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  • Richard Conniff writes about behavior, in humans and other animals, on two, four, six, and eight legs, plus the occasional slither.

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The Disturbing Things We Do For Silk

Posted by Richard Conniff on September 25, 2013

Silkworm cocoons ready to be processed into silk (Photo: John Javellana/ Reuters)

Silkworm cocoons ready to be processed into silk (Photo: John Javellana/ Reuters)

The latest research on silkworms is wonderful news on the fashion front, opening up the possibility for new textiles and more efficient manufacturing methods. But for the silkworms, it also sounds kind of creepy in a science fiction nightmare way.

First, a little background. Humans have had a long and rewarding relationship with the Chinese mulberry silkworm Bombyx mori, ever since someone figured out 6,000 years ago how to unravel the threads from the caterpillars’ cocoons and weave them into gorgeous textiles for China’s emperorsThe Chinese managed to keep the process secret for centuries, until it became the object of history’s first known instance of commercial espionage. In the sixth century A.D., according to legend, the European emperor Justinian dispatched two monks to China. They returned with both the silkworm eggs and seeds for the mulberry trees on which they feed, smuggled home inside bamboo walking sticks.

The result today is a global industry. China is once again leading the world, producing 58,000 tons of silk annually. (And that is a lot of caterpillars.) The United States also had a thriving silk industry, until the introduction of nylon in World War II. My family was among the many that benefited from it: My grandfather was a warper at silk mills in Manchester, Connecticut, and Paterson, New Jersey. So without silkworm wages—not to put too fine a point on it—there would be no me.

Now back to the new research, just out in the journal Biomacromolecules. British researchers have devised a means to continuously milk silk from living silkworms. This is a big deal because of an unfortunate fact behind the loveliness of silk: Up to now, the only way to unravel silk was to boil the cocoons, killing the silkworms inside. Mohandas Gandhi criticized the process, as have modern animal rights activists. But when researchers tried to extract the silk more directly, the caterpillars resisted, clamping onto the line and snapping it. The record for reeling a strand of silk out of a living caterpillar was just six meters.

The researchers in the new study noticed that silkworms employ a “play dead” behavior, lingering in a state of self-induced paralysis when injured. Otherwise, the caterpillar’s way of moving—picture the classic inchworm—would cause hydrostatic pressure and further tear the wound. Alex Wood, a physician and entomologist, identified the chemical the caterpillars rely on. By injecting it into caterpillars, researchers at Oxford University were able to induce a state of semi-paralysis.

The resulting production technique could make buying silk acceptable again, for people who have balked because of that business about boiling. Even so, the new technique doesn’t make a pretty picture: The caterpillar is attached to a stick and suspended in mid-air, like one of the unconscious organ donors in the science fiction movie Coma. One end of the silk that the worm is producing becomes attached to a reel, which slowly winds it up, keeping time with the caterpillar. In its semi-conscious state, the caterpillar may realize what’s happening. And it may not like it. But paralysis means that it is too weak to snap the wonderfully strong silk that it is producing. So far, the researchers have been able to extract silk from a single caterpillar for up to six hours, and a record of 500 meters.

The press release for the new study touts the discovery as the key to manufacturing a variety of new silk products, including medical implants (as in Coma). It also highlights “the exciting potential for genetically modifying silkworms to induce paralysis ‘on-demand,’ a particularly useful feature for mass-rearing.”

But to be honest, I think I’m going to have bad dreams tonight. You know the kind—lying there paralyzed while strangers move around in the shadows.

I suppose, though, that it is at least a step up from being boiled alive.

5 Responses to “The Disturbing Things We Do For Silk”

  1. But in the end the caterpillar is killed anyway.

    • Ah, I was hoping they put them out in the mulberry pasture. Does it say they kill them in the journal article? I missed that. Or are you just inferring that it would be too impractical to allow them to reach their adult stage?

      • Well, they pull out the silk that would be otherwise used to spin a cocoon. Pupae usually dry out without protection. Also, you are right: it would be impractical to raise them all to adult stage, since each female lays dozens of eggs, so only a small percentage is used for breeding.

  2. Richelle said

    Touche. Solid arguments. Keeep uup thhe greeat effort.

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