Fig. 4. Downward velocity maps at two cross sections around a hovering fruit fly at mid down- and upstroke. (A) Schematic diagram of the two cross sections around the hovering fruit fly, showing the position of velocity maps at the two cross sections at mid down- and upstroke (B–E). (B,C) Velocity maps at the plane parallel to the X-axis (a–a'); (D,E) Velocity maps at the plane parallel to the Y-axis (b–b'). Color of vectors indicates magnitude of downward velocity.