Silk

By | October 8, 2018

Question 1 What is meant by sericulture?

Question 2 What are the characteristics of silk fibres obtained from the cocoons of  silk moth?

Question 3  How will you distinguish between natural and artificial silk?

Question 4 What is meant by reeling the silk? How is it done?

Question 5 What is a cocoon? name the fibre of which a cocoon is made?

Question 6 Describe the life history of silk moth?

Question 7 Describe how silk is produced?

Question 8 What causes sorter’s disease?

Question 9 Name the tree whose leaves provide food for the silkworms?

Question 10 What is silk?

Question 11 What are the different varieties of silk?

Silk

Silk is a fine, strong, soft and shining fibre produced by silkworms in making their cocoons.

Silk is a natural fibre which is obtained from an insect (called silk moth). So, silk is an animal fibre. Silk fibre is made of a protein. The soft looking silk yarn is as strong as a comparable thread of steel.

Silk fibres are converted into silk yarn which is used for making silk cloth. 

The rearing of silkworms for obtaining silk is called Sericulture.

Life History of Silk Moth

life history of silk moth

Silk moth is a kind of insect. The silk moth passes through a worm-like stage called ‘larva’ or caterpillar’ (which is also called silkworm) and an encased form called pupa’ during its development between the hatching of egg and formation of adult silk moth.

This can be written as:

Egg——> Larva(caterpillar) ——> Pupa ——> Silk moth

The larva (or caterpillar) and pupa stages in the life history of a silk moth are totally different in appearance from the adult silk moth. It is the larva (or caterpillar) of a silk moth which produces silk and not the adult silk moth.

The larva (or caterpillar) of a silk moth which produces silk is called silkworm.

(1) The female silk moth lays eggs on the leaves of a tree (such as mulberry tree)

(2) The eggs hatch to form worm-like larvae. The larvae of silk moth are called caterpillars or silkworms. The silkworms feed on the leaves of mulberry tree and grow bigger in size. Silk is formed in liquid form in the two glands in the silkworms’s head.

(3) When the silkworm (or caterpillar) is ready to enter the next stage of its development called pupa, it first weaves a net to hold itself. Then it swings its head from side to side in the form of figure of eight. During these movements of head, the silkworm secretes silk in liquid form through the tiny opening in its head which solidifies on exposure to air and becomes a silk fibre (or silk thread). Soon the silkworm (or caterpillar) covers itself completely by silk fibres. The silky covering spun by the silkworm (or caterpillar) of silk moth is called cocoon. The cocoon is made by silkworm to protect its development as pupa. Pupa is a stage in the life history of silk moth when the caterpillar (or silkworm) becomes ‘encased’ in a hard shell of silk fibres called cocoon. The silkworm continues to develop in the form of pupa inside the cocoon to form the silk moth.

(4) When the pupa (encased in cocoon) develops fully to form an adult silk moth, then the cocoon splits up and a beautiful silk moth comes out. The adult female silk moth then lays more eggs. In this way, the life history of silk moth is completed.

In order to produce silk, the silkworm developing inside the cocoon (as pupa) is not allowed to mature into an adult silk moth. As soon as the cocoon is formed it is used to obtain silk

fibres and the developing silkworm (as pupa) gets killed. This is because if the silkworm (as pupa) is allowed to mature into a silk moth, then the fully formed silk moth secretes a liquid to dissolve a part of silk of the cocoon to break it so as to come out of it and fly away. This breaking of cocoon causes damage to its silk threads and hence lowers the quality of silk. The cocoons having developing silkworms inside them are used to obtain silk. Some of the silkworms (as pupae) are allowed to live and mature into silk moths so that they can lay eggs to produce more silkworms.

Mulberry is called shehtoot.

Production of Silk

Production of silk

The rearing of silkworms, processing of cocoons to obtain silk fibres and making of silk fabrics (silk cloth) from silk fibres.

(1) Rearing of Silkworms to Obtain Cocoons

A female silk moth lays hundreds of eggs at a time.The eggs of silk moths are stored

carefully on paper strips (or cloth strips) and sold to silkworm farmers. The farmers keep these eggs at suitable temperature and humidity under hygienic conditions. The eggs are then warmed to a suitable temperature for hatching. When the eggs hatch, silkworms (larvae or caterpillars) come out of eggs.

The silkworms are fed cut-up mulberry leaves. The silkworms eat day and night and grow

big in size. After about 25 to 30 days, the silkworms stop eating and get ready to spin cocoons.The silkworms climb the twigs placed near them and spin cocoons of silk fibres. The silkworms enclose themselves completely inside the silken cocoons in two or three days.

(2) Processing of Cocoons to Obtain Silk Fibres

All the cocoons are collected at one place. The pile of cocoons is used for obtaining silk fibres. The pile of cocoons is placed in hot water. Hot water makes the silk fibres of cocoons to separate out. The long silk fibres are obtained by unwinding the threads from cocoons. The process of taking out silk fibres from the cocoons for use as silk is called reeling. Reeling is done in special machines which unwind the fibres of silk from cocoons.

(3) Converting Silk Fibres into Silk Cloth

Silk fibres obtained from cocoons are spun (twisted) to form silk threads called silk yarn.

The silk yarn is then woven on looms into silk cloth by the weavers.

Different Varieties of Silk

The silk produced by the silkworms of different varieties of silk moths is different in texture (coarse, smooth, shiny, etc.). Some of the varieties of silk are : Mulberry silk; Tassar silk ; Mooga silk ; Kosa silk; and Eri silk. These silks are obtained from cocoons spun by the silkworms of different types of silk moths. The most common silk moth is the mulberry silk moth. The silk obtained from the cocoons of mulberry silk moth is called mulberry silk. Mulberry silk is soft, lustrous (shiny) and elastic, and can be dyed in beautiful colours Thus

the most common variety of silk is mulberry silk.

Natural Silk and Artificial Silk

Natural silk is obtained from the cocoons of silkworms and it is made of a ‘protein’. Natural silk is an animal fibre.

Artificial silk (called rayon) is obtained from wood pulp and it is made of modified plant material ‘cellulose. (Paper is also made of cellulose obtained from wood pulp).

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