Fig. 4. Free-flight smoke visualization of the flow around the wings of Sympetrum sanguineum. There is a leading edge vortex (yellow arrows) on the fore-wing counterstroking flight. (A–H) Consecutive images from a 250 Hz high-speed video recording. Perpendicular views from the b and c cameras show that the dragonfly has taken off and cleared the perch and is holding station, flying sideways in (A) as the forewing completes the upstroke. The downstroke begins in (B), and the LEV is already present when the wing cuts the smoke in (C). The structure of the LEV is consistent as the intersection of the smoke and the wing moves towards the midline (D,E), and the internal flows within the LEV are clear in (F). The LEV is shed at the start of the upstroke in (G). There is no evidence of spanwise flow.