Silk - the fascination, the concerns, and the solutions
Row of silkworm cocoons on a woven surface, Laos. Image credit: We Animals Media
While silk comes from a variety of anthropods, the vast majority of silk is cultivated from the silk moth Bombyx Mori. These moths are quite dependent on humans, having lost their ability to use their wings through thousands of years of domestication. They are descendants of the wild silk moth Bombyx Mandarina. Silk production traditionally occurs in China (where sericulture originated), India, Korea, and Japan, with China and India accounting for 95% of the world’s silk production (Padaki et. al., 2015). It is a popular choice of textile for a luxurious feel and look in clothing. For example, it is what sarees are typically made of.
Silk is often acclaimed for being a natural fiber. However, like many textiles there are some environmental and ethical concerns. According to the Higgs Index, silk rates very poorly for environmental impact, especially when it comes to energy and water use. In fact, silk appears to be one of the worst textiles according to the index. The Higgs Index has been found to use a superior data collection method compared to disagreeing reports and uses system of checks and balances to remain objective (Wicker, 2020). There is also the concern of toxic chemicals that can be used to prevent disease in the silk worms, metallic salts sometimes used to add luster and can leach into waterways, and hormones sometimes used to boost the growth of the silk worms (Wicker, 2020). As with any fabrics, the dying process can also compromise sustainability.
Silk worms of course turn into silk moths. It takes about two to three weeks for metamorphosis to occur in the cocoon. The cost of reeling silk is 90% depending on the quality of the cocoon (Biswas & Ghosh, 2011). This is why the quality of the cocoon is so important to maximize profits. It is also why silk worms are not allowed to transform into silk moths and emerge from the cocoon naturally, since the hole they leave reduces the cocoon to 80% of its value (Kusama, 2015). Depending on the estimates used, we are killing between 139 billion (139,706,450,400) to 2 trillion (2,391,686,944,000) silk worms per year, usually by boiling or burning them alive (Barwick, 2015).
It is this magnitude of raising a species specifically to cull them that has given some conscious problem-solvers the idea to create ahimsa silk. Ahimsa silk or peace silk is more expensive to produce since it allows each moth to emerge naturally before using their cocoon. To give an idea of the difference in price, a regular silk saree sells for approximately 2000 rupees while an ahimsa silk saree can cost double (Kusama, 2015). There are still concerns from some about this method. One concern is if it is moral to create billions of living beings who can no longer even use their wings or do much else besides sit in a bowl they are placed in until they die? Since the silk moths do not have moving mouth parts to eat and can only breed and die a few days afterwards, does this justify it all? What about the hundreds of eggs that are laid per moth that might be left to dry, or the caterpillars left to starve (Cook, 2004)? Can we really track what was done with the eggs and caterpillars when we buy an ahimsa silk clothing piece? Are we really getting a clothing piece made from a wild caught cocoon which only accounts for a tiny fraction of ahimsa silk (Cook, 2004), which is already a fraction of the overall market?
The topic of silk can test your moral compass. Some will admit that they simply do not care about producing silk worms only to kill them in their cocoon. While this statement may be offensive to some, it is a truthful claim from the speaker who may or may not be informed of the magnitude of cruelty. Others may try to convince with the oxymoron that they are animal lovers but are somehow simultaneously happy to wear silk which comes from killing another species. Another point given is placing the concern for plastic pollution above the lives of animals. Plastic pollution is of course an important concern, but may come across as a more truthful argument when one does not regularly consume fish - of which comes from the industry accounting for the vast majority of plastic in the oceans. Regardless of how it is rationalized, it is clear that people do not want to sacrifice the beauty of silk.
Silk also has peculiar strength qualities. Especially spider silk, which is twice as strong. It is even several times stronger than steel and comparable in strength to kavlar. Spiders cannot be placed together in large groups for mass production due to their territorial and cannibalistic tendencies. Instead, scientists tried other methods to grow large quantities of spider silk. One method included placing spider DNA in goats, with the goats producing the spider silk in their milk. This method was first engineered by a Montreal-based biotechnology company in at the turn of the millennium (Zehr, 2000). More commonly, spider DNA is placed in silk worms which then produce the silk in the traditional way. The spider silk fabric, dragon silk, is a mesh bulletproof material already used for bulletproof vests in the US army (Burton, 2020). While harnessing the properties of spider silk in this way may seem fascinating, it still leave us with the same production concerns as traditional silk production.
Fortunately, the future is bright for combining the beauty and strength of silk with conscious choices that respect nature. Instead of exploiting nature – which of course is notorious for detrimental consequences – we can learn from nature and make our own spider silk without animals and athropods using modern technology. Bolt Threads is a leader in creating such high-performance materials. They are replicating spider silk to make their material, Microsilk, which can be produced with a lower environmental impact than traditional textile production and can be biodegradable (Bolt Threads, 2020). The company shows images of dresses made in collaboration with Stella McCartney on their website.
Plant-based alternatives include lotus silk and Orange Fiber.
References
Barwick, M. (2015, May 13). “Is silk vegan? How is it made?”. Bite Sized Vegan. Retrieved August 4, 2020 from http://www.bitesizevegan.org/bite-size-vegan-nuggets/qa/is-silk-vegan-cruel/
Biswas, A. and Ghosh, A. (2011). “Silk cocoon grading by fuzzy expert systems”. Soft Computing in Textile Engineering. p 384-402. DOI 10.1533/9780857090812.5.384
Bolt Threads (2020). Meet Microsilk. Bolt Threads. Retrieved August 4, 2020 from https://boltthreads.com/technology/microsilk
Burton, S. (2020). “Spider silk is now being used to make armor”. Body Armor News. Retrieved August 4, 2020 from https://www.bodyarmornews.com/spider-silk-is-now-being-used-to-make-body-armor/
Cook, M. (2004). “Ahimsa (peace silk)”. Worm Spit. Retrieved August 4, 2020 from http://www.wormspit.com/peacesilk.htm. See also http://www.wormspit.com/bombyxsilkworms.htm
Kusama, R. (2015, March 24). “Kusuma Rajaiah's ahimsa silk documentary by Goethe Zentrum - Part1”. https://www.youtube.com/watch?v=cp7MlAtNiVs
Padaki, N.V., Das, B., and Basu, A. (2015). “Advances in understanding the properties of silk”. Advances in Silk Science and Technology. p 3-16. DOI 10.1016/B978-1-78242-311-9.00001-X
Wicker, A. (2020, March 4). “Why does silk have such a bad rap?”. Ecocult. Retireved August 4, 2020 from https://ecocult.com/why-does-silk-have-such-a-bad-environmental-rap/
Zehr, L. (2000, January 13). “Nexia's transgenic 'spider goat' to produce milk of steel”. The Globe and Mail. https://www.theglobeandmail.com/report-on-business/nexias-transgenic-spider-goat-to-produce-milk-of-steel/article1035969/