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
