Silk Series: About Silkworms

For the cotton-centered sewist, silk tends to be the most mysterious and daunting of fibers. I’ll try to demystify silk for you in a series of posts this week. Like previous series on rayon and linen, I’ll talk about how the fabric is made, different weaves and knits, and sources for buying yardage.

Today: all about silkworms and the process of silk harvesting.

silkworms

Silkworms, by Fastily on Wikimedia Commons

Morus Alba - White Mulberry Tree

The white mulberry tree, by Luis Fernández García.

The silkworm is the larva (caterpillar) of the moth Bombyx mori, a domesticated moth that no longer occurs in the wild and, in fact, cannot live outside the controlled environment provided by humans. They are descended from Bombyx mandarina, which still exist in the wild. Wild silk is harvested and made into textiles as well. Many sources use the term “tussah” to refer to any wild silk, but it is actually silk from a particular species of moth, Antheraea pernyi. More about tussah here.

Silk Moths - Public Domain Illustration

Silk Moths – public domain illustration from Wikimedia Commons

The female adult lays eggs, which take 10-14 days to hatch. The larvae eat the leaves of the white mulberry tree, a native of China. Over the next two weeks, they eat day in and day out, multiplying in size many times over and molting four times in the process.

Silkworm cocoons

Silk cocoons, from Katpatuka on Wikimedia Commons

The silkworms spin a cocoon from their salivary glands — this is silk in its raw form. The silkworm inside is killed by heating, usually by steaming. If the moth is allowed to hatch, it damages the thread. One cocoon contains 900-1,500 meters (2,900-4,900 feet) of ultrafine raw silk filament. Dipping the cocoons into hot water starts the unraveling process.

cocoonthreads

Unreeling cocoon threads, by by Michael Cook, www.wormspit.com

These filaments are spun together to make silk yarn, which can then be woven or knit to make cloth. It takes at least a couple thousand cocoons to produce one pound of silk.

People for the Ethical Treatment of Animals has a stance against silk. What do you think? Are you upset that insects have been bred so much that they can no longer live apart from humans? About the massive amount of insect death that must occur to harvest the silk?

You might be asking about the environmental impact of silk production. According to author Kate Fletcher in the book Sustainable Fashion and Textiles: Design Journeys, cultivation of the mulberry trees requires far fewer chemical fertilizers and pesticides than conventional cotton, since the worms are very sensitive to these chemicals. Wastewater from degumming the fibers is a minor pollutant. Overall it’s relatively eco-friendly, but that’s not including the dyeing, printing, and post-processing methods that have varying degrees of environmental impact.

Did you know you could grow silk at home (or in the classroom)? Cultivating silkworms for their silk is called sericulture, and there is even a little amateur sericulturalist community on the web. Wormspit.com is is not only just about the best name for a website ever, it shows the process step-by-step with tons of pictures. You can get a good idea of the size of the worms and their cocoons. There’s also an interesting blog. Below, a segment from the HGTV show That’s Clever featuring wormspit.com proprietor Michael Cook harvesting silk and weaving a bookmark from the yarn.

Sources: Silk Road Foundation; Wormspit.com; Wikipedia: silk, silkworms, sericulture; books: All About Silk: A Fabric Dictionary & Swatchbook (Fabric Reference Series, Volume 1) by Julie Parker; Sustainable Fashion and Textiles: Design Journeys by Kate Fletcher.

Big thanks to Michael Cook for helping me correct several errors in the first draft of this post.

18 Comments

  1. Really interesting thanks. I have never seen the cocoons, and have always wondered what they look like.

  2. Cass Ward says:

    I remember when we were kids we used to keep silkworms in a cardboard box and feed them mulberry leaves. You don’t see too many mulberry trees anymore here in Australia

  3. Melanie says:

    A great post, thank you. Like Cass, I also used to keep silkworms when I was about 5 years old. My grandma and my next door neighbour both used to have mulberry trees, so that’s where I’d get their leaves. I used to then get the silk from the coccoons. Not sure what I actually did with the silk after that, but found the whole process fascinating.

  4. Esclarmonde says:

    Great post ! I also kept silkworms in the south of France when I was young. We used to go “harvest” mulberry leaves after school with my dad. I didn’t want to boil the worms then so we ended up with lots of butterflies buzzing around the kitchen !

  5. Sonya says:

    I followed the link from whip up and have just recently been pouring over the wealth of information that is Worm Spit after knitting with a variety of hand reeled silk yarn. Silk is amazing stuff.

  6. Ros says:

    cultivation of the mulberry trees uses far toxic chemicals than cotton

    Far more? Far less?

  7. [...] Up is celebrating silk week – and making me drool at all of the wonderful vintage silk swatches they’ve been show [...]

  8. Fe says:

    Wow, that’s pretty darn amazing. I’ve always wondered how it all happened. Can’t wait to hear more and also see your other series on rayon and linen. Thanks for the info.

  9. Sherezada says:

    Great article. My mother still raises silkworms for her class, so it’s neat to hear about the actual silk production aspect of the process.

  10. madame craft says:

    Awesome video!! very interesting, thanks

  11. Lara says:

    Yup – I’m against unnecessary death :)

    It might be more correct to state that although allowing the moth to hatch damages the thread, Peace Silk comes from hatched cocoons, which explains it’s slubby and slightly rougher texture.

    http://www.aurorasilk.com/info/peacesilk.shtml

    PETA might still be against Peace Silk, but it’s a better alternative for those of us that do use some animal products, but don’t consume products that require somebody (or thousands of somebodies) to die.

  12. Violet Lewis says:

    PETA and I have our differences. I would never willfully kill and animal unless my life or others were in danger. The way they jumps all our President for his puppy was uncalled for. Anyway I love your sight and which I had learned MORE ON WEAVING Years ago. BE WEll

  13. [...] article with several cool pictures about silkworms and how the silk is collected.+ The video is pretty interesting to watch, [...]

  14. Lauren says:

    Woah thanks for the article. What an intricate process. Always been a fan of the texture, but when I learned about the boiling of the worms when I went vegan in 1999, I stopped using it. The death of any living creature bums me out and silk is so easy to avoid. Oddly enough, when I would tell people about my stance, I was often told that the boiling was a myth. 3 cheers for the Interwebs bringing endless info and beautiful photos!
    Thanks Lara for the link to Peace Silk. Never heard of “cruelty free silk”, as it were, but I’m curious and glad to have a website to begin researching with.

  15. [...] True Up, which is a great blog about all things fabric. Just recently, I’ve learned all about silk and gotten a peek in the Quilt Market. True Up also regularly posts about US and international [...]

  16. terisa says:

    I actually raised a batch in college for fun. They are really amazing to watch.

  17. shivam kumar dutta says:

    this is very intresting & i learn many things in this video,i share this video to my fashion designing friends.i really thanks for this video.