Amsterdamse Waterleidingduinen, the Netherlands; 24 May 2009.
A considerable number of these flies were constantly flying around a large Poplar trunk.
Upon meeting a resting fly, the males started courtship behavior; occasionally, this was directed towards another male (top left).
A courting males stand high on his legs, and his wings vibrate; he moves the front legs in large arcs such that the the broadened distal
ends of the tarsi move around the female's head, as if to mesmerize her (top right). After some time (approximately 10 seconds), the male
starts to descend (bottom left); during descend, he puts the broadened patches of the tarsi at the wing base of the female (bottom middle). Finally, when the
male's head is below the female's wings, the male bends his abdomen upward, and tries to contact the females genitalia, to
couple with her (bottom right). I didn't see any successful attempt though.