Figure 2.
(a) Schematic of the experimental set-up. Beetles are filmed through a mirror (M) by a high-speed camera (C) as they pursue a prey dummy in an arena (A) illuminated by two lamps (L). (b) Actual binary image of a tiger beetle pursuing a prey dummy automatically extracted from a digital frame. Our software finds the two fiducial white spots painted on the beetle and the centroid of the prey dummy (marked as grey crosses). From these three points, the angular variables with respect to an external Cartesian frame (X,Y) are calculated: the beetle's orientation θb, the error angle θe from the beetle's mid-sagittal plane (dotted line) and the prey's angular position θp.