Why spider silk is nature’s most elusive textile

By Joshua Spencer

Mention silk and most people think of mulberry silkworms, whose cocoons unravel into fine white strands when washed with soap in warm water. They account for 90% of silk production in the world; most of the rest comes from other types of silkworm. Spider silk makes a minute contribution to the silk industry’s output, because docile silkworms are easier to farm than cannibalistic spiders. But its potential is alluring since this silk is stronger and tougher than any other.

Both its beauty and scarcity explain why spider silk has long appealed to fashionistas. In 1709 François Xavier Bon de Saint Hilaire, a French naturalist, gave Louis XIV a pair of spider-silk gloves. In the late 19th century French missionaries in Madagascar set up a small manufacturing hub producing luxury spider-silk textiles, using the silk of Golden Orb spiders: a set of golden bed hangings made there was included in the Paris Exposition in 1900.

Spider silk has extraordinary material properties. Proportionate to its weight, the silk of a Golden Orb spider is tougher than Kevlar, which is used to make bulletproof vests and ranks among the strongest man-made materials. Yet the silk is also light and remarkably elastic.

These properties arise from the spider’s own requirements. Its web is designed to catch prey: it must be light and thin enough so that it cannot easily be seen, yet sufficiently strong and elastic to snare an incoming target. Its toughness comes from the combination of many long, strong filaments that are locked together at regular intervals by stretchable proteins. Spider-silk proteins are nearly double the size of the average human protein. This gives the textile its strength.

Scientists have struggled to replicate this complex molecular structure and the spider’s eco-friendly production process with synthetic versions. One method has been to genetically engineer other organisms to produce the silk: in the early 2000s a biotech company called Nexia implanted spider-silk DNA into a goat fetus. The firm extracted spider-silk proteins from the offspring’s milk, but did not produce the resulting fibre, called BioSteel, for commercial use. In 2017 researchers at Cambridge University made a synthetic spider silk that was 98% water and 2% silica (a compound of silicon and oxygen). The resulting material imitated most of the natural material’s properties and was completely biodegradable, but wasn’t as strong.

The fashion world is keen to develop a synthetic spider silk that would act as a lightweight, eco-friendly alternative to high-polluting textiles such as nylon. Bolt Threads, a startup that promises “sustainable fashion biometrics and fabrics”, has genetically engineered spider-silk genes into yeast, creating a fabric called Microsilk. But the company has so far sold just 50 limited-edition spider-silk neckties and 100 spider-silk hats. For the moment spider silk remains tangled in a web of secrets.■

IMAGE: Alamy