Silk, a natural fiber known for its luster, softness, and strength, has been valued for thousands of years. Its smooth texture and inherent sheen make it a desired material in textiles and various products. Understanding where this fiber comes from reveals its origins in the animal kingdom.
The Primary Silk Producer
Most commercial silk originates from the domesticated silkworm, Bombyx mori. This insect is the larva of a moth, belonging to the Bombycidae family. Due to domestication, the adult moth is flightless and lacks natural defenses, making it entirely dependent on human care.
The life cycle of Bombyx mori begins when a female moth lays hundreds of tiny eggs. These eggs hatch into larvae, commonly known as silkworms, which feed exclusively on mulberry leaves. The silkworms grow rapidly, shedding their skin four times over approximately 30 days. During their final growth stage, the larvae prepare to pupate by secreting a protein-rich fluid that solidifies into a continuous silk filament upon contact with air. This filament is then spun around themselves to form a protective cocoon.
From Cocoon to Fiber
The process of extracting silk from these cocoons is known as sericulture. Once the silkworm larvae complete their cocoons, they are harvested. To ensure a continuous silk filament, the pupae inside are stifled, usually by boiling or steaming. This process loosens sericin, a gummy substance binding the silk fibers, and prevents the moth from emerging and breaking the threads.
After stifling, cocoons are immersed in hot water to soften the sericin, allowing the silk filament to be unwound. A single cocoon can yield a continuous thread of silk 600 to 900 meters (about 2,000 to 3,000 feet) in length. Several fine filaments are then reeled together to create a single, stronger silk strand. This raw silk is processed further, often by degumming, which enhances its softness and luster, before being spun into yarn and woven into fabric.
Silk from Other Animals
While Bombyx mori is the primary source of commercial silk, other animals also produce silk. Wild silkworms, such as those that produce Tussah silk (Antheraea mylitta), are one example. Unlike mulberry silk, Tussah silk comes from silkworms that feed on various leaves, including oak and juniper. This varied diet results in silk fibers that are shorter, thicker, and naturally have a coarser texture and a beige or brownish color, distinguishing them from finer, whiter mulberry silk.
Spiders also produce silk, which they use for webs, egg sacs, and safety lines. Spider silk possesses exceptional tensile strength and elasticity, often surpassing that of steel or Kevlar. Despite these qualities, spider silk is not commercially viable for textile production. This is due to the challenges of farming spiders, as they are territorial and cannibalistic, making mass rearing difficult, and each spider produces only a small amount of silk.