Bombyx mori

The domestic silk moth, scientifically named *Bombyx mori*, is a specialized insect species.

It belongs to the family Bombycidae and is the closest relative of the wild silk moth, *Bombyx mandarina*. While the wild species lives in the forests of northern India, China, Korea, Japan, and Russia, *B. mori* exists only because of human care. Through millennia of selective breeding, these moths have become entirely dependent on humans for reproduction and survival. They are the primary producers of silk, a material of immense economic value. This makes them one of the most important insects in human history.

The life cycle of the silk moth begins with the eggs. After about 14 days, these eggs hatch into larvae, which we call silkworms.

These larvae primarily eat the leaves of the white mulberry tree. They are attracted to a specific mulberry odorant called cis-jasmone. As they grow, the larvae go through five distinct stages called instars. After molting four times, their bodies turn slightly yellow and their skin becomes tight. To prepare for the next stage, the larvae use their salivary glands to spin a cocoon made of raw silk.

This cocoon provides a protective layer while the insect undergoes a motionless pupal state.

There are different types of silk moths categorized by how often they produce young, known as brood frequency. Univoltine silk moths produce only one brood per season. These are generally found in and around Europe, where the eggs must hibernate through the winter. Bivoltine varieties are common in East Asia. Their warmer climates allow for an accelerated breeding process. Finally, polyvoltine silk moths live in the tropics. Their eggs hatch within 9 to 12 days, allowing for up to eight generations of larvae in a single year. The development of these larvae can be influenced by environmental factors like temperature, humidity, and photoperiod, which can trigger diapause, or a physiological arrest in development.

The history of silk production, known as sericulture, is very long.

Archaeological evidence suggests domestication began with the Yangshao culture in northern China over 5,000 years ago. It is believed that breeding likely began during the Neolithic period, once humans developed the tools to manufacture silk thread. From China, sericulture spread to India, Korea, Nepal, and Japan before reaching the West.

Today, the industry is massive. Nearly 10 billion cocoons are used each year to produce at least 80,000 tons of raw silk.

Harvesting silk involves a specific and controversial process. A single silk thread is incredibly fine, measuring about 10 micrometers in diameter.

If a moth is allowed to emerge from the cocoon, it releases proteolytic enzymes. These enzymes break down the long silk fibers into much shorter, random segments. To prevent this and keep the silk threads long and valuable, the cocoons are boiled in water. This heat kills the pupa inside but makes the silk easier to unravel. Because this process kills the insect, it has been criticized by animal rights activists. This led to the creation of "Ahimsa silk," which is made from wild cocoons where the moths are allowed to emerge naturally.

As adults, *Bombyx mori* moths look very different from their wild ancestors. They have white, hairy bodies and a wingspan of about 40 to 50 millimeters.

However, they have lost their natural coloration and their ability to fly. Their bodies are often too heavy for their small wings to achieve sustained flight. Additionally, adult moths have reduced mouthparts and do not feed. Because they cannot fly to find mates, humans must assist them in the breeding process. This loss of natural traits is a direct result of being domesticated for human use.

Beyond fabric, silkworms are vital to modern science as model organisms.

Scientists use them to study genetics, hormones, and even pheromones. For example, researchers identified the first known pheromone, bombykol, by studying 500,000 individual moths. Today, researchers are exploring genetic engineering to make silkworms produce spider silk or even pharmacological drugs. In one experiment, scientists even used 6,500 silkworms to weave a silk pavilion. This shows how the unique properties of silk can connect biology with engineering and medicine.