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The Silkworm and the production of silk

Updated on November 20, 2014

Silkworms foraging

Uploaded to Commons by Rocket000
Uploaded to Commons by Rocket000 | Source

Introduction

Have you ever wondered where silk comes from or how it is made?. In my article Mulberry tree { A study of Trees-14} mention was made of the silkworm,which feeds on the foliage of that tree. This insect,or more properly the larvae of the insect Bombyx mori is a primary producer of silk.

The story originates in China and the Chinese were very protective of their 'secret' production of silk. Indeed, the Chinese authorities went as far as stating " Anyone who divulged the secret of the silkworm would be punished by torture and death. However, it was only a matter of time before the secret was smuggled into neighbouring regions and it reached Japan about A.D.300 and to India A.D. 400.

In the 8th century countries such as Spain began producing silk and four hundred years later Italy began production and several towns gave their names to particular types of silk. It was the Japanese who first applied scientific techniques to raising silkworms and they produced some of the worlds finest silk fabrics.Man has tried to produce other cheaper fabrics such as nylon but this much inferior to silk. it may come as a surprise to learn that one filament of silk is stronger than a comparable filament of steel.

The cultivation of silkworms for the purpose of producing silk is called sericulture.

Here we look in some detail at the history of the raising of silkworm {which properly only refers to the caterpillar }, in Britain along with more modern details where required. The life cycle commences,{ in this work}, as the egg., which were bought in order to raise silkworms.

Adult wild silkmoth Bombyx mandarina

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Eggs of Bombyx mori being collected

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Caterpillars soon after hatching

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Adult moth

Only the healthiest moths are selected for use in egg production
Only the healthiest moths are selected for use in egg production | Source

The egg and resulting larva

In former days the eggs in Britain,were sold at Covent Garden market at the cost of ten shillings per ounce, and it was recommended that great care should be given by the purchaser that they were the proper colour,which when good, were of a pale slate or dark lilac colour. Those that were of a pale yellow colour were regarded as being imperfect.

They were preserved in a cool place { that is in a temperature of from ten degrees to twelve degrees C (55-50F }, until wanted for use. It was said that they would retain their vitality for up to a year.

In order to hatch them a temperature of 86 degrees F was required,for which purpose,in most parts of Europe,where the silkworm was cultivated,the rooms used for that purpose were heated by stoves. However, in regions such as the East Indies,in the Islands of France and Bourbon,and in southern parts of the United States, the natural air temperature was found to be sufficient.

The houses in which the insects were kept was built with numerous windows to allow a good flow of air and furnishes with tables of shelves, on which they were kept. The shelves had movable ledges formed one above the other of a height of inch or more on each side, to confine the insects,and several stages of them was formed in order to admit a flow of air on every side.

When the Mulberry tree began to unfold its leaves,it was time to commence hatching the eggs. They were placed on the shelves at a temperature previously mentioned,and when they began to turn white,which was in about a period of ten days, they were covered by sheets of writing paper,turned up at the edges,and pierced full of holes with a large knitting needle or similar object.

On the upper side of the paper was laid some young twigs of Mulberry,which the insects would smell,and crawling through the holes in the paper would begin to eat as soon as they were hatched. As fast as the twigs became covered by the insects, they were carefully taken and removed to another shelf,where they were placed on a whitey-brown,or any absorbent paper,about one to every square inch.

The silkworm changes its skin four times before it spins a cocoon. Its life is thus divided into five stages. During the first it was fed with chopped or young leaves, fresh ones being given as soon as it had eaten what it had before. At this time it frequently appeared sleep, when it was advised " That on no account should it be disturbed".

When the silkworm was in its second stage, it was fed with young entire leaves,or old chopped ones,and a great part of this stage was passed in apparent sleep.During the third stage the silkworms became more lively and vigorous and they would then devour full grown leaves without assistance. In the fourth stage the silkworm changed to a flesh colour and ate greedily.In the fifth stage the silkworm would eat the coarsest leaves,and it would then feed abundantly day and night,and given plenty air and warmth. According to Louden {1844} " each of these stages were preceded by apparent sickness,and want of appetite y the insect,which became torpid before the change of its skin took place"

It was recommended that the litter made by the waste leaves etc, should be removed ,the insect being attracted to one corner by fresh leaves while the other parts were cleaned.

In these more modern times only the healthiest moths are used for breeding. The eggs are categorized, graded and meticulously tested for infection. Unhealthy eggs are burned.

Silkworm in its natural habitat on a Mulberry tree

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Pupa of silkworm

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Restless and ready to spin the cocoon

When the caterpillars ceased to eat and become restless often moving their heads to and fro and looking up,it was a sure indication that they were preparing to make their cocoons. They would by this stage have become transparent of a pearly colour and the green circles around their bodies would have taken on a golden hue.

At this stage twigs of oak,tufts of dandelion, rolled up shavings of wood, cornets of paper,or sprigs of heath or broom was conveniently placed on the shelves, to serve as support for the caterpillar, the tables or shelves ,first being cleaned and all the litter removed. Once this was achieved the caterpillar would start to make its cocoon,with twists of its head it spun a double strand of fibre in a figure of eight pattern and constructs a symmetrical wall all around itself. The filament is secreted from each of the two glands called the spinneret located under the jaws of the silkworm.

The fibre referred to as fibroin makes up 75-90% and sericin, the gum secreted by the caterpillar to glue the fibre to the cocoon,comprises about 10-25% of the silk. Other elements include fats, and salts.

When the caterpillars had done their workings, the cocoons were taken from the twigs and and sorted. Those that were double,or in any way imperfect were thrown aside. A certain number were selected to breed from and the rest were set aside for the reeling of silk. Those that were chosen for the production of silk had to have the larva enclosed destroyed. In nature the pupa would break through the protective cocoon to emerge as a moth. However, sericulturists must destroy the pupa so that it does not destroy or break the precious thread. These days it is achieved by stoving or stifling the pupa with heat.

In days gone by there were several ways of achieving the destruction of the larva. In Italy it was performed by exposing the cocoons to the heat of the sun for three days,from ten am to five pm when the thermometer stood at 88 degrees F. In France they were put into bags or baskets and enclosed for half an hour in ovens heated at 88 degrees F.However,it seems in America , they were generally placed in sieves or boxes having perforated bottoms.They were then covered very closely with a wooden cloth,and placed over steam wither from boiling water or boiling whiskeys or rum.

The larvae being killed and the cocoons cleared of external floss,they were thrown by handfuls into basins of pure soft water,placed over small furnaces of charcoal fires. When the water was almost boiling ,the cocoons were sunk with a whick of broom or peeled birch under water for about two to three minutes,to soften the gum and to loosen the fibre. This however, was deemed unnecessary when they had been killed by steam, of boiling spirits,the gum being disolved by the spirits. The whisk was then lightly moved around until the filaments adhered to it and were then drawn off. As soon as sufficient numbers were collected the 'reeling' began.

Cocoon of the silkworm

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More historical information

The process described above was an insight into the production of silk in days gone by. The following information and advise was given. If well fed, in proper temperatures ,the caterpillars will have finished their labours in 24 days from the period of being hatched and the quantity of silk produced would, other circumstances being equal, be in proportion to the quantity of food devoured. Its quality was dependant on the climate and the soil in which the leaves had been grown.

It was estimated that an ounce of eggs would produce around 40,000 caterpillars,which would consume 1,073 lbs of leaves and produce 80 lbs of cocoons or about 8 lbs of raw silk. However, the silkworms were subject to numerous diseases, the most fatal of which was vulgarly termed the 'tripes',and was brought on by wet or improper food. When they appeared to be sick they would immediately be removed from the rest,as all their diseases appeared to be contagious. It was therefore recommended that wet leaves were never given to silkworms,as they were thought to occasion disease.

It thought better to let the silkworms fast for twenty four hours or even longer,than to give them leaves that were not pee trrey dry. In wet weather, the branches of the tree was gathered and hung up in a dry place or spread out to dry.

It is also on record that in 1792, a Miss Croft of York {Yorkshire England} sent a specimen of silk, of her own raising, to the Society of Arts, the worms produced had been entirely fed on lettuce leaves.

The Modern day process of filature.

The filature is the place in which the cocoons are are processed into silk thread. The cocoons are sorted out by various characteristics which include colour and size in order to obtain a uniform quality. The coccons had been soaked in water to loosen the sericin { viscid substance}. Although the silk is about 20% sericin,only about 1% is removed at this stage. This way the gum is thought to facilitate the following stage in which the filaments are combined to form silk threads or yarn.

Silk reeling

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Reeling of the thread

Reeling may be achieved manually as was the case in former times or automatically. The cocoon is brushed to locate the end of the fibre which is then thread through a porcelain eyelet,and the fibre is reeled onto a wheel. As this process is occurring trained operators check for flaws in the filaments as they are being reeled.

As each filament is nearly completed,a new fibre is twisted onto it,thus forming one long continuous thread. The sericin contributes to the adhesion of the fibres to each other. The end product ,the raw silk filaments are then reeled onto 'skeins'.These skeins are packaged into bundles weighing ten pounds {2.4 kg} referred to as books. The books are then further packaged into bales of 133 lbs {60kg} and transported to a manufacturing centre.

The silk threads are twisted together to make certain patterns . The silk is then put through rollers to make it more uniform. After a final inspection it is shipped off to the fabric manufactures.

World silk production has almost doubled over the last half century. China and Japan have been the main producers with India having now a significant share of the market,together manufacturing over 50% of the worlds production.

Footnote. The domesticated silk moth Bombyx mori was thought to have been bred from the wild silk moth Bombyx mandarina which occurs in China, Japan and Korea.

Did you know that the wedding dress of the current Queen of England was made from silk.?

Courtesy of Vintage Fashions,taken from British Pathe. Standard You Tube License

Comments

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    • D.A.L. profile imageAUTHOR

      Dave 

      3 years ago from Lancashire north west England

      aviannovice ,

      Hi Deb,glad to have shared this with you. Nature is a wonderful thing indeed. Best wishes to you.

    • aviannovice profile image

      Deb Hirt 

      3 years ago from Stillwater, OK

      Fascinating reading. I never knew about the process for silk until now.

    • D.A.L. profile imageAUTHOR

      Dave 

      3 years ago from Lancashire north west England

      tiagodamiao,

      Hi, Thank you for your visit. Glad to have revived some memories for you. Best wishes to you.

      sallybea,

      Glad you enjoyed it and that it Brought back some lovely childhood memories for you. I like the idea of the heart shaped card. Best wishes to you.

      DDE,

      Hello Devika, I like the idea of the Croatian tradition. Thank you once again for your encouraging comments and the votes are much appreciated. Best wishes to you..

    • DDE profile image

      Devika Primić 

      3 years ago from Dubrovnik, Croatia

      Incredible! Traditionally most of Croatian women had carried a cocoon of silk in their bosoms.

      I have learned about this from the villagers. You have created an informative and most interesting hub Voted up, interesting, useful, and beautiful.

    • sallybea profile image

      Sally Gulbrandsen 

      3 years ago from Norfolk

      I loved reading this hub. As children we always had silkworms which we kept in a shoe box. We would feed them on Mulberry or Beetroot leaves - the latter would give us red silk instead of yellow. I loved taking off the fluffy silk from the cocoon, for once removed, you could find one thread which you could unwind in one long single thread until you uncovered the chrysalis inside. We also tried to encourage the silkworms to spin their silk around a piece of card shaped like a heart. Lovely to see these images - they brought back so many of my early childhood memories.

    • tiagodamiao profile image

      Tiago Damião 

      3 years ago from Torres Novas

      When I was a kid I had so many silkworms in so many boxes that I had to put them in the garbage. I know that was a bad action, but I was a kid. But still like these worms so much that even in these days I think of me playing with them and give them food.

      Good hub!

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