Courtship dances in the flies of the genus Lispe (Diptera: Muscidae): from the fly's viewpoint.

Two predatory fly species, Lispe consanguinea Loew, 1858 and L. tentaculata DeGeer, 1776, inhabit the supralittoral zone at the shore of a fresh-water reservoir. Both species look alike and possess similar "badges," reflective concave silvery scales on the face. Flies occupy different lek habitats. Males of the first species patrol the bare wet sand on the beach just above the surf. Males of the second species reside on the more textured heaps of algae and stones. Courtship and aggressive behaviour of males was video-recorded and analysed frame by frame. Visual stimuli provided by the conspecific partner were computed in the body-fixed space of a fly observer. Males of L. consanguinea perform long pedestrian dances of pendulating circular arcs (frequency 2 s(-1), median radius 2.5 cm, linear velocity 0.130 m/s). Right and left side runs are equally probable. Circular runs are interrupted by standby intervals of average duration 0.35 s. The female views the male as a target covering 2 by 2 ommatidia, moving abruptly with the angular velocity over 200 degrees/s in a horizontal direction down the path of about 50 degrees till the next standpoint. Dancing is evenly distributed around the female. On the contrary, the male fixates the image of the female within the narrow front sector (median +/-10 degrees); the target in his view has 6-7 times less angular velocity and angular span of oscillations, and its image in profile overlays 6-8 by 2 ommatidia. If the female walks, the male combines tracking with voluntary circular dances. Rival males circle about one another at a distance shorter than 15 mm, but not in close contact. Males of L. tentaculata are capable of similar circular courting dances, but do so rarely. Usually they try to mount any partner immediately. In the latter species, male combat consists of fierce wrestling. Flies of both species often walk sideward and observe the partner not in front but at the side. 2006 Wiley-Liss, Inc.