Monday, August 27, 2012

Some Silk Statistics

Having just celebrated the successful raising of seven of nine caterpillars into butterflies this summer, a little perspective might be in order. Silk, that most prized of all fabrics, derives from the silkmoth, Bombyx mori. The caterpillars undergo five transformations. In the fifth of these, they cover their bodies with a dense coating of raw silk. When the larvae have developed into moths inside these silky covers, they release an enzyme that produces a hole in the silk—and incidentally also causes silk fibers to break down. For this reason, the making of silk begins before the moth is ready to emerge. The pupae are dipped into boiling water to kill them.

Each chrysalis or cocoon is formed of a single strand of silk. Yes. Not a typo. The  cocoon is about an inch in length. The thread of silk that forms it ranges in length from a fifth to more than half a mile. After the cocoons are boiled, a human must find the end of the thread by brushing the cocoon by hand. That end is then threaded into a needle affixed to a machine or a wheel. Then the unraveling begins.

Now for the statistics. It takes 3,000 to 5,000 larvae to make one pound of silk. The world produces 70 million pounds of raw silk every year—and to do so, 210 to 350 billion larvae must die so that we can dress our ladies decoratively. And we were proud to have helped seven butterflies to flutter away freely this summer. Hhmm.

To raise such large numbers of silk-covered larvae makes the white mulberry tree (Morus alba) happy; the caterpillars feed on its leaves until they go into the silk-chrysalis state. To be sure, being eaten in order to be cultivated is not necessarily an ideal sort of existence. In 2002, I learn from Wikipedia, 3,890 square miles were under white mulberry cultivation in China to support the silk trade, which is more than the areas of Delaware and Rhode Island combined or 80 percent of Connecticut’s surface.

How did I get here? We were discussing the fine threads that hold the Swallowtail chrysalides suspended from a plant stem—while the bottom is glued to the stem so well that the chrysalis gives way before the seal does. Brigitte got to talking about silk, which those suspending filaments surely are—and we realized that we knew nothing about the subject except that silk came from worms. We soon learned that these worms are caterpillars…
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My image of the white silkmoth cocoons is from Offset Warehouse (link). A very instructive site on how the actual silk extraction takes places comes from wormspit.com (link).

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