How is silk made from a cocoon?

Soft, shiny, comfy, and breathable, silk has become a precious and beneficial fabric since it had been first collected many centuries ago. Today the industry is worth around $200 to $500 million every year due to the immense and growing demand for items made from silk. However, while it is worth a lot of money, the most reliable way to get the thread is by killing the being that created them – the silkworms.

Silkworms are caterpillars of the Bombyx Mori moth. When it undergoes its pupating period that lasts 3 to 8 days, it releases a sticky liquid protein called fibroin from its two unique salivary glands. It is then propelled via a spinneret, and the thread solidifies when exposed to air.

The caterpillars then release a bonding material called sericin from two separate glands that keep the two threads together. In the process of making its cocoon, the silkworm will have to rotate in an 8-shape motion nearly 300,000 times and create a filament that can stretch about a kilometer.

Left alone, a moth would hatch out from the cocoon in around 12-16 days. However, this would destroy the silk filament. With that, the cocoon is exposed to hot air or steam or put in boiling water. Both processes, however, result in the death of the silkworm’s pupae.

There were other methods tried to preserve the pupae, such as collecting the filaments as the worms release them. However, it was to no avail as the worms didn’t cooperate and bit the threads off.

Using heat processes has another advantage as it breaks down sericin or the bonding agent, allowing the filament to loosen up and be unwounded easier. There are instances where loosened sericin remains on the fibers, and the by-product is regarded as raw silk.

Once raw silk is collected, its strands are spun together to create a fiber with enough durability for knitting or weaving. Various spinning methods are used, and each results in different kinds of threads. These processes include tram, crepe, and organzine, among others.

It takes around 2500 caterpillar cocoons to get a pound or roughly 450 grams of raw silk. With that, it requires billions of cocoons annually to support the demand for the silk industry. Silkworms are cultivated to produce around an estimate of 10 billion cocoons every year.

Sericulture is the process of cultivation of silkworms. It begins with the female moths laying around 300-400 eggs. The moths then die shortly after laying the eggs. Afterwards, the eggs go under incubation for ten days.

They will then hatch, and the worms would measure around a quarter of an inch. Worms will be provided with mulberry leaves, which they will feast on and allow them to produce high-quality silk. They will continue to eat for the next six weeks and grow around 3 inches in length before spinning its cocoons.

China leads silk production in the world, providing 74% of the supply of raw silk. Producing such amount of silk undoubtedly results in many dead silkworms. Not to worry, though, as they are seasoned, fried, and eaten.

However, given that the nature of silk production results in the death of billions of pupae, many animal activists raised their concerns against the silk industry. With that, scientists are trying to work on reasonable methods that wouldn’t require the killing of the silkworms, that may come into actualization soon.

More Readings:

Bombyx mori (Wikipedia)

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