A Comprehensive Guide to Silk Species: Production, Properties, and Types

Silk, a natural fabric renowned for its luxurious qualities, is produced by various species across the globe. This article presents an in-depth analysis of these silk-producing species, their climatic preferences, dietary habits, geographical distribution, annual production capacity, and the technical differences between the various species.

Species Names

Silk, a natural fabric renowned for its luxurious qualities, is produced by various species across the globe. The most common type of silk is Mulberry silk, produced by the Bombyx Mori silkworms. Other types of silk include Bombyx huttoni, Tussah silk (Antheraea Pernyi), Muga silk (Antheraea Assamensis), Eri silk (Samia Cynthia), Thai silk (Bombyx Mori), Bombyx sinensis, Japanese silk (Bombyx Mori), Bombyx textor, Mussel silk (Mytilus Edulis), and Spider silk (Nephila Clavipes). Additionally, there are other types of non-mulberry silk, which are mostly wild and exploited in Africa and Asia, such as Anaphe silk (Anaphe spp.), Fagara silk (Attacus atlas), Coan silk (Pachypasa atus) & more.

Climatic Conditions

Each silk-producing species thrives in specific climatic conditions. For instance, Bombyx Mori silkworms, responsible for producing Mulberry silk, are predominantly found in China & India and require a temperate climate. Tussah silkworms, on the other hand, are found in India and China and prefer a warmer, tropical climate. Thai silk worms thrive in Thailand’s tropical climate, while Japanese silk worms prefer Japan’s temperate climate.

Preferred Foods

The diet of silk-producing species largely influences the quality of the silk they produce. Bombyx Mori silkworms feed exclusively on mulberry leaves, which contributes to the smooth texture and lustrous sheen of Mulberry silk. Tussah silkworms consume a variety of leaves, giving Tussah silk its distinct golden to dark brown color. Thai and Japanese silkworms also feed on mulberry leaves.

Geographic Distribution

Silk-producing species are distributed across various regions worldwide. China and India are the largest producers of Mulberry silk, while Tussah silk is produced in India and China. Some of the popular regions for silk are

1. China:
   • Hangzhou, Zhejiang Province
   • Suzhou, Jiangsu Province
   • Yibin, Sichuan Province
2. India:
   • Mysore, Karnataka State
   • Ramanagara, Karnataka State
   • Dharmavaram, Andhra Pradesh State
   • Murshidabad, West Bengal State
   • Kanchipuram, Tamil Nadu State
   • Srinagar, Jammu & Kashmir State
3. Italy:
   • Como, Lombardy Region
4. Japan:
   • Kiryu, Gunma Prefecture
   • Ueda, Nagano Prefecture
   • Gifu City, Gifu Prefecture
5. Brazil:
   • Maringá, Paraná State
   • Campinas, São Paulo State
6. Vietnam:
   • Van Phuc, Ha Dong District, Hanoi
7. Thailand:
   • Nakhon Ratchasima (also known as Khorat), Nakhon Ratchasima Province
   • Surin, Surin Province
8. Iran:
   • Rasht, Gilan Province
9. Uzbekistan:
   • Margilan, Fergana Valley

Annual Production Capacity

China leads the world in silk production, with an annual capacity of over 53,000 metric tons. India follows with an annual production capacity of around 30,000 metric tons. Thailand and Japan have smaller production capacities, with Thailand producing around 600 metric tons annually and Japan producing around 2,000 metric tons.

Lifecycle of a Silkworm

The lifecycle of a silkworm is a captivating process that unfolds in stages, each with its unique characteristics and importance in the silk production process. This lifecycle is broadly classified into Univoltine, Bivoltine, and Multivoltine, each referring to the number of life cycles the silkworm undergoes in a year.

Univoltine Silkworms: A Single Life Cycle Per Year

Univoltine silkworms, typically found in colder climates, undergo one complete lifecycle – from egg to larva (caterpillar), to pupa, and finally, adult moth – in a year. This fascinating transformation begins when the female moth lays eggs, which hatch into larvae after about two weeks. These larvae feed on mulberry leaves for around 4-6 weeks, after which they spin cocoons using their salivary glands. Inside the cocoon, the larva transforms into a pupa, and after two weeks, an adult moth emerges, ready to mate and lay eggs, thus completing the cycle. Examples of Univoltine silkworms include Bombyx mandarina and Bombyx textor.

Bivoltine Silkworms: Two Life Cycles Per Year

Bivoltine silkworms, common in warmer climates, have two life cycles per year. The stages of their lifecycle are similar to Univoltine silkworms, but the process is repeated twice in a year. This means that these silkworms can produce silk twice a year, potentially doubling the silk yield compared to Univoltine silkworms. CSR1 and CSR2, developed by the Central Silk Research and Training Institute (CSRTI) in Mysore, India, are examples of Bivoltine silkworms known for their high yield and quality of silk.

Multivoltine Silkworms: Multiple Life Cycles Per Year

Multivoltine silkworms, found in tropical regions, can have more than two life cycles per year. These silkworms are capable of producing silk multiple times per year, making them a valuable asset in the silk industry. The tropical tasar silkworm (Antheraea mylitta), eri silkworm (Samia cynthia ricini), and Bombyx mori are examples of multivoltine species.

The fate of the adult silk moth (butterfly) after emerging from the cocoon varies depending on the type of silkworm and the purpose of its rearing. In commercial silk production, the pupae inside the cocoon are usually killed by heat before the adult moth emerges to prevent it from breaking the silk threads of the cocoon. However, in the case of breeding or for non-commercial purposes, the adult moths are allowed to emerge from the cocoons.

Physical Characteristics of Silk

Some of the Physical characteristics of the different varieties of silk are as follows.

Properties	Mulberry Silk	Eri Silk	Muga Silk	Tasar Silk
Origin	China / India	India	India	India
Cross Section Shape	Triangular	Circular	Triangular	Circular
Uses	Textiles, Cosmetics	Textiles	Textiles	Textiles
Colour	White/ Yellow/ Light Green	White	Golden Yellow	Copperish Yellow
Fibre Length (mm)	900-1300	600-700	500-600	500-600
Density (g/cm³)	1.354	1.312	1.308	1.310
Lustre	High	Moderate	High	Moderate
Tenacity	3.75 g/d – 3.85 g/d	2.3 – 4.0 g/d	3.2 – 4.95 g/d	4.5 g/d
Fibre Fineness (den)	2-3                             Fine	3-4                      Coarse	4-7                          Fine	8-12                   Coarse
Texture	Smooth	Rough	Smooth	Rough
Breaking Extension (%)	19%-24%	29%-34%	34%-35%	31%-35%
Elongation-at- break (%)	19%-24%	29%-34%	34%-35%	31%- 35%
Birefringence Value	0.051	0.040	0.037	0.040

Chemical Characteristics of Silk

Amino acid	Mulberry (bi)	Mulberry (cross)	Tasar	Muga	Eri
Aspartic acid	1.64	1.49	6.12	4.97	3.89
Glutamic acid	1.77	1.53	1.27	1.36	1.31
Serine	10.38	10.85	9.87	9.11	8.89
Glycine	43.45	43.73	27.65	28.41	29.35
Histidine	0.13	0.15	0.78	0.72	0.75
Arginine	1.13	1.16	4.99	4.72	4.12
Threonine	0.92	0.76	0.26	0.21	0.18
Alanine	27.56	28.36	34.12	34.72	36.33
Proline	0.79	0.76	2.21	2.18	2.07
Tyrosine	5.58	5.76	6.82	5.12	5.84
Valine	2.37	2.89	1.72	1.5	1.32
Methionine	0.19	0.11	0.28	0.32	0.34
Cystine	0.13	0.12	0.15	0.12	0.11
Isoleucine	0.75	0.78	0.61	0.51	0.45
Leucine	0.73	0.75	0.78	0.71	0.69
Phenylalanine	0.14	0.18	0.34	0.28	0.23
Tryptophan	0.73	0.75	1.26	2.18	1.68
Lysine	0.23	0.25	0.17	0.24	0.23

In conclusion, the world of silk production is a fascinating realm that intertwines nature, science, and artistry. From the humble beginnings of the silkworm, through its transformation within the cocoon, to the final product of luxurious silk, each stage is a testament to the marvels of nature and human ingenuity. The different types of silk, each with its unique properties and characteristics, are a reflection of the diversity of the silk-producing species and their adaptation to various climates and geographical locations. The global distribution of silk production, with India and China leading the way, underscores the universal appeal and demand for this exquisite fabric. As we continue to explore and innovate, the future of silk production promises to be as vibrant and dynamic as the fabric itself.