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