Why Spiders Don’t Do the Twist

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An descending spider can avoid uncontrolled swinging that might attract a predator. (Image credit: Anthony Carré)

A new study reveals that dragline silk, the stuff spiders use to rappel, has a molecular structure that makes it resilient to twisting.

Researchers attached a small object that weighed about the same as an Araneau diadematus spider to three types of thread and gave it a spin. They twisted the weight though several 90-degree rotations and recorded how long it took for the thread material to return to its original position.

First up, Kevlar thread. Although this stuff is used in bullet-proof vests, it doesn't make for very good spider silk because it does little to dampen the effects of twisting.

Next, researchers tested soft metallic copper thread. Copper dampened the twisting the best as the rod barely oscillated. But the copper became brittle after just a few twist cycles.

The winner: spider silk.

Silk drawn from an A. diadematus spider did not dampen twisting as well as copper, but it proved highly resilient. Examination at the microscopic scale revealed that dragline silk's molecular configuration gives it shape "memory," which means it totally recovers its initial form and reduces twisting.

This is good news for spiders, since twisting can lead to swinging, not good when you're trying to sneak up on prey or avoid predators.

"A spider should not swing since a (descending) spider is potentially attractive for predators," study coauthor Olivier Emile of the Universite de Rennes in France told LiveScience.

The study is detailed in the March 30 issue of the journal Nature.

Bjorn Carey
Bjorn Carey is the science information officer at Stanford University. He has written and edited for various news outlets, including Live Science's Life's Little Mysteries, Space.com and Popular Science. When it comes to reporting on and explaining wacky science and weird news, Bjorn is your guy. He currently lives in the San Francisco Bay Area with his beautiful son and wife.