Revisiting the clap-and-fling mechanism in small wasp Encarsia formosa using quantitative measurements of the wing motion

The ideal clap-and-fling mechanism is described as: clap, the leading edges of the wings touch and then the wings rotate around the leading edge, closing the gap between the wings and producing a vertical force; fling, the wings rotate around the trailing edge or “fling open,” generating a vertical force (the drag required to clap or fling the wings can be 6–10 times larger than the vertical force). Here, we revisit the mechanism from the perspective of wing motion and force production, based on our measured quantitative data and flow computations, and suggest certain modifications to its description: In the clap, the wings rotate to a large angle of attack before they are close to each other and they move close to each other with the wing surface almost vertical, and then they move vertically upwards; i.e., the ideal clap motion is far from the real one. The fling is like the ideal one, except that there is a separation (approximately 0.2 chord length) between the wings. During the clap, there is no large vertical force like that in the ideal clap; however, the clapped wings can reduce the downward frictional drag in their upward motion. During the fling, a large vertical force is produced, like that in the ideal fling, but the drag required to fling the wings is no longer 6–10 times larger than the vertical force and it is even a little smaller than the vertical force.