The silk worm isn't really a worm, but the caterpillar (larva) of a moth, Bombyx mori. The caterpillar spins a cocoon before turning into a moth and it is this cocoon that yields the thread we call silk.
Learning about the metamorphosis of the silk worm and how it is used to make silk textiles, can make a fascinating lesson about the natural world and how it is utilised and shaped by humans.
Over the years, silk worms have been domesticated for silk production to such an extent that the caterpillars have lost their resistance to disease. And adult moths can neither fly nor eat. Also, in commercial silk production, most larvae are killed before they emerge in order to preserve the cocoon. This can raise ethical questions, including with the supposedly "humane" Ahisma method of silk production (which does not rely on killing the larva).
Lifecycle of a silk worm:
1 - 3 weeks: From a tiny egg a small caterpillar hatches.
3 - 4 weeks: The larva grows in four stages, or instars, as it eats mulberry leaves or artificial food and sheds its skin.
2 - 4 days: The caterpillar then spins a cocoon of silk around itself. In silk production, the cocoon is then heated to kill the caterpillar inside and use the cocoon for its silk.
2 - 3 weeks: It turns into a pupa which emerges from the cocoon.
1 - 3 days: The pupa then becomes a non-flying moth, mates and, if female, lays hundreds of eggs. After this the moth will die.
Sericulture is the production of silk, and was long-kept secret by the Chinese, who first began cultivating silk worms and weaving the thread into textiles, around 2700 BC. The practice then finally migrated west, with silk worm eggs thought to have been smuggled out of China by monks. Sericulture then started in India and by the 6th century in and around Constantinople, then in Italy (12th century) and France (16th century) before James I tried to start a silk industry in England in the 17th century.
The process usually involves allowing the silk worms to grow and spin their cocoon, before they are heated in hot water, killing the larva but allowing the silk to be easily reeled from the cocoon.
Growing silk worms
If you would like to rear silk worms, there is a wealth of information online to guide you, with useful links including:
- Silkworm Store - Guide to raising silk worms
- I Like Bugs - Rearing Silkworms at Home
- Worm Spit - A rearing journal
Creating silk textiles
You can create silk letters and shapes without the need to kill the pupa before they hatch, although this is not without its ethical considerations. Below are some of the articles you can find online on using silk: