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On the theme of remarkable discoveries from humble insect beginnings, let’s explore another insect that also changed human history, the silkworm.

Legend has it that humans and silkworms met one fine morning in the year 2640 B.C. A Chinese Empress named Hsi-Ling-Chi (various other spellings found) was strolling in her garden drinking tea when a white cocoon plopped into her cup from an overhead tree.

It probably looked something like this:

silkworm cocoon

Instead of dumping it out and asking her servant for another cup of tea like any reasonable person would probably have done, she studied the cocoon. She stirred the warm tea with her finger and noticed a fine strand beginning to unravel from the fuzzy cocoon. Being a weaver, she thought of using the fiber to make cloth. She called to her servant and together they unwound the cocoon into a single long filament. Thus, the silk industry was born.

The cocoon that Hsi-Ling-Chi had collided with was that of the silkworm moth, Bombyx mori. The caterpillar feeds on leaves of mulberry trees of the genus Morus, hence the silkworm species name mori.

silkworm caterpillar

Here are some silkworm caterpillars getting ready to pupate:

silkworm caterpillar

When it is ready to transform into an adult, the caterpillar uses its enormous silk-producing glands (the glands are up to 25% of the mature caterpillar’s weight!) to spin the oval cocoon.

Rather than being soft and pliable, as you would expect from something made of silk, the cocoon is actually rigid because the caterpillar adds a sticky, gummy protein called sericin to the thread. The sericin hardens into a stiff protective coating, giving the whole thing a consistency resembling Styrofoam. Inside the cocoon, the caterpillar transforms into a pupa, and then into a buff-colored moth.

How does a moth, which does not have chewing jaws like the caterpillar, escape the hardened cocoon? Amazingly, the moth discharges a special enzyme that dissolves both the silk and the sericin in one end of the cocoon, allowing the moth to escape through a circular opening.

With her swirling tea bath, Hsi-Ling-Chi had discovered the process to free the silk from the sericin by immersion in hot water. If the moth is allowed to emerge from the cocoon naturally, the enzyme cuts through all the strands, making too many short pieces to spin easily. In the silk industry the cocoons are boiled with the pupa still inside to obtain one long strand of silk, exactly as the caterpillar laid it down. Strands from several cocoons are then spun together to make a strong thread, and woven into cloth.

The resulting silk cloth was like nothing that had been available before. It was lightweight and relatively smooth, and pleasing to the touch. The Emperor soon realized the potential of silk as a commodity and rushed into large-scale production. The Chinese began to share their product with the world, which was eager to buy it.

Although they were willing to sell the silk cloth, the Chinese carefully kept the source shrouded in mystery for well over 1000 years. The penalty for disclosing the source of silk was death. By keeping silkworms a secret, the Chinese developed one of the greatest trade monopolies ever. Wealthy Europeans and Middle Easterners wanted the silk, and the so-called Silk Road between China and Europe opened up more trade between the continents. Other products and ideas began to be exchanged as well. This exchange of goods allowed certain groups to accumulate wealth and shifted power and culture throughout the world.

Speculation about the source of silk was wild. One group thought the Chinese were harvesting silk from a new variety of animal called a sea-sheep. Others thought it came from various plants. As late as the Roman Empire, Pliny the Elder who wrote his Natural History around 70 AD, thought the source of silk was a tree. Eventually Japan, India and then the Byzantines discovered the real secret of silk and started their own silk production or sericulture programs. The Byzantines were able to undercut the Chinese after some Nestorian monks smuggled silkworm cocoons out of China in their canes. But China remained the most important source for many centuries. Eventually the Turks cut off the overland route to Asia. European exploration for alternative routes to obtain both silk and spices lead Columbus to the New World.

Early Europeans coming to the New World carried silkworms with them. The English had long wanted to develop a silkworm industry, but their climate was not suitable. The king thought that starting silkworm farms in the colonies could be a good solution and forced farmers to plant groves of mulberry trees. However, the silkworms turned out to be fussy and never did well. Farmers quickly turned to more profitable cotton and tobacco as crops.

Not only did the silkworm change our history, but we changed the silkworm too. Silkworms are now truly domesticated creatures. There are no Bombyx mori moths left in the wild. Over thousands of years of selection by humans, the caterpillars have lost all urge to crawl and sit placidly waiting for food to be dumped onto them. The moths are heavy-bodied with shortened wings, and they can do no more than flap their wings and make short hops. When we raised ours, we found that if a male moth managed to flutter out of its container, it sat there (I thought it looked embarrassed) until a person comes along to retrieve it. Silkworms now depend on humans completely for their survival. Some strains have been bred that can develop on artificial diets made of ground up dried mulberry leaves and vitamins.

Along with the changes in the people and the moths, came changes with the trees they feed on. Because the silkworm consumes leaves of the mulberry tree, particularly the white or Chinese mulberry Morus alba, the trees were spread throughout the world with the silkworms. In the United States we also have a native American or red mulberry, Morus rubra, and the black mulberry, Morus nigra, first sent over from Europe during the colonial period. White mulberries of the variety Morus multicaulis were developed for silkworm cultivation and have been distributed widely during attempts to establish a silkworm industry here. In addition to being food for silkworms, the trees produce small clustered fruit that can be used to make jams, pies and fruit spreads.

mullberry treemullberry tree

Eventually synthetic fibers were discovered that have largely replaced silk. Nonetheless, it is still a popular fabric. It takes dyes beautifully, is warm in winter, cool in summer and drapes marvelously. Today silk is still cultivated in Japan, China, Spain France, Italy and Columbia. Lady Di’s wedding dress was made of silk from Britain’s last remaining active silkworm farm. Throughout the last 4000 years wearing silk has been a status symbol of the wealthy, and the desire for it has changed history.

For more information on rearing silkworms, a step-by step look at growing silkworms can be found in the Bombyx mori on-line Journal.

Edit: For more recent photographs, see a newer post about silkworms.

Books (linked titles and images go to Amazon):

Children's Nonfiction:

Silkworms (Lerner Natural Science Books) by Sylvia A. Johnson

Silkworm (Life Cycle of a . . .) by Ron Fridell, and Patricia Walsh

The Story of Silk: From Worm Spit to Woven Scarves (Traveling Photographer)by Richard Sobol

Children's Fiction
The Empress and the Silkworm by Lily Toy Hong

Fiction Chapter Book

Project Mulberry by Linda Sue Park is a fiction chapter book about two children who decide to raise silkworms for a state fair project. Although the story about silkworms is already compelling, the main character and the author also have chats on the side throughout the book that reveal how the process of writing works.

Adult Non-fiction:

Shrinking the Cat: Genetic Engineering Before We Knew About Genes
by Sue Hubell. Houghton Mifflin Company, New York. 2001. Despite the title, she also has packed in a great deal of information about silkworms.

Science Books for Kids also has a growing list of children's books about moths and butterflies.

For those interested in butterfly gardening and caterpillars, here are a few more children’s books to consider.

2015 Edit:  For our most complete and up-to-date list of butterfly books for kids, visit  Science Books for Kids website.

moth-and-butterfly-books-for-children-list

Nonfiction

Nic Bishop Butterflies and Moths by Nic Bishop just came out and it is fabulous!

The butterfly book : a kid's guide to attracting, raising, and keeping butterflies by Kersten Hamilton.

This butterfly book for older children is full of scientific information and suggestions for activities, such as making a butterfly net. It starts out with a “getting to know” section that covers much of the complex vocabulary children will need to read this and other books about butterflies. Then the author covers many aspects of raising and keeping butterflies, as well as butterfly behavior and biology. A butterfly guide on the edges of each page has extensive photographs and accurate illustrations of common butterflies, and includes a map of where they are found. The resource guide and “glossarized index” at the end help children find out more. If you are interested in raising butterflies or butterfly gardening, this book is an excellent resource.

It's a butterfly's life by Irene Kelly.

This nonfiction book has many lovely illustrations. If you are looking for a book for a child to read, be aware that the font looks like hand lettering and the sentences wave up and down across the page, almost like the pattern of a butterfly flying. This looks lovely, but may be hard for a beginning reader to read. It has many interesting facts, and covers the butterfly life cycle in detail.

Creepy, crawly caterpillars by Margery Facklam and illustrated by Paul Facklam.

All the terms used throughout the book are defined in the text in the first two pages. The second page of this book has an absolutely amazing illustration of a caterpillar with all its parts labeled clearly and accurately. The rest of the book is two-page spreads of specific common and interesting caterpillars, for example the woolly bear and the cecropia moth caterpillar. Most of the caterpillars chosen are actually moth caterpillars, rather than butterfly caterpillars, but it is still fascinating to learn about them. This book has a glossary.

Face to face with caterpillars by Darlyne A. Murawski.

The author is a photographer who talks about how she got some of her stunning photographs next to the actual results. She starts out with the story of a caterpillar that eats ants and how she photographed the caterpillar through glass. This and some other parts of the book feels as if the photographs drove the text, rather than vice versa. There is a great deal of information on caterpillars, however, to accompany the wonderful, one-of-a-kind photographs. The end contains a glossary: a “find out more” section with articles, books and websites; an index to help children search the text; and a sidebar of research and photographic notes.

Fiction

The girl who loved caterpillars : a twelfth-century tale from Japan adapted by Jean Merrill and illustrated by Floyd Cooper.

It is hard not to love a book that is so beautifully written and illustrated. The overall tale is of a lovely young Japanese girl who defies the traditions of her time. She prefers caterpillars and centipedes to butterflies, and collects and raises them. This story is incredibly complex, and even makes adults who read it think deeply about it. One issue is the fact that the story is probably only the first chapter of a much longer tale, but the rest has been lost. Some people may wonder why the author didn’t construct her own ending. Rather than detracting from the book however, for me it only made it more interesting.

There are more butterfly book reviews at the end of the white-lined sphinx moth post.

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Wow, talk about timing. Shortly after I posted my Bug of the Week yesterday suggesting white-lined sphinx moth caterpillars (Hyles lineata) might be coming soon (see after second ladybug in that post), I got a call that masses of caterpillars are crossing Maricopa Road just South of Riggs Road, near Maricopa, Arizona. I drove right down. I probably should have taken the video camera instead of my still camera, because it doesn’t do justice to how fast these caterpillars were moving.

Unlike the pictures I linked to yesterday, these are mostly yellow and black caterpillars with a greenish head. As with many sphinx moths, the caterpillars have a spike at the tail.

whiteline caterpillar

The yellow marks below are where caterpillars didn’t make it across the road. I hope you can make out the yellow squiggles of all the caterpillars that are trying.

caterpillars in road

White-lined sphinx moth caterpillars vary considerably in color. This one was pale green rather than bright yellow.

small whiteline caterpillar

Aren’t these beauties?

caterpillar close upwhiteline caterpillar

Check the More About post for an update on white-lined sphinx moths.
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    Books About Caterpillars

If all these recent posts about caterpillars have made you interested in butterflies and moths, here are some books where you can learn more.

Books about caterpillars/butterflies for the youngest bug enthusiasts (Toddler):

The Very Hungry Caterpillar by Eric Carle
Summary: The board book version of this story is a perennial favorite. The story line is fun, the illustrations are colorful and the holes in the pages are magnets for little fingers. We made stick puppet characters and performed the story again and again.


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In depth review: As a scientist, I do have to point out one minor misuse of a term. In the end of the book (do I need to say spoiler alert here?) the caterpillar turns into a cocoon and then into a beautiful butterfly. Technically, however, a butterfly comes from chrysalis (or chrysalid), not a cocoon. Cocoons are the silken bags that moth caterpillars form around themselves prior to pupating. I see it as just a sloppy use of a word with a precise scientific meaning.

Eric Carle has been very open about admitting his mistake, although he does talk about an obscure butterfly that actually makes a cocoon. See http://www.eric-carle.com/q-cocoon.html for his response. To be fair, this book is a work of fiction. Caterpillars don’t really eat cherry pie or sausages either. That is part of what makes it so fun. So, go ahead and pick up a copy. You can read it as is, substitute chrysalis or substitute the word pupa if you don’t want to say chrysalis.

Caterpillar’s Wish by Mary Murphy is another colorful picture book about a caterpillar that turns into a butterfly. It is a delightful story about three friends. Bee and Ladybug can fly, but Caterpillar can’t. Caterpillar feels left out until he transforms into a butterfly.


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In depth: Once again the author has chosen to call the transitional stage a cocoon. In this case it may be because cocoon is a smaller word, more appropriate for toddlers? (Perhaps authors of children’s books should use the more generic word “pupa.” It is short, easy to say and always correct, regardless of which insect is the subject.)

Inch by Inch by Leo Lionni is an adorable tale of an inchworm that escapes from some hungry birds in a clever way. This book could also be useful as an introduction to measuring.


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Waiting for Wings by Lois Ehlert is bright, bold and beautifully done. It traces the life cycle of a butterfly very simply, and then has a bit more in depth information about butterflies and flowers at the end. There’s even a page of information about butterfly gardening.

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Ten Little Caterpillars
by Bill Martin Jr. and illustrated by Lois Ehlert

From Caterpillar to Butterfly by Deborah Heiligman, and illustrated by Bari Weissman, is an account of a classroom caterpillar that undergoes metamorphosis into a beautiful butterfly.

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Caterpillarology
by Michael Elsohn Ross is for children who are interested in science and doing science experiments. This book (and the others in the “-ology” series) are chock full of great information and fun activities. Whereas many children’s books repeat the same information over and over, these books are truly unique and interesting. “Chosen by Science Books and Films as one of the Best Books for Children.” Unfortunately, they are often out of print and may be hard to find.

See our growing list of children's books about moths and butterflies at Science Books for Kids.