How spiders mastered spin control

Their silk subtly changes shape as it twists, slowing rotation

Nephila edulis spider

STEADY SPIDER  Silk from orb weaver spiders (Nephila edulis shown) deforms when twisted, enabling a steady dangle.

Sam Gordon/Flickr (CC BY-NC-SA 2.0)

A strange property of spider silk helps explain how the arachnids avoid twirling wildly at the end of their ropes.

Researchers from China and England harvested silk from two species of golden orb weaver spiders, Nephila edulis and Nephila pilipes, and tested it with a torsion pendulum. The device has a hanging weight that rotates clockwise or counterclockwise, twisting whatever fiber it hangs from. When a typical fiber is twisted, the weight spins back and forth around an equilibrium point, eventually returning to its original orientation.

But unlike several fibers the scientists tested — copper wires, carbon fibers and even human hair — the spider silk deformed when twisted. That distortion changed the silk’s equilibrium point and cut down on the back-and-forth spinning, the scientists report in the July 3 Applied Physics Letters. Eventually, scientists might design spin-resistant ropes for mountain climbers, who, like spiders, should avoid doing the twist.

SILK STRAND Silk harvested from the golden orb weaver spider Nephila pilipes is shown in a scanning electron microscope image. D. Liu et al/Applied Physics Letters 2017

Physics writer Emily Conover has a Ph.D. in physics from the University of Chicago. She is a two-time winner of the D.C. Science Writers’ Association Newsbrief award.

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