Nerax aestuans (Linnaeus) Asilus aestuans Linnaeus, 1763: 413. Recognition characters: Grayish-black species; length 18–20 mm; mystax black above, white below with few black bristles on oral margin; bristles and setae of mesonotum largely black with white setae posteriorly; meral bristles black in both sexes; scutellar setae white, marginal bristles black; males with abdominal segments 5–7 silvery white pollinose, sternite 8 produced apically with long black setae; legs, femora black, tibiae brown fading to black apically. Distribution: Recorded from Wyoming by Cole (1969) (as Efferia aestuans); Fisher & Wilcox (1997) (as Efferia aestuans); Geller-Grimm (2018). Habitat: Sagebrush steppe and wheatgrass-needlegrass shrub steppe shrub and grassland, and grama-needlegrass-wheatgrass, grama-buffalo grass, and wheatgrass-needlegrass grassland vegetation types. Ethology: Nothing known. Prey: None known.

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 38, DOI: 10.11646/zootaxa.4662.1.1, http://zenodo.org/record/3383448