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draw the diagram of life cycle of a silk moth and explain

Asked by Kevin Kuriakose(student) , on 13/2/13


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Posted by Vaibhav(student)on 13/2/13

The Lifecycle of the silk worm

What is silk?

Silk is the natural fiber produced by silk moths when making a cocoon to go through the metamorphosis of changing from a caterpillar to a moth.  Okay, you 're thinking "silk comes from a worm 's butt??  ... You 'd be wrong!  Silk is made by the silk worm 's spinnerets which are located under the animals mouth.  Make you any less grossed out?

Silk knitting yarn is made from silk cocoons. The type of food fed to domesticated moths determines their silk 's natural color; this can be white, green or yellow.   The Mulberry-feeding moth Bombyz Mori, which is the principal source of silk, is one of the largest and most handsome moths. The male is 1/2 inch in length and the female is a little shorter and stouter. The larva is ashy gray or cream color and about 3 to 3 1/2 inches long. There is a spine-like horn at the tail.

The common silk worm produces only one generation during the year where the seasons are defined. In some areas, such as India and China, reproduction is almost continuous. Its natural food is the foliage of mulberry trees.  The silk glands consist of two long thick-walled sacs running along the sides of the body, which open by a common orifice - the spinneret or seripositor - on the under lip of the larva.

When the larva is fully mature, it proceeds to spin its cocoon, in which it ejects from both glands a continuous and reelable thread of 800 to 1,200 yards in length, moving its head around in regular order continuously for about three days. The filament produced averages 1/1,200 of an inch in thickness. The cocoons average one inch to 1 1/2 inches in length. From ten to twelve days after the completion of the cocoon, the insect is ready to escape. A perfect moth comes forth and the sexes almost immediately couple. In four to six days, the female lays her eggs numbering over five hundred. With their life cycle completed, the moths soon die.

With the exception of those selected for reproduction of eggs, the cocoons are treated to preserve them intact. The chrysalis must be killed without damage to the cocoon. The worm spins the cocoon with one continuous thread forming a figure eight. Cutting the cocoon at one end to allow the moth to escape will cut the continuous thread into thousands of short ones. [excerpts from Encyclopedia Britannica]

Workers remove the boiled cocoons from the vat and find the end of each strand of silk. It is then threaded overhead. A single thread of silk can measure up to 4,000 feet in length.  This process is still done in small cottage industries.  In many production facilities, the larvae is actually eaten!  Depending on the desired thickness of the silk fibers, these single threads of silk will be joined with others from 3 to over 100 threads thick.  From the boiled cocoons, three strands are twisted and wound together on large wooden wheels.  In the next step, these strands are looped  onto wooden pegs at opposite ends a large room. Twenty-five of these strands made from three single fibers are twisted together in a hand operated wooden machine:  This results in a single strand made up of 75 fibers, which is used for weaving. The resulting strength is amazing.  Natural dyes obtained from roots and herbs are gathered by nomads in the countryside while synthetic dyes are purchased.  The silk threads are boiled in huge copper vats during the dyeing process for varying lengths of time, depending on the color desired.

Where does silk come from?

Geographically, Asia is the main producer of silk in the world and produces over 90 % of the total global output. Though there are over 40 countries on the world map of silk, bulk of it is produced in China and India, followed by Japan, Brazil and Korea.  India is the second largest producer of silk with 17550 MT (2001-02) and also the largest consumer of silk in the world. It has a strong tradition and culture bound domestic market of silk. In India, mulberry silk is produced mainly in the states of Karnataka, Andhra Pradesh, Tamil Nadu, Jammu & Kashmir and West Bengal, while the non-mulberry silks are produced in Jharkhand, Chattisgarh, Orissa and north-eastern states.

Are there different types of silk?

There are four major types of silk of commercial importance, obtained from different species of silkworms which in turn feed on a number of food plants. These are:  Mulberry,  Tasar,  Muga,  and Eri.

Except mulberry, other varieties of silks are generally termed as non-mulberry silks. India has the unique distinction of producing all these commercial varieties of silk.

Mulberry :

The bulk of the commercial silk produced in the world comes from this variety and often silk generally refers to mulberry silk. Mulberry silk comes from the silkworm, Bombyx mori L. which solely feeds on the leaves of mulberry plant. These silkworms are completely domesticated and reared indoors. In India, the major mulberry silk producing states are Karnataka, Andhra Pradesh, West Bengal, Tamil Nadu and Jammu & Kashmir which together accounts for 92 % of country 's total mulberry raw silk production

Tasar:

Tasar (Tussah) is copperish colour, coarse silk mainly used for furnishings and interiors. It is less lustrous than mulberry silk, but has its own feel and appeal. Tasar silk is generated by the silkworm, Antheraea mylitta which mainly thrive on the food plants Asan and Arjun. The rearings are conducted in nature on the trees in the open. In India, tasar silk is mainly produced in the states of Jharkhand, Chattisgarh and Orissa, besides Maharashtra, West Bengal and Andhra Pradesh. Tasar culture is the main stay for many a tribal community in India.

Oak Tasar: It is a finer variety of tasar generated by the silkworm, Antheraea proyeli J. in India which feed on natural food plants of oak, found in abundance in the sub-Himalayan belt of India covering the states of Manipur, Himachal Pradesh, Uttar Pradesh, Assam, Meghalaya and Jammu & Kashmir. China is the major producer of oak tasar in the world and this comes from another silkworm which is known as Antheraea pernyi.

Eri  

Also known as Endi or Errandi, Eri is a multivoltine silk spun from open-ended cocoons, unlike other varieties of silk. Eri silk is the product of the domesticated silkworm, Philosamia ricini that feeds mainly on castor leaves. Ericulture is a household activity practiced mainly for protein rich pupae, a delicacy for the tribal. Resultantly, the eri cocoons are open-mouthed and are spun. The silk is used indigenously for preparation of chaddars (wraps) for own use by these tribals. In India, this culture is practiced mainly in the north-eastern states and Assam. It is also found in Bihar, West Bengal and Orissa.  

Muga :

This golden yellow color silk is prerogative  of India and the pride of Assam state. It is obtained from semi-domesticated multivoltine silkworm, Antheraea assamensis. These silkworms feed on the aromatic leaves of Som and Soalu plants and are reared on trees similar to that of tasar.  Muga culture is specific to the state of Assam and an integral part of the tradition and culture of that state.  The muga silk, a high value product, is used in products like saris (sarees), mekhalas, chaddars, etc.

Posted by Deepak Jangra(student)on 14/2/13

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