WEEVIL legs are all screwy. They have the only known built-in screw-and-nut mechanism in the natural world.
While studying CT scans of Trigonopterus oblongus, Alexander Riedel of the State Museum of Natural History in Karlsruhe, Germany, discovered that its legs appeared to be screwed into its body.
The top segment of each leg, the trochanter (centre of the picture), attaches to the insect's body by screwing into a part called the coxa (top left, not to scale), which is similar to a hip.
The screw-and-nut mechanism performs the same function as ball-and-socket joints in vertebrates and hinge joints in other insects. Muscles pull along the length of each leg to draw it into the screw mechanism and make it twist (Science, DOI: 10.1126/science.1204245).
This might be particularly handy for weevils like T. oblongus, which ...