Proctacanthus milbertii (Macquart) Proctacanthus milbertii (Macquart, 1838): 124. Recognition characters: Brownish gray species; length 30–34 mm; mystax straw white; thorax brown pollinose with 3 brown pollinose stripes dorsally; scutellar setae white, bristles mostly black or mixed black and a few white; wings with brownish aspect; abdomen brownish gray pollinose, setae and bristles on first three abdominal segments partially black; legs brown, femora black anteriorly. Distribution: FREMONT: near Lander, 1,524 –2,438 m (5,000 –8,000 ft), July 1895 (RO-UK). PLATTE: Dwyer, 18 Aug. 1960, 11 Aug. 1961 (RJL, REP); Glendo, 14 Aug. 1958 (DRT), 18 Aug. 1959, 23 July 1960, 1–23 Aug. 1961, 17 Aug. 1962 (RJL); Guernsey, 27 July–12 Aug. 1960, 27 July–31 Aug. 1961, 9 Aug. 9–13 Sept. 1962 (RJL); Wheatland; 14 Aug.–2 Sept. (SD, RJL); Lance Creek, 24 Aug, 1895 (?- FDA); 16 km W of Wheatland, 6 July–7 Sept. 1964 (FRH, RJL); 2 Sept. 1965 (RJL). Recorded from Wyoming by: Dennis & Lavigne (1975) (as Proctacanthus micans); Fisher & Wilcox (1997) [entire United States, except absent Oregon, California, Nevada, Utah, and northeastern states (Maryland northward)]; Geller-Grimm (2018); Lavigne et al. (1994). Habitat: Sagebrush steppe shrub and grassland and grama-needlegrass-wheatgrass grassland vegetation types. Open rangeland, short, mid-grass plains area; shows decided preference for downy cheatgrass (Bromus tectorum L.) areas in shallow valleys. Ethology: Rests on and forages from soil, prickly pear cactus, tall weeds and cheat grass (see Dennis & Lavigne 1975 as Proctacanthus micans). Prey: DIPTERA: Asilidae: Efferia bicaudata (Hine), Guernsey, 16 Aug. 1961 (two records), Guernsey, 15 Aug. 1962, Wheatland, 7 Sept. 1964; Ospriocerus latipennis (Loew), Dwyer, 20 Aug. 1959. HYMENOPTERA, Bombidae: Bombus sp. (three records). ORTHOPTERA, Acrididae: Melanoplus sanguinipes (Fab.) Wheatland, 18 Aug. 1964. COLEOPTERA, DIPTERA, HEMIPTERA (Heteroptera), HYMENOPTERA, LEPIDOPTERA, NEUROPTERA, ORTHOPTERA (see Dennis & Lavigne 1975 as Proctacanthus micans; Lavigne & Pfadt 1966; Lavigne et al. 1994).

Published as part of Lavigne, Robert J. & Dennis, Steve, 2019, Robber flies (Insecta: Diptera: Asilidae) of Wyoming, USA with keys to genera and species, pp. 1-126 in Zootaxa 4662 (1) on page 58, DOI: 10.11646/zootaxa.4662.1.1, http://zenodo.org/record/3383448