The silkworm is the lava or caterpillar of bombyx mori (the silkworm of the mulberry tree). It is entirely dependent on humans for its reproduction and its preferred food is white mulberry leaves.
Eggs take about ten days to hatch and the larvae enclose themselves in a cocoon of raw silk produced from their salivary glands. Each cocoon is made of threads of raw silk which are between 300 and 900 metres long.
Tussah silk is a textured wild silk produced by wild silkworms in the tropical and semi tropical forests in China and India. The cocoons are gathered after the moth emerges and the silk is beige or brownish in tone.
Silks absorbency makes it comfortable to wear in warm weather. Its low conductivity also keeps warm air close to the skin during cold weather. Hence it is often used for clothing such as shirts, ties, blouses, high fashion cloths, lingerie and kimonos.
Silk has an attractive lustre and drape which also makes it suitable for many furnishing and upholstery applications.
The silk worm
The lifecycle begins in spring with the opening of the mulberry tree buds, then depending on the breed, the latitude and environment the process can be repeated several times a year.
The rearing process has various stages:
- Egg incubation needs to be undertaken at 23 or 24 degrees Celsius and lasts 12 to 20 days.
- Once hatched the worm starts to eat mulberry leaves, increasing in size and weight and moulting six times over a 30 day period.
- After this time the silk worm climbs onto the twigs or artificial support, and from a gland known as the extruding duct located below the mouth, releases two single filaments of triangular cross-section which join and solidify and are covered with sticky sericin which forms the silk filament.
- The silkworm starts to build a nest among the twigs, forming a cocoon over three to four days. It does this by accumulating layers of filament in the shape of a figure 8.
- Over the next 10-12 days the silk worm becomes a brown leathery-shelled chrysalis, then finally a pupae and finally a moth.
- If the silk cycle is not interrupted by steaming, the moth secretes a highly alkaline liquid which allows it to pierce the cocoon, fly out, mate and lay its eggs and restart the lifecycle after only two days.