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Secrets of silk: an ancient mystery reaches the end of the road.

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The people of ancient Rome faced a mystery: Traders returned from the East with a fine, shimmering cloth like nothing else they had ever seen. It was silk. This strong but soft material kept wearers cool in hot weather and warm in cold weather.

Roman citizens, from the lowest classes to the Emperor himself, were soon hooked on silk, paying high prices for the luxurious material while they tried to figure out how to produce it themselves. Because they made other cloths from plants, such as flax and cotton, they mistakenly thought silk came from a plant too. Read on to see why silk-making was so mysterious and how the secret finally got out.

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AN ANCIENT MYSTERY

Romans didn't have direct contact with the people who manufactured silk. The glistening material came from China via the Silk Road, a network of trading pathways stretching from Asia through the Middle East and Europe. On these pathways, camel caravans carried goods across terrain that included harsh deserts and high mountains. But merchants didn't travel the whole route. Goods moved through a series of middlemen. "People would take their goods a couple hundred miles; they'd trade it for other things, and then they'd go back in the other direction," says Mark Norell, curator of the exhibition Traveling the Silk Road at the American Museum of Natural History in New York City. "So not only did the people at the ends of the Silk Road not know what the people at the other end looked like, they didn't even know where the goods came from."

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China's rulers guarded the secret of sericulture, or silk production, with extremely harsh penalties. Norell says, "They had a virtual monopoly on making silk during this time period, so much so that it was a penalty of death if you shared silk-making secrets with foreigners." When Romans looked to plants for the answer, they were barking up the wrong tree. At the other end of the Silk Road, tiny creatures were spinning the mysterious fabric.

CRAFTY CATERPILLARS

The Chinese discovered the secret--that caterpillars spin cocoons of silky filaments--at least 5,000 years ago. Through selective breeding of moths with the desired traits, they developed a domestic species of silk moth (Bombyx mori) whose caterpillars produce smoother, finer filaments. These moths are blind and flightless, and can survive only under the care of silk farmers. Each female moth lays up to 500 pinpoint-size eggs before dying.

Caring for the creatures was a time-consuming project for China's women, who handled most of the sericulture. They placed the eggs in shaded trays to keep them at the right temperature. Ten to 12 days later, the larvae, in the form of tiny caterpillars commonly called silkworms, crawled out. To feed these picky eaters, who munch around the clock, the women chopped the silkworms' favorite food: mulberry leaves. The caterpillars molted, or shed their skin, as their weight multiplied 10,000 times in one month. Workers carefully protected these fragile creatures from drafts, loud noises, and even strong odors.

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After several caterpillar molts, farmers set up frames of twigs. Each caterpillar climbed a twig and secreted a silk thread from its spinneret (tube in its mouth). The thread is made of two strands of fibroin. Fibroin is a protein (substance made of chains of chemicals called amino acids) that is produced by a pair of silk glands. These glands also produce another protein, sericin, that glues the two threads together as the silk hardens in the air. The result: a white, puffy cocoon made of a single filament 600 to 900 meters (1,970 to 2,950 feet) long.

END OF THE LINE

Normally, the pupae inside the cocoons would transform into moths. But silk farmers couldn't let that happen. Norell explains: "If it changes into a moth, the threads are broken as the animal climbs out." So the farmers killed the pupae by baking or steaming the cocoons, or soaking them with salt water. Then they dumped the cocoons into boiling water to remove the sericin and loosen the filament.

Workers wound filaments from roughly five to eight cocoons on a wheel to make a single silk thread, then rewound them to make them finer. They wove the finished threads into cloth. To get enough silk for one robe, farmers had to successfully raise 2,500 caterpillars.

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TIMELESS TECHNOLOGY

The Silk Road reached its peak during China's Tang dynasty (618 to 906 A.D.) as a trading network not only for silk but also for many other goods, technologies, and ideas. "Just about everything that could be traded was traded," Norell says.

The practice of sericulture gradually spread to other lands. In 552 A.D. the secret reached Europe through two monks who, as the story goes, smuggled silk moth eggs inside hollow bamboo walking sticks. But the highest-quality silk still came from China.

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After thousands of years, the steps for producing silk haven't changed. "Quite a bit of it has been mechanized, but the basic principles of it are still identical: You're growing the silkworms and then boiling the cocoons, and then pulling the threads off the cocoons and spinning those into more usable, consistent threads," says Norell. When you wear a silk shirt, camp with a silk-lined sleeping bag, or put silk sheets on your bed, you're benefiting from an ancient technology that is popular even in today's modern world.

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check it out

Experience adventure from a thousand years ago through Traveling the Silk Road: Ancient Pathway to the Modern World. This new exhibition at the American Museum of Natural History opens November 14, 2009, and features models of life-size "boats of the desert," better known as camels. Camels sweat very little but can lose up to 30 percent of their weight in water... and can then slurp it all back in less than 15 minutes. Learn more about camels and ancient trade routes by asking your teacher or visiting www.amnh.org

web extra

For more Science Explorations content, visit: www.scholastic.com/scienceworld

PRE-READING PROMPTS:

* What is silk?

* What kinds of things do you own that are made from silk?

* Where do you think silk comes from?

DID YOU KNOW?

* In 2008, the full genome of the silkworm was published by the International Silkworm Genome Consortium. The genome contains 530,000,000 base pairs, which is approximately one sixth the size of the human genome.

* Korean street vendors sell a food called beondegi, which is made from seasoned silkworm larvae that are steamed or boiled.

* According to the United Nation's Food and Agriculture Organization, China has more than 6,000 square kilometers (2,317 square miles) of land dedicated to cultivating mulberry trees, which feed the country's silkworms. That's more space than the landmass of the state of Delaware!

CRITICAL THINKING:

* Silk is produced by caterpillars and then used in clothing, parachutes, home furnishings, and many other items. Can you think of other animals that produce materials that humans can make use of? For what type of manufactured products could these different materials be used?

CROSS-CURRICULAR CONNECTIONS:

GEOGRAPHY: Silk has a rich history and is woven throughout all the cultures that interacted along the Silk Road. Split the class into three groups and assign an explorer to each of them: Zhang Qian, Xuan Zang, and Marco Polo. Have the groups use the interactive maps on the Web site below to see which climates, languages, and belief systems the explorers encountered on their journeys. Web site: http://virtuallabs.stanford.edu/silkroad/SilkRoad.html.

RESOURCES

You can access these Web links at www.scholastic.com/scienceworld.

* For everything you could ever want to know about silkworms, visit this Web site from the University of Arizona. It has information sheets, lesson plans, tips for raising silkworms, and more! http://insected.arizona.edu/silkinfo.htm.

* Check out this online exhibit about the art and history of the Silk Road from the University of Washington: http://depts.washington.edu/silkroad/exhibit/index2.html.

* Find out more about the mulberry tree, which is the main food for silkworms, here: http://faculty.ucc.edu /biology.ombrello/POW/mulberry_tree.htm.

DIRECTIONS: Answer the following questions in complete sentences.

1. What is the Silk Road?

2. What was the heavily guarded secret of silk, and what was the penalty for sharing the secret with foreigners?

3. Why did ancient sericulture practitioners use selective breeding? What was the result?

4. What are the two proteins that a silkworm produces from its spinneret, and what are their functions?

5. How similar is modern sericulture to ancient sericulture? Explain.

Answer

1. The Silk Road is a network of trading pathways stretching from Asia through the Middle East and Europe.

2. The secret was that silk is produced by silk moth caterpillars that spin cocoons of the silky filaments. The penalty for sharing this secret with foreigners was death.

3. Ancient sericulture practitioners used selective breeding to get traits they desired in the silkworms. They raised silkworms that produced finer, silkier filaments and caterpillars that are blind and flightless so that they would rely upon the farmers to live.

4. The two proteins silkworms produce from their spinnerets are fibroin, which makes up the thread, and sericin, which glues together the fibroin strands that a silkworm produces.

5. Modern sericulture is still very similar to ancient sericulture. The basic steps are the same, but machines are now used to aid some of the steps.
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Article Details
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Title Annotation:LIFE: LIFE CYCLES
Author:Adams, Jacqueline
Publication:Science World
Geographic Code:4EUIT
Date:Oct 26, 2009
Words:1591
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