Fig. 2. Measurement of induced air flow in a flight chamber. (A) Two anemometers, an axial inflow anemometer and a radial outflow anemometer, placed between the antennae and behind the wings at roughly 3/4 of the wing length from the base, respectively, recorded the induced airflow due to the flapping wings. An optical force sensor simultaneously recorded the vibrations generated by the flapping moth on its tether. A computer-controlled visual display motivated the moth to fly and modulate its wing kinematics. In the experiments reported here the visual display was turned off after the moth initiated flight and the chamber was left dark. (B,C) The frequency peaks of the vertical measurements and the two anemometric records (only axial inflow data are shown) always matched the primary stroke frequency (asterisks) and a secondary peak at double stroke frequency.