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:
- Plenty of mechanisms have been observed in nature before being adopted by engineers. Human hips and shoulders, for instance, are ball-and-socket joints—which can also be found in aquarium tubing and car steering systems.
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