Weevils Evolved Nut-and-screw Joint

A scanning electron micrograph of the tapering top of a weevil’s leg shows a curved ridge that functions like the thread on a biological screw, another mechanical marvel that evolved long before humans invented it.

Back when hardware meant bony plates and flesh-rending teeth, a living version of the humble screw evolved naturally in, of all places, the leg joints of weevils. The legs of at least 15 kinds of weevils have tapering, threaded, somewhat pointed ends where their legs meet their bodies. As the leg shifts position, the threaded tip tightens or loosens along a ridge on the inside of a rounded hollow structure, researchers in Germany report in the July 1 Science. “This is the first description of a true screw and nut in an organism,” says coauthor Alexander Riedel of the State Museum of Natural History in Karlsruhe, Germany.

The weevil joint “is remarkable from a mechanical and anatomical standpoint,” says Roy Ritzmann, who studies insect locomotion at Case Western Reserve University in Cleveland. “It does confirm my notion that just about anything that is possible, insects will have evolved.”

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