What is Silk?
Silk fabric is made from the silk that is spun by silkworms when they form the cocoons for their pupal stage, before becoming a moth. Vegans do not wear silk because it is an animal product that results from the exploitation of animals.
How is Silk Made?
Mass-produced silk is made from domesticated silkworms, Bombyx mori, raised on farms. The silkworms, who are in the caterpillar stage of the silk moth, are fed mulberry leaves until they are ready to spin cocoons and enter their pupal stage. The silk is secreted as a liquid from two glands in the caterpillar's head. While they are still in their pupal stage, the cocoons are placed in boiling water, which kills the silkworms and begins the process of unraveling the cocoons to produce silk thread.
If allowed to develop and live, the silkworms would turn into moths and chew their way out of the cocoons to escape. The chewed silk strands would be much shorter and less valuable than the whole cocoons.
Other Methods of Silk Production
Silk thread can also be produced by killing silkworms while they are in their caterpillar stage, just before they spin their cocoons, and extracting the two silk glands. The glands can then be stretched into silk threads known as silkworm gut, which is used mainly to make fly fishing lures.
Silk can also be made without killing the caterpillars. Eri silk or "peace silk" is made from the cocoons of Samia ricini, a type of silkworm who spins a cocoon with a tiny opening in the end. After metamorphosizing into moths, they crawl out of the opening. This type of silk cannot be reeled in the same way that Bombyx mori silk is reeled, and instead is carded and spun like wool. Eri silk represents a very small portion of the silk market.
Another type of silk is Ahimsa silk, which is made from the cocoons of Bombyx mori moths after the moths chew their way out of their cocoons. Because of the chewed-through strands, less of the silk is usable for textile production and Ahimsa silk costs more than conventional silk. "Ahimsa" is the Hindu word for "non-violence." Ahimsa silk, though popular with Jains, also represents a very small portion of the silk market.
Why Don't Vegans Wear Silk?
Vegans try to avoid harming and exploiting animals, which means that vegans do not use animal products, including meat, dairy, eggs, fur, leather, wool or silk. Dropping silkworms into boiling water kills the worms and probably causes them to suffer (see below). Even eri silk or Ahimsa silk are problematic because they involve the domestication, breeding and exploitation of animals. Adult Bombyx mori silkmoths cannot fly because their bodies are too big compared to their wings, and adult males cannot eat because they have underdeveloped mouth parts. Similar to cows who have been bred for maximum meat or milk production, silkworms have been bred to maximize silk production, with no regard for the well-being of the animals.
To vegans, the only possibly ethical way to produce silk would be to collect cocoons from wild insects after the adult insects emerge from them and don't need them any more. Another ethical way to wear silk would be to wear only second hand silk, freegan silk, or old pieces of clothing that were purchased before one went vegan.
Are Insects Sentient?
While experts disagree over how much an insect can suffer or feel pain, most at least leave the door open on the question, and believe it is possible that insects feel something that we would call pain if we could know what an insect feels. An insect's nervous system is different from a mammal's, but it is a nervous system that transmits signals from stimuli and causes the insect to respond to stimuli, just as a human nervous system does. They avoid unpleasant situations, whether it is a predator or uncomfortable heat. As Alan Dawrst wrote, paraphrasing Alun Anderson, Editor-in-Chief at New Scientist, "Just by studying human neurophysiology from the outside, would we conclude that people are conscious? Or would we conclude they're just executing responses without awareness?"
While Debbie Hadley, the About.com Guide to insects, concludes that insects do not feel pain, at least not in the same emotional way that humans experience pain, she believes they are still deserving of humane treatment.
Even if insects do not feel pain when dropped into boiling water, a death free of pain is still a death. Death penalty opponents focus not on the suffering or pain involved with the process, but the loss of life, which in itself is the ultimate loss.
Regardless of the extent to which insects are sentient, conscious or emotional, avoiding silk is a very small step to take to prevent thousands of animals from possibly suffering and certainly dying.