The female of Prosimulium flaviantennus (Stains and Knowlton) was originally described from Logan Canyon, Utah in 1940. In 1943 the same authors figured the genitalia of a male they considered to be of this species. No actual description of the male was given, and nothing on the biology was reported.

During the spring of 1956 and 1957 large numbers of larvae and pupae of the species were collecced by the writer. Reared pupae provided adults of both sexes. A redescription of the female and first descriptions of the male, pupa and larva, and notes on the biology and distribution of this species are presented below.