How Do Silkworms Produce Silk

by Elizabeth / Wednesday, 19 April 2023 / Published in Sericulture

Silkworms, the larvae of silk moths, are nature’s remarkable textile artisans, spinning luxurious silk fibers through a fascinating biological process that involves specialized glands and intricate spinning techniques.

1. The Silk Gland: Nature’s Fiber Factory

The secret to silk production lies within the silkworm’s silk glands. These paired, modified salivary glands, located along the length of the silkworm’s body, are responsible for synthesizing and storing the liquid silk protein, fibroin.

Fibroin is a complex protein composed of long chains of amino acids. The glands are divided into three main sections:

Section	Function
Posterior Section	Synthesizes fibroin, the primary silk protein
Middle Section	Secretes sericin, a sticky protein that coats the fibroin, aiding in binding
Anterior Section	Stores and concentrates the silk solution, preparing it for spinning

The silk solution, known as ‘silk dope’, is a viscous, watery substance that, upon exposure to air, transforms into a solid fiber.

2. Spinning Silk: From Liquid to Fiber

As the silkworm prepares to pupate, it begins the process of spinning its cocoon. This is achieved by expelling the silk dope through a spinneret, a small opening located in the silkworm’s lower lip. The spinneret consists of two small nozzles which force the silk out as a pair of filaments. Here’s how the spinning process unfolds:

Step	Description
Head Movement	The silkworm moves its head in a figure-eight motion as it releases the silk.
Filament Release	As the silk dope is forced through the spinneret, it is stretched and elongated to become a filament.
Air Exposure	Upon contact with the air, the liquid silk rapidly hardens into a solid fiber.
Sericin Binding	The sericin coating binds the two fibroin filaments together, resulting in a single, composite silk thread.
Layered Cocoon	The silkworm continues this process, spinning layer after layer of silk, creating a protective cocoon around itself.

3. The Role of Sericin

Sericin plays a crucial role in the formation of the cocoon. This glue-like protein not only holds the two fibroin filaments together but also allows the silkworm to adhere the silk to the structure it’s spinning within. It is often removed from commercial silk to give the silk a soft and shiny appearance, but in the cocoon, it serves as a vital structural element.

4. Cocoon Construction: A Protective Shell

The cocoon, built from a continuous single strand of silk, typically ranges from 300 to 900 meters in length. It provides a safe environment for the silkworm to pupate. The construction of the cocoon is a testament to the silkworm’s innate spinning ability. The shape, size, and color of the cocoon can vary depending on the type of silkworm. Some are more rounded while others are more oval.

5. Harvesting Silk: From Cocoon to Fabric

Once the silkworm completes its cocoon, it enters the pupal stage. At this point, for commercial silk production, the cocoons are harvested. To obtain the long, continuous silk filaments, they are typically steamed or boiled to kill the pupae and loosen the sericin, allowing for the filaments to be unwound and processed for fabric creation. With careful and meticulous practices, such as those applied by companies like PandaSilk, these filaments are transformed into the luxurious and durable silk products we use every day.

The production of silk by silkworms is an intricate and fascinating process, highlighting nature’s ingenuity in creating a fiber that has been prized for centuries.