Silkworms and us

2008-09-18 00:00

Following the craze for water crystals or “squidgies”, another craze is in full swing: keeping silkworms. Parents (like me) who were recently sharing tips on where to buy squidgies are now trading information on where to find mulberry leaves.

A spokesman for Howick Prep School said many children had silkworms at home but had not yet brought them to school. “Some classes have started to study themes related to nature, so we will encourage pupils in those classes to bring their silkworms to school,” she said.

Sally Kelly, a Grade 1 teacher at Laddsworth Primary in Hilton said the worms are not as common as in previous years, but some pupils have brought them to school.

Lee Perrett, a Grade R teacher at Hilton Pre-Primary, keeps some in her classroom. She said they did not seem to be as popular as in previous years and suggested that perhaps squidgies had met children’s need to have some kind of pet to nurture. “The silkworms have been a wonderful learning and teaching tool because they have generated discussions about all kinds of related topics, not just their life cycle.”

She advised parents to make sure that their children’s worms are in a box with tall sides once the worms get big enough to spin their cocoons, as they like to attach themselves to vertical surfaces. “After that, keep the lid on the box as although the moths cannot fly, they can crawl out once they emerge from their cocoons.” She suggested parents keep only a small section of cardboard with eggs on it, otherwise “you find yourself with literally hundreds of worms when they hatch again next season.” Unfortunately, getting rid of unwanted eggs means doing something like burning the box or squashing the eggs underfoot.

Silkworms are not worms at all, but the caterpillar or larval stage of the Bombyx mori moth. They are also called silkworm moths or mulberry moths as the larvae’s natural food is mulberry leaves (Morus alba), as generations of harassed parents (like me) know. The original wild ancestor of the cultivated species is believed to be Bombyx mandarina Moore, a silkmoth unique to China that lives on the white mulberry tree. Today, Bombyx mori live only in captivity because the moths lost their sight and the ability to eat or fly when they were domesticated, making it impossible to survive in the wild.

Silkworm larvae hatch from a tiny black egg and spend the next four-to- six weeks eating mulberry leaves almost constantly (ask me, I know) until they are about seven centimetres long. These white caterpillars shed their skin or moult several times during this stage before spinning a white or yellow silk cocoon around themselves, which takes about three days. Inside, the larvae change into hard, brown-shelled pupae. Adult moths emerge in about three weeks to reproduce and die, which takes about five days. The female moths lay between 200 and 500 lemon-yellow eggs that eventually turn black.

The commercial silk industry produces silk fabric from the cocoons that consist of a single continuous thread about 300 to 900 metres long. Cocoons are boiled to kill the pupae inside and help unravel the silk which is then wound onto reels. Between five and eight strands are combined to create one thread. Only a few moths are allowed to emerge and lay eggs to continue the population of silk worms. In China, people eat boiled silkworm pupae.

People have been cultivating silkworms for between 4 000 and 5 000 years. Sericulture or the production of raw silk from silkworms began in China, where they were first domesticated. Sericulture spread to Korea and later to Japan and India. Legend has it that around AD 550 two monks working for Emperor Justinian I stole several silkworm eggs and seeds of the mulberry tree and so sericulture began in Constantinople. Today it is practised in Japan, China, Spain, France and Italy, although artificial fibres have replaced the use of silk in much of the textile industry. Silk is used not only for clothing, but in a wide variety of other applications from medicine to space technology.

juliadd@witness.co.za

For more information visit

• http://www.silk-road.com

• http://www.insected.arizona.edu

• http://www.enchantedlearning.com

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