Figure 10.

Dorsal views of two hoverflies from high-speed video of H3 (a–f) and H5 (g–l). Six stages of the stroke are shown, running from the mid-downstroke to the end of the upstroke. Hoverfly H3 (a–f) shows the alula operating in plane with the rest of the wing, except at supination, when it lags the rest of the wing (c). Hoverfly H5 shows the alula operating in its flipped state, in which it is held at a large angle to the rest of the wing at all stages of the wingbeat (white lettering: a = alula).