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Just caught a brief chance to photograph this lady beetle before it flew away.

twicestabbed lady beetle

Most of us think of ladybugs or lady beetles as red with black spots, but these helpful beetles come in many colors, shapes and sizes. This one has the interesting name of Twicestabbed lady beetle, from the two spots of bright red on its wings (elytra), one on either side. The scientific name name is Chilocorus. Although it was only a brief glance, it is probably Chilocorus orbus, which feeds on scale insects.

Hope everyone has a nice Thanksgiving!

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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.

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Can you find the insect in these photos?

cochineal scale

cochineal scale

If you guess the white fuzzy, waxy stuff might be a clue, then congratulations. Believe it or not, the insect we are going to explore today has been the subject of greed, subterfuge and may have helped our forefathers defeat the British during the Revolutionary War. Not quite what you’d expect from a tiny insect that spends its life feeding on cactus pads hidden under some white fluff.

When the Spanish explorers first came to the New World they discovered the natives were wearing bright red garments. They were amazed, because no color like that could be found in Europe. The Mixtec people had been culturing a tiny insect, called the cochineal scale, as a way to produce a wondrous dye.

The cochineal scale insects live on the pads of certain prickly pear cacti. I’m not even sure how the early Mixtecs discovered the red body of the scale, because all you see on the surface is white fluff. Underneath is a small blob that looks like a pinkish seed. Within the body, the hemolymph is deep red. Although I doubt you can see it, there are few drops of this red where a bird or something has pulled the scale from out of the waxy covering in the left, center of the photographs. (Someday I hope to get some better photos, but this was at a public garden and I didn't want to disturb nature. As usual, The Firefly Forest has a good photo if you want to see another example.) Somehow the Mixtecs found the cochineal scale, however, and they figured out how to process them into a red dye.

The Mixtecs farmed the insects with skill and care. They would plant cactus pads infested with the scales, weed the plants, build walls to keep animals away from the plants, and even shelter the plants during rain showers so the insects wouldn’t get washed away. Then they would carefully collect and dry the female scales to make the dye powder. It was a hugely labor intensive process. Not to mention that the cactus pads were covered with painful spines, which had to be avoided.

Many people in Europe wanted the dye and there was a limited supply. At first, only the very rich and powerful could wear it, like kings and queens, or the bishops and cardinals of the Roman Catholic Church. By the year 1600 cochineal dye was an extremely valuable export from Southern Mexico. Gold was the only export from the region worth more money. Dried insect bodies were worth more than silver!

The Spanish went to great lengths to keep the origin of the dye a secret. In fact, the results of their subterfuge can still be found on the Internet today. You can find websites that mention the “cochineal beetle.” In the past, people thought the secret insect might be a beetle and this misidentification has survived until today. See this webpage, for example. Scale insects are flat, legless and have sucking mouthparts. Beetles are rounded, have hard wings called elytra, prominent legs and chewing mouthparts. Cochineals are scales for sure. Oops. And by the way, the insects make the red coloring within their own bodies, they do not obtain it from the red fruit.

Eventually the dye was used to color the “redcoats” of the British army during the Revolutionary War. I have read that our soldiers were able to recognize and selectively fire upon the high-ranking soldiers, because only the elite got to wear the bright red cochineal-dyed uniforms. The foot soldiers uniforms were dyed with a cheaper dye that gave a duller color. Thus, the officers were easy to spot.

In the 1870’s, synthetic red dyes were developed and they began to replace cochineal for widespread use. Cochineal in the United States is now largely used as a food dye, found in such products as sausages, candies, and juices, as well as cosmetics. Check some of the ingredients of pink fruit drinks at your local grocery and look for the word "cochineal." You may have been appreciating these wonderful insects when you drank juice and you didn’t even know it.