>40 spp. in our area, incl. several undescribed
Most recent key to Nearctic species of Chlorops was made by Becker in 1912 (in German)(1)
There are a few dozen described species. Some of them are almost certainly synonyms but there are also undescribed species. The last revision was by Becker in 1912, and it fails to account for the true amount of variability within a species. Important characters for sorting are: stripes on scutum black or red; pleura heavily marked, with one spot, or plain yellow; ocellar triangle mostly yellow, yellow with an anterior black spot, yellow with corners dark, black with yellow sides, or entirely black; palps black or yellow; clypeus yellow or with black stripe; legs almost entirely yellow (cf. sulphureus), or yellow with black markings; abdomen with sharply defined black bands, overall yellowish, or overall dark; amount of black on first flagellomere (sometimes variable within a species); arista black, white with thickened yellow base, or otherwise.
often very similar to Thaumatomyia in colour pattern, but the scutellum is more convex on top in Chlorops, and very flat with a sharp margin in Thaumatomyia. Also, there are a few Chlorops with the distinctive pattern on the triangle on top of the head (dark round spots fore and aft on a pale background). --Terry Wheeler