While it's pretty clear to most people why vegans don't eat meat or wear fur, why they don't wear silk is less obvious. Silk fabric is made from the fiber that's spun by silkworms when they form the cocoons for their pupal stage prior to becoming moths. In order to harvest silk, many silkworms are killed. While some methods of silk production do not require the creatures to die, it's still a form of animal exploitation. Since vegans do not use products they believe exploit animals, they do not use silk.
How Is Silk Made?
Mass-produced silk is made from domesticated silkworms, Bombyx mori, that are raised on farms. These silkworms-the caterpillar stage of the silk moth-are fed mulberry leaves until they are ready to spin cocoons and enter the pupal stage. The silk is secreted as a liquid from two glands in the caterpillar's head. While in the pupal stage, the cocoons are placed in boiling water, which kills the silkworms and begins the process of unraveling the cocoons in order to produce silk threads.
Approximately 15 silkworms are killed to make a gram of silk thread, and 10,000 are killed to make a silk sari. If allowed to develop and live, the silkworms would turn into moths and chew their way out of the cocoons to escape. However, these chewed silk strands are much shorter and less valuable than the whole cocoons.
Silk thread can also be produced by killing silkworms while they are in the caterpillar stage, just before they spin 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.
Non-Violent Silk Production
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 that 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 as Bombyx mori silk. Instead, it is carded and spun like wool. Unfortunately, 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. Due to the broken strands, less of the silk is usable for textile production, so Ahimsa silk costs more than conventional silk. "Ahimsa" is the Hindu word for "non-violence." Ahimsa silk, though popular with the followers of Jainism, also represents a very small portion of the silk market.
Do Insects Suffer?
Dropping silkworms into boiling water kills them, potentially causing them to suffer. While the insect nervous system differs from that of mammals, insects do transmit signals from stimuli that cause a response. Experts disagree over how much an insect can suffer or feel pain. Most, however, leave the door open to the question and believe it may be possible that insects feel something akin to what we would classify as pain.
Even if you accept the premise that insects don't feel pain in the same way that humans or even other animals experience it, vegans believe that all creatures are deserving of humane treatment. While it may not technically "hurt them," when a silkworm is dropped into boiling water, it dies-and death free of pain is still death.
Why Vegans Don't Wear Silk
Vegans try to avoid harming and exploiting animals, which means they do not use animal products, including meat, dairy, eggs, fur, leather, wool-or silk. Since vegans consider all insects sentient, they believe these creatures have an animal right to a life free of suffering. Even the harvesting of Eri silk or Ahimsa silk is problematic because it involves 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 mouthparts. Similar to cows that 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 possible 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 longer. 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.