Yes, silk comes from worms, though “worm” is a bit of a misnomer. The creatures that produce silk are actually caterpillars, the larval stage of a moth called Bombyx mori. These caterpillars have been called “silkworms” for thousands of years, but they’re insects, not true worms. Each one spins a cocoon from a single continuous thread of silk protein that can stretch 600 to 900 meters long.
Silkworms Are Caterpillars, Not Worms
The domestic silk moth, Bombyx mori, belongs to the moth family Bombycidae. Its closest wild relative is Bombyx mandarina. The “silkworm” is simply the larval (caterpillar) stage of this moth’s life cycle, the phase between hatching from an egg and forming a cocoon to pupate. True worms, like earthworms, are an entirely different category of animal. The name “silkworm” stuck because the caterpillars are small, pale, and somewhat worm-like in appearance.
Humans have been raising these caterpillars for silk production for at least 5,000 years, starting in China and eventually spreading to India, Korea, Japan, and beyond. The practice is called sericulture. After millennia of selective breeding, domestic silkworms are now completely dependent on human care. They can’t survive in the wild, and the adult moths can no longer fly.
How a Caterpillar Makes Silk
Silkworms have a pair of specialized silk glands that are remarkably efficient at producing protein. During the final stage of larval development (called the fifth instar), these glands can synthesize 20 to 35 percent of the caterpillar’s own body weight in protein in roughly one week. The silk starts as a liquid protein solution with an extremely high concentration, around 30%, inside the gland. Modern textile engineering still can’t replicate this process artificially.
The caterpillar pushes this liquid through a small opening near its mouth called a spinneret. As the protein hits the air and is stretched, it solidifies into a fiber. The fiber has two main components: a strong inner core and a gummy outer coating that acts like glue, holding the cocoon together. The caterpillar moves its head in a figure-eight pattern, wrapping itself in layer after layer until the cocoon is complete. Inside this protective shell, it transforms into a pupa and, if left undisturbed, eventually emerges as a moth.
From Cocoon to Fabric
Commercial silk production interrupts the moth’s life cycle. Cocoons are harvested before the moth emerges, because hatching breaks the continuous thread into shorter, less useful pieces. The harvested cocoons then go through a multi-step cooking process to soften the gummy coating so the thread can be unwound.
In modern factories, this starts with soaking the cocoons in warm water at about 55°C to swell the outer layer. Then the cocoons are exposed to steam at 90 to 95°C, which forces water into the cocoon cavity and heats it evenly from outside in. A gradual cooling phase stabilizes the softened coating. After cooking, workers or machines find the end of the filament and reel it off the cocoon in one long, continuous strand. Several of these ultra-fine strands are twisted together to form a single thread strong enough for weaving.
The gummy coating is later removed by boiling the raw thread in a mild alkaline solution, leaving behind the pure silk fiber that gives the fabric its characteristic sheen and softness.
Other Types of Silk-Producing Caterpillars
Bombyx mori produces the vast majority of the world’s commercial silk, but it’s not the only species people use. A separate moth family, Saturniidae, includes caterpillars of the genus Antheraea that produce what’s known as “wild silk.” Muga silk, for example, comes from Antheraea assamensis, a caterpillar found in northeastern India that feeds on specific laurel-family trees and produces a naturally golden-colored thread. Tussar and Eri silk come from other related species. These wild silks tend to have a coarser texture and different sheen than mulberry silk from Bombyx mori.
China remains the world’s largest silk producer and the dominant supplier to global markets. India ranks second. Uzbekistan, Brazil, Thailand, and Vietnam also contribute to global production.
Peace Silk: A No-Kill Alternative
Conventional silk production kills the pupa inside the cocoon, typically within about 15 minutes of the cocoon being completed. This has led to the development of “peace silk,” also called Ahimsa silk, which takes a different approach. Instead of harvesting cocoons immediately, producers wait roughly 10 additional days for the moth to fully develop and emerge on its own. The moth breaks through the cocoon wall using a special enzyme, leaving a small hole.
That hole is exactly the trade-off: it breaks the continuous filament, so the silk must be spun from shorter fibers rather than reeled in one long strand. This produces a slightly different texture and requires more labor. In some cases, experienced workers carefully cut cocoons open at just the right moment to minimize fiber loss while still allowing the pupa to survive. Peace silk costs more and has a different feel than conventional silk, but it offers an option for people who want the fabric without the ethical concern.