The Secret’s in the Knots

brown recluse

A series of tiny knots make the silk of a brown recluse spider super strong. (Photo credit: Miles Boyer/Shutterstock)

Though most infamous for its deadly venomous bite, the brown recluse is also known for its unusual silk. Now researchers have discovered the secret behind the construction of this dangerous spider’s unique silk.

This discovery comes from a collaboration between researchers from the College of William & Mary in the United States and scientists from Oxford University in England. The results of their research were published in Materials Horizons, a publication of the Royal Society of Chemistry.

A class of spiders called orb weavers makes the spider webs you are likely the most familiar with seeing. These spiders make the circular, spoked webs that you typically see hanging from window eaves, forgotten corners, and doorways. Brown recluses, however, live close to the ground, where their main prey is ground-dwelling insects. Their webs are much more messy in construction.

Watching the spiders construct their webs for hours on end provided the researchers with the clues they needed to understand why these spiders’ webs were so strong. It turns out that the spiders spin unique micro-loops into each strand of silk. According to the researchers, each spider has a spinneret that functions as a “high-speed sewing machine” that makes micro-loops at a rate of 500 tiny loops per inch.

“The theory of knots adding strength is well proven,” William & Mary Professor Hannes Schniepp said. “But adding loops to synthetic filaments always seems to lead to premature fiber failure. Observation of the recluse spider provided the breakthrough solution; unlike all spiders its silk is not round, but a thin, nano-scale flat ribbon. The ribbon shape adds the flexibility needed to prevent premature failure, so that all the micro-loops can provide additional strength to the strand.”

While each individual loop is quite strong on its own, like any knot, it will eventually unravel. However, the cumulative effect is that all of the loops, when taken together, make the fiber much more resistant to failure.

“It’s one of the best silks among all the thousands of species of spiders,” Schniepp said. “In talking about materials, we use terms like ‘strength’ and ‘toughness.’ And in both categories, recluse silk is an extremely good material. If you normalize strength by weight, it’s better than steel. If you look at the toughness of the material, it’s better than Kevlar.”

The researchers hope to use their discovery to develop a new fiber technology. The scientists think that this new fiber could have wide-ranging applications.

“Computer simulations demonstrate that fibers with many loops would be much, much tougher than those without loops,” Oxford University Professor Fritz Vollrath explained. “This right away suggests possible applications. For example carbon filaments could be looped to make them less brittle, and thus allow their use in novel impact absorbing structures. One example would be spider-like webs of carbon-filaments floating in outer space, to capture the drifting space debris that endangers astronaut lives’ and satellite integrity.”

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