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Cruelty-free "Peace silk" from an incredible aquatic insect

By: Leena Thorat, York University

Little do we think of a silkworm’s plight when we wear our favourite silk scarf or shirt. The silkworm invests time and energy in building a protective silky covering around its body (cocoon), only to realise that before turning into a beautiful moth, it is going to be boiled to death! That’s the life of a silkworm (caterpillar). Historically, this method dates back to thousands of years and involves killing of the insect to obtain silk.

Peace or Ahimsa silk

So, can there be a cruelty-free alternative to harvesting silk? The answer is yes! Newer ways are being proposed and tested to obtain silk from cocoons without harming or killing the live animal inside. This silk is known as ‘Ahimsa’ or Peace silk. Ahimsa is a Sanskrit word, meaning ‘non-violence’ and in this context, it implies to silks obtained from animals without causing them any pain unlike violent conventional techniques. However, although it is gaining popularity as a guilt-free alternative, a major proportion of raw silk for biomedical, biotechnological and commercial silk fashion industry comes from traditional killing practices.

Chironomid midge: a unique insect to obtain Peace silk

Compared to the terrestrial silkworm, the chironomid midge, an aquatic insect offers a unique advantage for silk harvestation in a cruelty-free way i.e. without killing or harming it in anyway. Midge worms build housing nests using a sticky fluid produced in their salivary glands which is released from their mouth to glue together the surrounding raw material such as soil or sand particles. Nest-building is a natural behaviour of midge larvae for shelter and protection from predators and harsh environmental conditions. Silkworms spin silk in dry surroundings while midges are underwater silk spinners. Thus, midge silk is bound to tiny soil grains while silkworm silk cocoon is made of nearly pure silk fibres composed of fibroin and sericin proteins. The exact composition of midge silk remains untested to date; however, in the 1970s, chironomid scientists predicted that the silk from midges may contain several types of proteins with distinct features.

In a recent study published by our group, we demonstrated that midge larvae can be gently removed from their nests and the same larva is fit enough to be reused for over 20 rounds of nest building. Despite this remarkable benefit, midges have remained underappreciated study models in silk research. Our work indicated several other interesting facts. We showed that the worms mimic their nest-building behaviour in the laboratory using beach sand as a non-toxic, inexpensive, and easily available raw material. These crawlies can construct their nests in ~2.5 hours, the shortest possible time known for any aquatic silk-spinning insect. The final product is a piece of captivating art with a network of silk fibres prominently seen joining the sand particles. It is intriguing to note their distinct pattern of nest construction that involves different kinds of protein deposits- think of it like building a plastered brick wall, where a defined layer of bricks is coated uniformly with a smooth plastering material!

Using an instrument to measure the amount of force needed to break the silk-woven nests, we established that the water-insoluble midge silk fibres have impressive mechanical strength which explains the remarkable stability they impart to these cylindrical silk cases. To fully appreciate the commercial potential of midge silk, we set out to determine its structural and mechanical properties. To do this we developed a novel and non-violent method for extracting silk from the nests. Our findings provide the first direct evidence that the distinct protein structure present in chironomid silk plays a crucial role in rendering durability to the nests. Such a robust architecture ensures that the housing nests are not damaged even in flowing water bodies and are able to protect the worm from enemies and extreme environments.

Our work has shed light on the comparable merits as well as uniqueness of midge silk, notably its superior fibre fineness among all known insect silks. Midge silk offers endless possibilities from a commercial perspective. As an example, it is possible to tinker with the silk extracted from chironomids and create chemical modifications to generate silk with desired features suitable for specific biotechnological and biomedical applications. Since midge and silkworm silk have comparable properties, blended silk varieties can be developed in the future using industrial-level chemical processing methods. And if you were a silk expert, you would have a hard time telling the two silks apart!

Harnessing the amazing engineering skills of midges

Considering the growing demand for alternative sources of multi-purpose silk materials, we envisage chironomid midge as a promising candidate for the Peace silk industry that encourages silk harvestation from animals using cruelty-free methodologies. Based on the promising data from our foundational research, midges could prove valuable models as a source of novel biopolymer for real-world applications. I am now interested to dig deeper and explore other potential aspects of the silk spinning ability of midges. For instance, by inducing the larvae to ramp up their silk production, I aim to obtain huge yield of silk to generate a commercial-scale source for the manufacture of sustainable and environment-friendly biocomposite materials.

Edited by participants of the 2021 Science Writing Internship program and B.G. Borowiec. Header photo from Unsplash. Additional images by Leena Thorat.

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