Process of rearing silk worm

Animal fibres of Class 7

Steps and Process of rearing silk worm

Silk fibres are also animal fibres. Silkworms spin the ‘silk fibres’. The rearing of silkworms for obtaining silk is called sericulture. Find out from your mother/aunt/grandmother the kind of silk saris they have

Life history of silk moth

The most common and popular among the silk moths is Bombyx mori which is popularly called the mulberry silkworm, as its main feed is mulberry plant.

The entire life history of mulberry silk worm is divided into four stages-

Adult
Egg
Larva
Pupa

Lets discuss all the above four stages in details

Adult stage:

The adult silk moth consist of the following characterist

It is about 2.5 cm length
Pale creamy or some time white in colour
The moths are dioecious (male and female moths are separate).
In the female, (heavy body as compared to male) and generally weak wings flight is impossible.
The female moths are larger than the male.
The moth has got three pairs of legs and there are two pairs of wings. The female moth generally does not feed during its very short life of about 2-3 days.

Fertilization:

Fertilization is takes place after copulation.
After Fertilization female produce egg and it takes about 24 hours to complete the entire process
A single moth can give between 400 to 500 eggs
The number of egg can be higher than this or lower it depends on climatic conditions
All eggs are usually found on the upper surface of the mulberry leaves.
The eggs are present in clusters and are enclosed in a gelatinous substance which is secreted by the female moth.
This gelatinous substance helps eggs for the attachment of the eggs to the leaves.

About Egg

The egg are spherical, small and white in color.
In one gram approximately 1000 eggs present
slowly the colour of egg becomes dark
in mulberry silk worms there are two types of eggs are present (the mulberry silk moth in India can complete five life cycles per year.)

Hatching of eggs:

After 10 days of incubation, the eggs are hatched into larvae called the caterpillar. And this stage is the most critical stage in the life history of the silk moth. The caterpillars are voracious eaters and need a continuous supply of food (mulberry leaves). If the food supply is not sufficient it might possible that the larvae may die.

Caterpillar (larva):

Initialy the lerva is about 1/8th of its original length
Color of its body is yellowish white
In this stage the larvae develops a mouth part
In structure, the The body of larval body is made up of 12 segments and the abdomen of larvae is of 10 segments and has 5 pairs of pseudo-legs.
In the last anal segment there is a small dorsal horn.
The silk worms undergo moulting (ecdysis) four times and the stages in between the mountings are called instars.
There are 5 instars in the larval stage of silk moth.
The first instar larva can feed only on tender leaves of mulberry
The first instar larva grows rapidly.
After the 1st,2nd,3rd and 4th moultings the larva grows into second, third, fourth and fifth instars respectively.
The entire process upto the 5th instar stage takes about 21-25 days after hatching.
The final stage is 5th stage larva or the caterpillar
The caterpillars at the above stage are fully grown and measure about 7.5 cms in length between 4 to 6 gms
The caterpillars develop salivary glands and generally stop feeding before they reached the pupa stage

Pupa:

The fully grown caterpillars stop eating and gradually withdraw towards a comer among the leaves in the feeding trays This is the next stage of development.
Slowly it secrete a sticky fluid through the silk glands. And the fluid comes out through a narrow pore located on the hypopharynx of the caterpillar.
The fluid gradually comes out in the form of delicate threads which hardens on exposure to air.
Gradually the number of threads coming out of the caterpillar increase and they form a covering around the body called the cocoon.

Cocoon:

The color of cocoon is white
It is made up of closed weaving of silk threads
The maximum length of single continuous thread is about 1000-2000 Meters in length
The arrangement of the thread in the cocoon is in a concentric manner.
In order to arrange the thread in a concentric manner the pupa rotates its head at the rate of 65 times per minute constantly
It is estimated that about 2500 cocoons can yield one pound of silk
At the end of this stage the pupa would have grown into an adult (imago) and it comes out of the cocoon by cutting it open.

Emergence of the adult moth (imago):

Metamorphosis is the term used for the pupa when it is inside the cocoon undergoes physiological and morphological changes .In this stage the abdominal pseudo legs disappear and two pairs of wings develop in the same palce. The moth when it is inside the cocoon secretes a basic (alkali) fluid which moistens one corner of the cocoon. At this point, the cocoon is soft and the moth cuts the threads to make a hole. It is through this the adult moth comes out of the cocoon.