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The book, Silkworms, by Sylvia Johnson, provides a tremendous amount of information about silkworms.  Purchasing information can be found in the Teacher Resources section of this web site.  This web site merely supplements information found in her book.  Buy a copy of the book.  It's very cheap, has amazing pictures, is very well-written, and is perfect for elementary and secondary schools. 

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 is split and used for grasping twigs and leaves.  All 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 several times while growing.

Are silkworms cold-blooded?
The only warm-blooded animals alive today are mammals and birds. All living 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.

The difference between warm-blooded and cold-blooded:
A warm-blooded animal always has the interior of its body at the same temperature (98.6 degrees 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 varies widely and is usually within a few degrees of the air around it.  On a cold winter day, a cold-blooded animal's temperature may be around 40 degrees F, and on a hot day it may soar to 90 degrees F.  It doesn't bother the cold-blooded animal a bit.

On warm days, a cold-blooded animal's muscles will be warm, so it can move easily.   On a cold day, when its muscles are very cold, it will become lethargic and sluggish.  Rattlesnakes in cold areas actually hibernate during the winter since they become too sluggish to move.  Bees cannot fly when their muscles are too cold.   Bees in cold areas warm up their flight muscles by shivering until they are warm enough to sustain flight.

Scientists are still arguing about whether dinosaurs were warm- or cold-blooded.

How can you tell if a silkworm is male or female?
I don't know how to tell the caterpillars apart, but the moths are easy once you know what to look for.  The smallest caterpillars, which make the smallest cocoons, turn into males.  The big caterpillars turn into females.  The in-between ones can go either way.  Male moths are smaller, and have a flap of skin at the rear.   Females periodically extrude a scent gland out the rear.  Look at the pictures in Sylvia Johnson's book (see Teacher Resources) for close-up photos to help you tell them apart. 

It takes more energy to make eggs than to make sperm since the eggs are so much larger.   The larger caterpillars have more energy, so they become females.  The small caterpillars, in order to maximize their contribution to the gene pool, become males so they can (hopefully) impregnate lots of females. 

What is the Latin (scientific name) for the silkworm?
Bombyx mori. Bombyx means silkworm, and Mori is the possessive form of the black mulberry tree.

Why are some cocoons yellow while others are white?
It's genetic.  Some people have blue eyes and others have brown eyes.  Almost all commercial varieties of 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, you get mostly yellow offspring and a few white offspring.  When you have a mom with blue eyes and a dad with brown eyes, some of their children will have brown eyes and others will be blue-eyed.  Same idea.  With people, brown eyes are dominant.  With silkworms, the colored silk is dominant over white. 

Wild silkworms all make yellow silk, to blend in with dead leaves.  Over the centuries, silkworm farmers selectively bred for whiter and whiter silk until they achieved the pure white we see today.  They like white because it can be dyed any color without having to bleach it first.  Nowadays, with natural and organic products gaining in popularity, people are beginning to selectively breed for colored silks.  I propagate eggs for white, yellow, orange and green silk.  Cotton farmers have recently begun to breed for colored cottons and have a wide variety of naturally-colored cottons, including yellow, pink, pale-green and orange.

Why are some silkworms striped and others solid white?
They are all the same species of silkworm.  These minor color variations are like people having different color hair and eyes.  You inherit them from your parents, but we're all the same kind of people.

What do silkworm moths eat?
Silkworm moths don't eat (or drink) anything.  They mate, the female lays eggs, and then they die within 3-6 days.  Many different types of insects follow this pattern.  The mayfly is another example.  Almost all adult butterflies and moths have digestive tracts adapted for sipping nectar from flowers.  However, silkworm moths do not feed.   They still have a 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 tiny little brain.  The adult silkmoth has a more advanced brain. 

Tell me about the body segments of the silkworm.
The silkworm's body is divided into 13 segments, plus the head.  I am not aware of special names for these segments.  I'd love to have more information about this subject.  Send me an email if you know more, please!

What is that little horn on the tail end of the silkworm?
Many types of caterpillars have sharp horns or prickly hairs.  This makes predators avoid trying to eat them.  Silkworms have a soft growth that looks like a sharp horn, but if a predator tried to eat it, the growth wouldn't bother them.  But the predators don't know that!  The wild ancestors of silkworms that had these growths got eaten less often than those without the growths, so they reproduced more.  That's why modern silkworms have "horns".

How far can silkworms smell?
Silkworms have no sense of smell.  Wild adult male silkmoths have an acute sense of smell, but I don't know how far they can smell. I've never seen it in a book or tested it. From personal experience I know that a domestic silkworm male can notice a female silkworm at the opposite end of a large gymnasium, but never have tested a larger distance. I suspect that 1/4 mile would be the limit for a wild silkworm moth (downwind), but I bet that domesticated silkworms have lost much of that sensitivity since they were bred for silk, and natural selection no longer requires them to have any sense of smell whatsoever.   Adult female silkmoths also have a sense of smell, but I don't know what they use it for.

How many chromosomes does a silkworm have?
They have 54 chromosomes, which is 27 pairs of chromosomes.

Just before my silkworm spun its cocoon, It excreted a wet green or amber-colored mass.  What is it?
Just before the silkworm spins its cocoon, it makes a large "poop" to clear all the stuff out of its intestines. Once it spins the cocoon, it doesn't want to poop inside the cocoon, so it empties itself out before spinning the cocoon.   

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