Although hilltopping behavior has rarely been reported for crabronid wasps, three species of Tachytes wasps defend hilltop perch sites in central Arizona during the late summer. All three species (T. ermineus, T. spatulatus, and T. sculleni) can be found at the same hilltop during August and September and they perch in many of the same plants at this location. The three species are, however, spatially segregated to some extent in that T. ermineus perches very near the top of large shrubs and small palo verde trees on the hilltop, T. spatulatus perches somewhat lower within many of these same plants, while T. sculleni perches very close to or on the ground about the outer edges of shrubs growing on the hilltop. Males of all three species tend to be site faithful with marked males returning to their perch sites over several days. In experiments in which resident males of T. spatulatus were removed, the replacements that arrived to occupy the trees tended to be smaller, suggesting that large body size confers an advantage in the defense of perching sites in this species. The mating system of these species can be labeled landmark territoriality, with males defending visually conspicuous sites on hilltops that presumably attract receptive females to the territory holders.