Scientists uncover trick to spider’s stealth

You almost never notice a spider descend from the ceiling until it’s right in front of you. Coming down on its silk thread—the dragline—it barely moves or spins. Now, scientists have figured out why. In a study published this month in Applied Physics Letters researchers collected some golden silk orb-weaver spiders (Nephila edulis and N. pilipes, the latter pictured), raised them in the lab, and collected their dragline silk. They used a device that can measure extremely small forces—the torsion pendulum, the same apparatus that Henry Cavendish used to estimate Earth’s mass about 200 years ago—now equipped with image processing capability. All the other fibers they tested—including human hair, metal wires, and carbon fiber—behaved like an elastic material when twisted, just like a rubber band that comes back to its original shape when twisted or stretched. But, the dragline silk underwent permanent molecular deformation upon twisting. This warping rapidly slows down any movements, steadying the spider. The unique arrangement of molecules in dragline silk—rigid structures that help maintain its overall shape, and soft structures that act like a cushion, absorbing any motion—is responsible for this behavior, the authors suspect. The findings could lead to ropes for rescue helicopter ladders or rappelling climbers that don’t throw us into a spin.