The term “green silkworm” refers to several species of silkworms that produce naturally green silk cocoons or have green-colored larvae. Unlike the more widely known domesticated silkworm, Bombyx mori, which typically produces white or yellow silk, these green varieties are often wild or semi-domesticated. One prominent example is the Japanese tasar silkworm, Antheraea yamamai, known for its distinctive green silk thread. Other wild silkworms, such as the Io moth larvae, can also exhibit a yellowish or bluish-green coloration. These insects belong to the broader family Saturniidae, known as giant silkworm and royal moths.
The Unique Reason for its Green Hue
The green coloration in certain silkworms and their silk is directly linked to their diet. These silkworms consume specific plant leaves, such as sawtooth oak, which contain chlorophyll. The chlorophyll is then absorbed and metabolized, allowing the pigment to be incorporated into their tissues and the silk they produce.
Unlike domesticated silkworms like Bombyx mori, which lost pigmentation due to selective breeding, wild green silkworms retain natural colors for camouflage. The green color is not a surface stain but results from the direct uptake of chlorophyll and related metabolites, integrated into the silk protein structure. This differs from artificial coloring methods, where dyes are sprayed on leaves.
Life Stages and Natural Home
The life cycle of a green silkworm, similar to other silkworms, involves four main stages: egg, larva, pupa, and adult moth. A female moth lays hundreds of tiny eggs, which typically hatch into larvae, commonly known as silkworms. These larvae are voracious eaters, consuming large quantities of leaves, such as sawtooth oak, for approximately 20 to 35 days, during which they grow significantly and molt several times.
After reaching their full size, the larvae transition into the pupal stage, forming a protective cocoon around themselves. This cocoon is spun from a continuous silk thread produced by their salivary glands, and in the case of green silkworms, this thread is green. The pupal stage can last about ten days, after which the adult moth emerges from the cocoon. The adult moths generally live for a short period, typically 3 to 10 days, primarily focusing on mating and laying eggs.
Green silkworms, particularly species like Antheraea yamamai, are found in specific natural habitats. The Japanese tasar silkworm is peculiar to Japan, thriving where its preferred host plants, such as oak leaves, are abundant. These wild silkworms survive independently of human care, foraging on a wider variety of trees than domesticated silkworms. The sawtooth oak fields at the foot of the Northern Alps in Azumino City, Japan, are a suitable location for these wild silkworms.
Beyond the Common Silkworm: Special Traits and Applications
The green silkworm differentiates itself from the common domesticated silkworm, Bombyx mori, in several ways. While Bombyx mori has been selectively bred over millennia for high silk production and has lost its ability to fly and much of its natural pigmentation, many green silkworm species are wild or semi-domesticated, retaining their natural colors and behaviors. For example, Antheraea yamamai is a wild silkworm that feeds on oak leaves, producing a unique green silk thread.
The silk produced by these green silkworms possesses distinct characteristics. Antheraea yamamai silk, often called “fiber diamond” due to its brilliant luster, is naturally glossy and green. While a single cocoon from domesticated silkworms can yield up to 1,500 meters of raw silk, wild silkworms like Antheraea yamamai produce less, around 700 meters per cocoon. Despite the lower yield, the rarity and natural beauty of wild green silk make it highly valued, especially for traditional textiles like Shinshu Tsumugi in Japan, known for its lightness and durability.
Beyond textiles, the unique properties of silkworm materials, including those from green varieties, are explored in various scientific and research fields. Silkworm silk, with its excellent biocompatibility and mechanical properties, has applications in biomedical research, such as surgical sutures, drug delivery systems, and tissue engineering. The protein components of silk, fibroin and sericin, are particularly valuable. Research also investigates the potential of silkworm extracts for medicinal uses, such as improving iron deficiency anemia.