Fig. 1. The arena for tethered flight. The moth was tethered behind a translucent screen subtending 180° at the eye. A pattern of horizontal stripes was projected onto the screen and moved vertically by a computer-controlled servomotor (not shown). A laser system (inset) tracked up–down displacement of the tether and was calibrated to net vertical force (lift); an LED/photodetector pair tracked fore–aft displacement and was calibrated to horizontal force (thrust). A laser beam focused into a two-dimensional ‘sheet’ of light was cast across the abdomen onto an optoelectronic sensor to track angular deflections of the abdomen. A CCD camera was oriented orthogonal to the longitudinal axis of the moth and recorded wing motion at 500 frames s^–1.