons together to make one silk thread.
Then the thread is woven into cloth. Zhejiang province of China is the main source of
Chinese silk, and contains more than three hundred silk mills.
The Latin (scientific) name for the silkworm is bombyx mori. Silkworms are insects. All insects have six legs in the adult stage. Silkworm caterpillars have six real legs, plus five pairs of pseudopods (false legs) on the rear of the body. The very rear of the body, which is split, is used for grasping twigs and leaves. Insects have no backbone or skeleton, but instead have an exoskeleton (exterior shell). Some insects like cockroaches have a hard, crunchy shell. Silkworms and silkworm moths have a soft skin. Silkworms shed their skins four times while growing. These growing stages are called instars.
Are silkworms warm-blooded or cold-blooded?
Silkworms are cold-blooded, as are all insects. A warm-blooded animal always has the interior of its body at the same temperature (98.6°F or 37°C for a human) unless it is sick. If their interior temperature gets too high or too low, it will die. A cold-blooded animal's interior temperature is usually within a few degrees of the air around it.
The only warm-blooded animals are mammals and birds. All animals without backbones are cold-blooded, which includes silkworms and all other insects. However, while moving around, all animals' muscles generate heat. If you have a covered container with lots of big silkworms, when you take the lid off, you can feel the heat that was trapped in the container.
How can you tell if a silkworm is male or female?
Male moths are smaller, and have a flap of skin at the rear. Females periodically extrude a yellow T-shaped scent gland out their rear end. Look at the pictures in Sylvia Johnson's
book for close-up photos to help you distinguish male from female. The smallest
caterpillars, which make the smallest cocoons, turn into male moths. The big caterpillars turn into female moths. The medium-sized worms ones can go either way.
Why are some cocoons yellow while others are white?
Wild silkworms all make yellow silk, to be camouflaged with dead yellow leaves. Over the centuries, silkworm farmers selectively bred for whiter and whiter silk until they achieved the pure white we see today. Silk farmers prefer pure white because it can be dyed any color without having to bleach it first.
Some people have blue eyes and others have brown eyes. When a blue-eyed woman marries a brown-eyed man, some of their children will have brown eyes and others will be blue-eyed. Silk color works in a similar manner. Almost all commercial silkworms make white silk. There are a few silkworm varieties that make yellow, orange and pale-green silk. When you cross-breed a "white-silk" silkworm moth with a "yellow-silk" silkworm moth, some offspring will make yellow silk and some will make white silk. The color of silk is determined by the silkworm’s genes.

What do silkworm moths eat?
They don't eat (or drink) anything. They mate, the female lays eggs, and then they die within 3-6 days. Many other types of insects (like mayflies) follow this pattern. All adult butterflies and moths have mouth parts and digestive tracts adapted for sipping liquids.
Silkworm moths still have a mouth and rudimentary gut, since they're descended from an ancestor that fed in adulthood.
Do silkworms have brains?
Silkworms operate entirely on instinct. They have a group of nerve cells that controls their bodies, but it is too rudimentary to be called a brain.
A teacher in Pennsylvania, USA has information at http://www.thewildones.org/Curric/silkworm.html
An excellent five-minute slide show about silk and silkworms is available (from Cincinnati,
Ohio, USA) at http://BugLady.clc.uc.edu/showit/silk.htm
. Note that the file takes about 15 minutes to download on a 56K modem, so be patient. It's worth it! You will need a special viewer to see the slideshow. The website has a place to click to download the viewer. When you download the viewer setup program, save it in C:\Downloads. Then open up C:\Downloads to install it. The computer will ask where you want to install it. For
Netscape, install into C:\ProgramFiles\Netscape\Communicator\Programs. For IE under
Win95, install into C:\ProgramFiles\Plus!\Internet Explorer, For IE under Win98, install into
C:\ProgramFiles\Internet Explorer. For help with installation, email the author.
General information on butterflies can be found at http://cse.unl.edu/~scotth/samantha/moths-butterflies.html
or http://snapper.bio.umass.edu/kunkel/Moths/strecker_silk.html
If you would like to download gorgeous silkworm pictures in incredible detail (but it will take a VERY long time - each file is around half a megabyte), check out http://www.silkchina.com/silkchina/worms.html
A site with general butterfly information (but it loads VERY slowly) is http://butterflywebsite.com/awards/showawards.cfm
Silkworm information in Spanish can be found at http://insected.arizona.edu/espanol/sedainfo.htm
Please email the author if you find other worthwhile sites!
There are many ways to integrate silkworms into your curriculum. Some teacher-tested ideas appear below. If you have ideas to share or have questions about silkworms, please email the author kayton@alum.mit.edu.
The book Silkworms, by Sylvia Johnson, is excellent for children and adults alike. It has amazing photos. Most bookstores can order it, or you can order it from

http://www.amazon.com
. The paperback is ISBN 0-3225-9557-5 (about US$6). The library binding edition is ISBN 0-8225-1478-8 (about US$16).
Try these teacher-tested ideas or invent your own!
Silkworm math . Have the children measure the length of the silkworms and graph them as they grow.
Rainfall : When the silkworms are large, take the lid off the container and have the children be extremely quiet. They will be able to hear the sound of the silkworms moving around! It sounds like a gentle rainfall. The sound is not chewing, but their little suction-cup feet lifting off the leaves and plopping back down again.
Silkworm pet . Give each child a silkworm in a small cardboard cup or carton. Have them put in a fresh leaf twice a day, and empty the droppings and dried leaves. Put in a stick and they can see the silkworm crawl around. Wait until the caterpillars are two weeks old since there is a high mortality rate for the first few weeks.
Heartbeat . With a full-grown caterpillar, you can easily see the heart pumping blood through the translucent skin. The heart is located at the rear end of the caterpillar on the top. You can see it pulse. The main artery carrying the blood is where the backbone would be if it had one.
Egg laying . If a female moth is laying eggs, have the children watch. You can actually see the yellow eggs emerge one at a time from her rear end! She feels around with her ovipositor ("egg-layer" in Latin) until she feels an empty place to put the egg.
Coarse thread . You can make silk thread without killing any of the pupas. When the cocoons are spun, there is a fair amount of loose silk on them. Have the children gently pull it off the cocoon, making sure not to crush it. They can then roll it between their fingers to make a coarse silk thread.
Fine thread . In order to unwind the cocoon, you must kill the pupa inside. Place the cocoons in a 200°F (90°C) oven for 30 minutes. Then drop the cocoons in boiling water.
After five minutes, you can reach in (wearing rubber dishwashing gloves), and begin to unwind the cocoon. Unwinding five at a time will make a fine, strong, thread.
You can make a display case showing the children each stage in the silkworm cycle. Buy a clear plastic box frame 11"x14" (28 x 35 cm). A box frame is about 1-1/4" (3cm) deep so you can put three-dimensional things in comes filled with a cardboard box. it. It
Cut out the one of the 11"x14" (28 x 35cm) sides of cardboard box, making a hollow frame.
Put captions on an 11"x14" (28 x 35 piece of paper and glue it onto the cm) inside

of the cardboard frame. Now glue dead moths, cocoons, silk thread and silk cloth in the appropriate places. Cut out leaves from green construction paper and glue them in, too.
Make newborn "silkworms" from pieces of thick black thread. Make older "silkworms" of various sizes from white or gray clay. Let the clay “worms” dry before gluing them down.
Eggs can be yellow clay, Play-dough, beads, sesame seeds, or dots of yellow dimensional fabric paint. Tape the cardboard frame inside the plastic box and admire your work!
Use clear silicone glue for best results (it comes in small tubes like toothpaste).
I saw a tiny silkworm.
It had a funny name.
My teacher called it larva,
But it wiggled all the same.
One day it changed from hairy to smooth --
From black to very white.
Its body was much bigger, too,
And it did it overnight.
It changed like this
Just three more times
And always in between
It ate and ate and ATE and ATE
Mulberry leaves so green.
One day it stopped,
And started to spin
A shiny silken thread.
Around and round in figure eights
It moved its little head.
It made a cocoon so snowy white,
Its neighbors made theirs yellow and bright.
And then inside where none could see,
A pupa formed, my teacher told me.
One day it pushed from its cocoon --
How different it looked now.
It fluttered about on weak, little wings --
A silkworm moth --but how??
It laid so many golden eggs
Near its empty white cocoon.
I wondered when the larva would hatch.
Would it be very soon?
Egg to larva to pupa to adult --
Is a strange, strange way

To change from being born
Into a grown-up moth, I'd say!
You will need a small amount of space on a table, access to fresh mulberry leaves, silkworm eggs, and the information below.
Each stage of the silkworm cycle takes time, as shown below:
Eggs hatch in about 7-20 days after removal from refrigerator.
Caterpillars eat for about 26 days before spinning silk.
It takes about 3 days to fully spin a cocoon and turn into a pupa.
The moth emerges from the cocoon after about 21 days.
The female moth lays eggs about 2 days after emerging from the cocoon.
TOTAL from start to finish – about 60-72 days
Get eggs from a friend or order from either Niles Biological, http://www.nilesbio.com
,
U.S.A. telephone (916) 386-2665 or from Carolina Biological, http://www.carosci.com
,
U.S.A. telephone (800) 334-5551. The cost is about US $10 for approximately 30 eggs.
The author will mail free silkworm eggs in exchange for foreign and unusual automobile license plates (number plates) since her children collect them. Contact her by email at kayton@alum.mit.edu.
Once your eggs arrive, put the eggs in the refrigerator (NOT THE FREEZER!) so they won’t hatch until you are ready to use them. Once eggs are removed from the refrigerator, they will usually hatch in 7-20 days. Warm weather and direct morning sunlight hastens hatching.
Silkworms get their moisture from leaves so they must be fresh, not dried-out. Unless you want to change leaves three times daily, you will need a covered container in which to raise the worms. It should be almost airtight to prevent leaves from drying out, but must have small air holes for ventilation. Use a transparent plastic cake cover with the handle removed to allow air in through the screw-holes(or drill your own holes). In California
U.S.A., cheap cake lids are available from Smart and Final Iris restaurant supply stores.
You'll also need a tray or plate to put under the silkworms.
Silkworms only eat fresh mulberry leaves which are available in most temperate climates in the spring and summer. Silkworms will not eat any other food. In California, U.S.A., trees generally have leaves from mid-April through September. In the southern hemisphere, leaves are usually available from mid-September through March. You must plan to raise your silkworms when there will be leaves for them to eat. In the spring, mulberry trees

first produce pollen bodies but no leaves. About two weeks after the pollen bodies appear, the first leaves begin to form on the trees. It generally takes three weeks from the appearance of the pollen bodies until there are enough leaves to feed the silkworms.
You will need to locate local mulberry trees (Latin name Morus alba). Make sure to get permission from the owners and verify that they don't spray their tree with insecticide. If possible, just pick leaves (don't break off branches), so leaves will grow back faster.
Leaves will keep fresh in airtight bags in the refrigerator for about 5 days. Please don't strip all the leaves off a tree. If an owner will allow you to break off a small branch, put it in a vase of water and pick leaves as necessary. A branch will last a week this way. Don't put caterpillars on a branch in water, since they will crawl into the water and drown. Don’t put your caterpillars on a mulberry tree since hungry birds will find them and eat them all.
Silkworms cannot remain unfed in a classroom over the weekend since they need fresh leaves. Usually the teacher or a student will take them home for the weekend. Make sure leaves do not have dew or water on the surface when feeding newborn silkworms, since they will drown in any small surface film of water.
Once you have located leaves and have a container ready, take your eggs out of the refrigerator. They will hatch in 7-20 days, depending on how far developed they were when they were put into the refrigerator. Placing the eggs in direct morning sunlight makes them hatch more
The silkworms usually hatch at dawn. Have a leaves ready (in a tightly-sealed bag) since they within a day of hatching. rapidly. few must eat
Newborn silkworms will barely nibble at the leaf. out before they eat the entire leaf. Change
It will dry leaves at least three times a day at this stage, so they quickly. If you have access to a low-power microscope (about 30x), let the children look at a will grow tiny caterpillar. Instead of a tiny black string, they will see that the body of the newborn larva is black with stiff little hairs. If you have no microscope,
look at the pictures in Sylvia Johnson's book .
The Japanese call this stage "kego", which means "hairy baby". If you examine the eggshell under a microscope, you can see the pores that let air inside while the caterpillar is developing. The edges of the hole where the caterpillar emerged are black.
Twice a day (three times a day if you have no lid), give the worms fresh leaves. Newborn silkworms look like small black strings this size __ . They are initially too weak to crawl from the old leaf to the new one. Either place the new leaf directly on top of the old leaf, or carefully by hand move all of the silkworms onto the new leaf. Throw out the old, dried leaf.
Put the new leaf with silkworms into the container and replace the lid. If any newborn

worms are on the paper with the eggs, gently move them onto a leaf (or place a leaf directly on top of the paper).
After five days, the worms will have the strength to crawl from the old leaves to new ones by themselves, so you won't have to move them by hand. Then you can just place new leaves in the container. Every two days, empty and clean the container to prevent mold from forming. You'll need to increase the number of leaves as they get older. Caterpillar droppings (frass) look like small black specks when they are little, and like miniature black corn cobs when the caterpillars are larger.
Silkworms will need to go home with the teacher or a child over the weekend since they need fresh leaves, and leaves dry out very quickly. The silkworms will shed their skin three times while growing. The shed skins are beige and usually roll up into a round wad. Sometimes the tiny silkworms will eat their shed skin. The larger ones don't. Each stage the silkworm goes through is called an
"instar". First instar caterpillars are black. The second and third instars are grayish-white with black heads. The fifth and final instar has a white head. In between each instar is a time of resting and molting. The Japanese say the silkworm is "sleeping".
The silkworm does 80% of its eating during the fifth instar. The silk glands now make up
25% of its body weight. The larva has increased its size 10,000 times since birth. If this happened to a six-pound human baby, it would weigh 60,000 pounds when it was grown!
The final instar of the larval stage is 2-3/4 inches long.
In each instar, the caterpillar has six real legs (as do all insects). It also has five pairs of false legs on the rear of its body. The body is made up of thirteen segments, each of which has a black dot on the side. These dots are called spiracles, and the silkworm breathes through them.
The silkworm eats continuously for twenty-six days. Then it stops eating and its cocoon. The silk thread from a single cocoon is about one-and-a-half kilometers mile) long. The caterpillars like to spin cocoons in toilet paper tubes (slice them to make two shorter cylinders), paper tubes (cut into six slices), or in egg carton bottoms. Silkworms are ready to spin spins
(one in half towel when they stop eating and turn yellowish. When they get finger-sized, put sliced toilet paper tubes or egg cartons in their container. You can make a "cocoon condo" by stacking toilet paper tubes in a pyramid.
The cocoon-spinning process takes about three days.
When they are spinning, try not to disturb their threads or

they will have to start over again. Once the cocoons are all spun, remove dried-up leaves to prevent mold from forming. The silk is actually hardened silkworm saliva. When the silkworm ate leaves, they were digested and nutrients were sent into the bloodstream. The silk glands absorbed these nutrients. The larva has a small spinneret on its lip, through which the silk emerges. The single strand of silk that forms the cocoon is about one mile long!
The silkworm moves its head in figure 8 patterns as it spins the cocoon. When the cocoon is partially made, you can see the head moving around inside if you hold it up to the light.
Inside the cocoon, the silkworm sheds its skin one last time and a brown-shelled pupa. Inside this shell, the pupa takes three change into the adult silk moth. When the transformation is the moth emerges from the cocoon. The adult moth has a special becomes weeks to complete, secretion cocoon. which is used to dissolve the silk so it can push its way out of the
When the silkmoths emerge, their wings are crumpled, but they pumped full of fluid and harden it about an hour. The moths get cannot fly since their bodies are large and their wings are small. The moths do not eat or drink.
Females silk moths are significantly larger than males. Females periodically extrude a scent gland through the hole in their abdomen. Males have a flap of skin at the end of their abdomen and flutter their wings frequently. Each moth will expel a reddish-brown fluid shortly after emerging from the cocoon. This fluid is like the moth's "urine" that it retained since it couldn't "urinate" while it was in the cocoon.
The silkworm moth mates with another moth within hours of emerging from the cocoon.
The moths remain mated for one day, then separate. The female lays eggs immediately afterward. The moths do not eat, and die naturally after one week.
The moths stay mated for about a day. After separation, the female lays eggs and the male looks for another female. Sometimes another male mates with the female before she can lay eggs. Each female will lay between 200 - 500 eggs! Put paper on the bottom of the container and remove empty cocoons as the moths emerge. The moths will lay eggs on the paper.
When the moths are dead, save the dead moths and cocoons to make display cases.
It is interesting to note that one ounce of silkworm eggs contains 40000 eggs (15000 eggs per gram). These worms will eat 3500 pounds (1500 kilograms) of mulberry leaves, and will spin cocoons which will yield 140 pounds (50 kilograms) of silk thread. It takes 1700 to 2000 cocoons to make one silk dress!
When first laid, all eggs are yellow. After three days, they will turn white if they are infertile, or turn black if they are fertile. Unless you want the eggs to hatch in two weeks, put the

black eggs in a tightly-sealed bag in the refrigerator. Eggs will remain viable in the refrigerator for about five years, and will not hatch until you remove them from the refrigerator.
1. Change mulberry leaves at least three times a day. Silkworms will not eat dried-up leaves.
2. Do not disturb the silkworms once they start to spin. If the framework for the cocoon is disturbed, then they will not make a cocoon. They will turn brown, then black, and die.
3. Do not overcrowd the silkworms. If they are too close together, they can't feed efficiently. Try to keep no more than about 30 large worms on a large cake platter.
4. Remove old leaves and frass (droppings) before mold starts to form.