Silk dressesSilk is a natural protein fiber, some forms of which can be woven
into textiles. The best-known type of silk is obtained from cocoons made by the
larvae of the silkworm Bombyx mori reared in captivity (sericulture). The
shimmering appearance for which silk is prized comes from the fibers' triangular
prism-like structure which allows silk cloth to refract incoming light at
different angles.
"Wild silks" or tussah silks (also spelled "tasar") are produced by caterpillars
other than the mulberry silkworm (Bombyx mori). They are called "wild" as the
silkworms cannot be artificially cultivated like Bombyx mori. A variety of wild
silks have been known and used in China, India, and Europe from early times,
although the scale of production has always been far smaller than that of
cultivated silks. Aside from differences in colors and textures, they all differ
in one major aspect from the domesticated varieties: the cocoons that are
gathered in the wild have usually already been damaged by the emerging moth
before the cocoons are gathered, and thus the single thread that makes up the
cocoon has been torn into shorter lengths. Commercially reared silkworm pupae
are killed before the adult moths emerge by dipping them in boiling water or
piercing them with a needle, thus allowing the whole cocoon to be unraveled as
one continuous thread. This allows a much stronger cloth to be woven from the
silk. Wild silks also tend to be more difficult to dye than silk from the
cultivated silkworm.
There is some evidence that small quantities of wild silk were already being
produced in the Mediterranean area and the Middle East by the time the superior,
and stronger, cultivated silk from China began to be imported (Hill 2003,
Appendix C).
Silks are produced by several other insects, but only the silk of moth
caterpillars has been used for textile manufacture. There has been some research
into other silks, which have differences at the molecular level. Silks are
mainly produced by the larvae of insects with complete metamorphosis, but also
by some adult insects such as webspinners. Silk production is especially common
in the Hymenoptera (bees, wasps, and ants), and is sometimes used in nest
construction. Other types of arthropod produce silk, most notably various
arachnids such as spiders (see spider silk).
India and Nepal
Silk, known as Pattu or Reshmi in southern parts of India and Resham in Hindi,
has a long history in India and is widely produced today. Historically silk was
used by the upper classes, while cotton was used by the poorer classes. Today
silk is mainly used in Bhoodhan Pochampally (also known as Silk City),
Kanchipuram, Dharmavaram, Mysore, etc. in South India and Banaras in the North
for manufacturing garments and Sarees. "Murshidabad silk", famous from
historical times, is mainly produced in Malda and Murshidabad district of West
Bengal and woven with hand looms in Birbhum and Murshidabad district. Another
place famous for production of silk is Bhagalpur. The silk from Kanchi is
particularly well-known for its classic designs and enduring quality. The silk
is traditionally hand-woven and hand-dyed and usually also has silver threads
woven into the cloth. Most of this silk is used to make saris. The saris usually
are very expensive and vibrant in color. Garments made from silk form an
integral part of Indian weddings and other celebrations. In the northeastern
state of Assam, three different types of silk are produced, collectively called
Assam silk: Muga, Eri and Pat silk. Muga, the golden silk, and Eri are produced
by silkworms that are native only to Assam. The heritage of silk rearing and
weaving is very old and continues today especially with the production of Muga
and Pat riha and mekhela chador, the three-piece silk saris woven with
traditional motifs. Mysore Silk Sarees, which are known for their soft texture
and expensive class last easily as long as 25 to 30 years, if maintained well.
Cocoon
The tough brown cocoon of an Emperor Gum MothA cocoon is a casing spun of silk
by many moth caterpillars and numerous other holometabolous insect larvae as a
protective covering for the pupa.
Cocoons may be tough or soft, opaque or translucent, solid or meshlike, of
various colors, or composed of multiple layers, depending on the type of insect
larva producing it. Many moth caterpillars shed the larval hairs (setae) and
incorporate them into the cocoon; if these are urticating hairs then the cocoon
is also irritating to the touch. Some larvae attach small twigs, fecal pellets
or pieces of vegetation to the outside of their cocoon in an attempt to disguise
it from predators. Others spin their cocoon in a concealed location - on the
underside of a leaf, in a crevice, down near the base of a tree trunk, suspended
from a twig or concealed in the leaf litter.[3]
Insects that pupate in a cocoon must escape from it, and they do this either by
the pupa cutting its way out, or by secreting fluids that soften the cocoon.
Some cocoons are constructed with built-in lines of weakness along which they
will tear easily from inside, or with exit holes that only allow a one-way
passage out; such features facilitate the escape of the adult insect after it
emerges from the pupal skin.
Silkworm cocoons are processed and used to produce natural silk for clothing.
 An Emperor Gum Moth caterpillar spinning its cocoon.
|  Assortment of Luna moth cocoons.
|  Luna moth emerging from silk cocoon.
| |
 Luna moth pupa removed from cocoon.
|  Pupation of Inachis io
|  Monarch Butterfly chrysalis
|
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