Silkworm

 Silk worm or silk moth, is an insect from the moth family Bombycidae. It is the closest relative of Bombyx mandarina, the wild silk moth. The silkworm is the larva or caterpillar of a silk moth. It is an economically important insect, being a primary producer of silk. A silkworm's preferred food are white mulberry leaves, though they may eat other mulberry species and even the osage orange. Domestic silk moths are closely dependent on humans for reproduction, as a result of millennia of selective breeding. Wild silk moths are different from their domestic cousins as they have not been selectively bred; they are thus not as commercially viable in the production of silk.

1. It is otherwise called “Bombyx” and produces silk, It is reared on mulberry leaves.

2. The body is divisible into head, thorax and abdomen. The abdomen is short and stout.

3. The colour is creamish white, the antennae are short and plumose and mouth parts are of sucking type.

4. The two pairs of wings are always held horizontally when the moths are in resting position.

5. The sexes(male and female) are separate and life history is completed through a larval stage the caterpillar or silk worm and a pupal stage – the chrysalis. The female lays about 400 eggs at a time and dies after laying eggs.

 Life cycle:

Egg:

Egg is the first stage of a silkworm’s life cycle. The female moth lays an egg about the size of an ink dot during summer or the early fall. The egg remains in dormant stage until spring arrives. The warmth of the spring stimulates the egg to hatch. The egg of Bombyx mori is a very small and hard structure; about the size of a pin head and resembling a poppy seed. The egg shell provides a protective covering for embryonic development. When first laid, an egg light yellow. A fertile ovum darkens to a blue-gray within a few days.

 

Larva:

The larva is the vegetative stage where growth takes place. The larva of Bombyx mori, commonly called a silkworm, is host specific to mulberry. During growth, the larva molts 4 times. The period between successive molts is called an instar. The silk worm, upon hatching, is about 1/8th of an inch and extremely hairy.

 

Young silkworms can only feed on tender mulberry leaves. However, during the growth phase they can eat tougher mulberry leaves as well. The larval stage lasts for about 27 days and the silkworm goes through five growth stages called instars, during this time. During the first molting, the silkworm sheds all its hair and gains a smooth skin.

 

Pupa:

As the silkworm prepares to pupate, it spins a protective cocoon. About the size and color of a cotton ball, the cocoon is constructed from one continuous strand of silk, perhaps 1.5 km long (nearly a mile). The silk cocoon serves as protection for the pupa. Cocoons are shades of white, cream and yellow depending on silkworm genetics. After a final molt inside the cocoon, the larva develops into the brown, chitin covered structure called the pupa. Metamorphic changes of the pupa result in an emerging moth

If the silkworms are allowed to mature and break through the cocoon, the silk would be rendered useless for commercial purposes. So the encased insect is plunged into boiling water to kill the inhabitant and dissolve the glue holding the cocoon together. The end of the silk is then located and the cocoon unwound onto a spindle to be made into thread.

Cocoon:

Cocoon is the stage in which the larva spins silk threads around it, to protect itself from its predators. The larva traps itself inside the cocoon in order to pupate. The color of the cocoon varies, depending upon what the silkworm eats. It can range from white to golden yellow. The second molting occurs inside the cocoon, when the larva turns into a brown pupa. It takes about 2-3 weeks for the pupa to metamorphose into an adult moth.

 

Adult:

The adult stage completes the life cycle of Bombyx mori. It is the reproductive stage where adults mate and females lay eggs. Moths are flightless and lack functional mouth parts, so are unable to consume the food/nutrition.

Once the adult moth comes out of its cocoon, its only purpose is to find a member of the opposite sex, and mate. Males are larger than females and more active. They flap their wings rapidly to attract the females. Within 24 hours of mating, the male moth dies, while the female lays abundant eggs, after which it dies as well. There on, a new silkworm life cycle begins.

Features of silk

• Silk is strong and shiny fiber
• Silk fiber has high elasticity
• Silk clothes can be worn on all seasons
• Silk is longest natural fiber
• Silk fiber lasts for long time

Importance and uses of silk

• Silk is used to make clothes and curtains
• Silk is used to make synthetic fiber by mixing it
• Silkworm larva are used as food also
• Cultivation of silk improves economy