Planet Earth

Zooming in on Beetles' Knees, Biologists Find Tiny Screws and Nuts

80beatsBy Valerie RossJun 30, 2011 8:31 PM

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Scanning electron micrograph images of the nut (A,B) and screw (C, D) in the leg joint of a Papuan weevil

What's the News: Biologists spend lots of time poring over nature's nuts and bolts. Now, for the first time, they've found a biological screw and nut---previously thought to be an exclusively human invention. The legs of beetles called Papuan weevils, researchers report

today in Science, have a joint that screws together much like something you'd find in the hardware store. How the Heck:

  • The researchers took x-ray microtomography scans of museum specimens of the beetle.

  • One part of the joint (called the coxa) resembled a nut, with a thread along its inner surface covering 345°. The other part (the trocanter) resembled a screw, with an external thread spiraling around it for 410°---more than a full turn.

  • The beetles' muscles pull on the leg to turn the screw. The beetles don't turn their legs a full 345°, however; they can rotate their front legs by 90°, and their hind legs by 130°.

  • When the scientists expanded their search, they found the same mechanism in the legs of several other species. "The screw-and-nut system appears to be widespread among weevils," they wrote, "and may indeed represent a basic character of the family."

  • These joints may provide additional flexibility, useful to the beetles as they feed on leaves and twigs, as well as help them keep steady when at rest.

What's the Context:

Reference: Thomas van de Kamp, Patrik Vagovič, Tilo Baumbach, & Alexander Riedel. "A Biological Screw in a Beetle’s Leg." Science, June 30, 2011. DOI: 10.1126/science.1204245

Image: van de Kamp et al., Science

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