How A Silkworm Makes Silk

by Elizabeth / Thursday, 13 April 2023 / Published in Sericulture

The production of silk by silkworms is a fascinating natural process that has captivated humans for millennia, resulting in the luxurious fabric we cherish. This article delves into the intricate steps involved in a silkworm’s transformation of mulberry leaves into silk threads.

1. The Silkworm’s Life Cycle

The journey of silk production begins with the silkworm’s life cycle. The most commonly used silkworm is the Bombyx mori, which is entirely dependent on human cultivation. Its life cycle consists of four stages: egg, larva (silkworm), pupa, and moth. The silk production occurs during the larval stage.

Stage	Description	Duration	Key Feature
Egg	Tiny, about 1mm, laid by the female moth, often in large numbers	Approximately 10 days, depends on conditions	Dormant stage, needs specific temperature for hatching
Larva	Commonly called a silkworm, it feeds voraciously on mulberry leaves. Undergoes several molts (shedding of skin)	25-35 days	Silk production and rapid growth
Pupa	The larva forms a cocoon around itself and transforms into a pupa. This takes place inside the silk cocoon.	2-3 weeks	Transformation into a moth.
Moth	Emerges from the cocoon. Adult moths do not eat; their sole purpose is to mate and lay eggs.	5-10 days	Reproduction; marks the end of one life cycle.

2. Feeding and Growth

The larval stage is the crucial period for silk production. Silkworms are voracious eaters, consuming large quantities of mulberry leaves. They undergo several molts, where they shed their skin as they grow. During this time, their bodies develop specialized glands that will produce silk fibroin, the protein that makes up silk.

Stage during Larva	Description	Molts	Characteristics
1st Instar	Newly hatched larvae, very small	1st molt	Feeds and grows rapidly
2nd Instar	Slightly larger larvae	2nd molt	Continues eating mulberry
3rd Instar	Noticeably larger, increasing weight	3rd molt	Greater appetite
4th Instar	Larva grows significantly, near maturity	4th molt	Preparing for silk production
5th Instar	Largest larvae, ready to spin silk		Fullest feeding, ready to spin cocoon

3. Silk Production: The Liquid Gold

Once the silkworm reaches maturity, it stops feeding and begins to spin its cocoon. This is when the magic happens. Inside the silkworm’s body, specialized silk glands produce a liquid protein known as fibroin, alongside sericin, a gummy protein that acts as a glue. This viscous liquid is pushed through tiny openings called spinnerets located on its head.

Step	Description	Materials Involved
Fibroin Production	Silk glands produce liquid fibroin	Silk fibroin
Sericin Production	Glands produce liquid sericin, a sticky substance	Sericin
Spinneret Extrusion	Liquid fibroin and sericin forced out through two spinnerets	Combined fibroin and sericin
Air Contact	As the liquid touches air, the proteins solidify into a solid silk filament	Air, solidifying silk proteins

4. The Spinning of the Cocoon

The silkworm moves its head in a figure-eight motion, wrapping the silk filament around itself, creating its protective cocoon. This process takes several days, during which the silkworm continuously spins the silk, layer upon layer, until a complete cocoon is formed. The silk filament is extremely fine, measuring only about 10-25 micrometers in diameter. One cocoon consists of a single silk filament that can be as long as 1000 meters.

Feature	Description
Motion	Figure-eight pattern of the head
Layers	The cocoon is made up of many layers of silk
Duration	The cocoon spinning can take several days

5. The Final Stages

Once the silkworm completes its cocoon, it transforms into a pupa. If left undisturbed, the pupa will eventually emerge as a moth, breaking the cocoon and making the silk filament unusable for textile production. To harvest the silk, the cocoons are typically steamed or boiled. This kills the pupae and dissolves the sericin, which binds the silk filaments together, allowing the continuous silk thread to be reeled. The raw silk is then spun into yarn or thread ready for weaving.