Abstract
The robber fly Cyrtopogon willistoni Curran was studied in SW Montana, where it was an opportunistic predator of relatively small insects from 25 families in 7 orders. The most common prey were Diptera (44%) and Homoptera (21%), with Cicadellidae, Bibionidae, and Formicidae comprising 44% of the prey. The elaborate courtship behavior of males included audible airborne visual displays that made use of silvery-white combs of hairs on the males' foretarsi. While perching, the flies exhibited both lateral and dorsal basking postures, and were apparently capable of strong flight only when direct sunlight was available. I compare the foraging and courtship behaviors of C. willistoni to those of other Cyrtopogon, and their thermal responses to those of other robber flies in the same habitat.