Nature is full of marvels of engineering that humans have co-opted for their own mechanical feats. Ball and socket joints let your arm bones rotate at the shoulders and also allow the wheels of your car to be turned through the steering column. But it isn't often that a device engineered by humans is later found to also exist in nature. Researchers now report just such a discovery: the joint of a beetle leg that turns inward and outward like a screw . The legs of the beetle, which belong to a species known as the Papuan weevil, have circular threads covering 410 degrees—more than one full rotation around the leg (right). The inside of the joint has corresponding threads (left). Muscles control how much the leg can turn on the screw threads, the researchers report online today in Science. They suggest that the unique features of the joint, which they've now pinpointed in multiple species of weevil, give the beetle extra flexibility when feeding on twigs and foliage, and extra stability when it's in a resting position. It's much harder, they say, to dislocate a screw than a round-ball-and-socket joint.
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