Types of silk

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There are four types of natural silk which are commercially known and produced in the world.  Among them mulberry silk is the most important and contributes as much as 90 per cent of world production, therefore, the term "silk" in general refers to the silk of the mulberry silkworm. Three other commercially important types fall into the category of non-mulberry silks namely: Eri silk; Tasar silk; and Muga silk.  There are also other types of non-mulberry silk, which are mostly wild and exploited in Africa and Asia, are Anaphe silk, Fagara silk, Coan silk, Mussel silk and Spider silk.

Mulberry silk

Bulk of the commercial silk produced in the world comes from this variety and often 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.  Mulberry silk contributes to around 90 percent of the world silk production.

Non-Mulberry Silk

Tasar silk

The tasar silkworms belong to the genus Antheraea and they are all wild silkworms. There are many varieties such as the Chinese tasar silkworm Antherae pernyi Guerin which produces the largest quantity of non-mulberry silk in the world, the Indian tasar silkworm Antheraea mylitte Dury, next in importance, and the Japanese tasar silkworm Antheraea yamamai Querin which is peculiar to Japan and produces green silk thread.
The Chinese and Japanese tasar worms feed on oak leaves and other allied species. The Indian tasar worms feeds on leaves of Terminalia and several other minor host plants.  The worms are either uni- or bivoltine and their cocoons like the mulberry silkworm cocoons can be reeled into raw silk.

Eri silk

These belong to either of two species namely Samia ricini and Philosamia ricini.  P.ricini (also called as castor silkworm) is a domesticated one reared on castor oil plant leaves to produce a white or brick-red silk popularly known as Eri silk.
Since the filament of the cocoons spun by these worms is neither continuous nor uniform in thickness, the cocoons cannot be reeled and, therefore, the moths are allowed to emerge and the pierced cocoons are used for spinning to produce the Eri silk yarn.

Muga silk

The muga silkworms (Antheraea assamensis) also belong to the same genus as tasar worms, but produce an unusual golden-yellow silk thread which is very attractive and strong.  These are found only in the state of Assam, India and feed on Persea bombycina and Litsaea monopetala leaves and those of other species.
The quantity of muga silk produced is quite small and is mostly used for the making of traditional dresses in the State of Assam (India) itself.

Anaphe silk

This silk of southern and central Africa is produced by silkworms of the genus Anaphe: A. moloneyi Druce, A. panda Boisduval, A. reticulate Walker, A. ambrizia Butler, A. carteri Walsingham, A. venata Butler and A. infracta Walsingham.  They spin cocoons in communes, all enclosed by a thin layer of silk.
The tribal people collect them from the forest and spin the fluff into a raw silk that is soft and fairly lustrous.  The silk obtained from A. infracta is known locally as "book", and those from A. moleneyi as "Trisnian-tsamia" and "koko" (Tt).  The fabric is elastic and stronger than that of mulberry silk.  Anaphe silk is used, for example, in velvet and plush.

Fagara silk

Fagara silk is obtained from the giant silk moth Attacus atlas L. and a few other related species or races inhabiting the Indo-Australian bio-geographic region, China and Sudan.  They spin light-brown cocoons nearly 6 cm long with peduncles of varying lengths (2-10 cm).

Coan silk

The larvae of Pachypasa atus D., from the Mediterranean bio-geographic region (southern Italy, Greece, Romania, Turkey, etc.), feed primarily on trees such as pine, ash cypress, juniper and oak.

They spin white cocoons measuring about 8.9 cm x 7.6 cm. In ancient times, this silk was used to make the crimson-dyed apparel worn by the dignitaries of Rome; however, commercial production came to an end long ago because of the limited output and the emergence of superior varieties of silk.


Mussel silk

Whereas the non-mulberry silks previously described are of insect origin, mussel silk is obtained from a bivalve, Pinna squamosa, found in the shallow waters along the Italina and Dalmatian shores of the Adriatic.

The strong brown filament, or byssus, is secreted by the mussel to anchor it to a rock or other surface.  The byssus is combed and then spun into a silk popularly known as “fish wool”.  Its production is largely confined to Taranto, Italy.


Spider silk

Spider silk – another non-insect variety – is soft and fine, but also strong and elastic. The commercial production of this silk comes from certain Madagascan species, including Nephila madagascarensis, Miranda aurentia and Epeira.  As the spinning tubes (spinne-rules) are in the fourth and fifth abdominal segments, about a dozen individuals are confined by their abdominal part to a frame from which the accumulated fibre is reeled out four or five times a month.  Because of the high cost of production, spider silk is not used in the textile industry; however, durability and resistance to extreme temperature and humidity make it indispensable for cross hairs in optical instruments.