Gryllus is a genus of field cricket (Orthoptera, Gryllidae, Gryllinae). Members of the genus are typically 15–31 mm long and darkly coloured. Until the mid-1950s, native field crickets in eastern North America were all assigned to a single species, Acheta assimilis Fabricius. Although regional variation in calling song and life history were noted, no morphological characters could be found to reliably distinguish these variants. Building upon the pioneering work of Fulton, Alexander used male calling song, life history and crosses between putative species to revise the taxonomy of gryllines in the eastern United States, and recognized five species, although at the time they were still classified in the genus Acheta.