This paper provides keys for females and males of the Nearctic Dasymutilla in the USA and Canada. It also provides notes on changes that have taken place since Mickel's (1928, 1936a) keys and Krombein's (1979) catalog of species. One new species, Dasymutilla fasciventroides Manley, Williams and Pitts, new species is described. Fourteen new synonymies are proposed: Dasymutilla arenivaga var. unicolor Mickel, new synonym under D. arenivaga Mickel; Dasymutilla dawsoni Mickel, new synonym under Dasymutilla nigripes (Fabricius); Dasymutilla formicalia Rohwer, new synonym under Dasymutilla erythrina (Say); Dasymutilla hispidaria Mickel new synonym under Dasymutilla calorata Mickel; Dasymutilla perilla perilla Mickel, new synonym and D. perilla gentilicia Mickel, new synonym under D. gorgon (Blake); Dasymutilla phaon fimbrialis Mickel new synonym under D. phaon (Fox); Mutilla Clio (sic) Blake, new synonym under Dasymutilla californica (Radoszkowski); Mutilla clytemnestra Fox, new synonym under Dasymutilla coccineohirta (Blake); Mutilla pacifica Cresson new synonym under Dasymutilla aureola (Cresson); Mutilla (Sphaerophthalma) (sic) Bexar (sic) Blake new synonym and Dasymutilla cassandra Mickel new synonym under Dasymutilla asopus (Cresson); Mutilla (Sphaeropthalma) Comanche (sic) Blake, new synonym under Dasymutilla occidentalis (Linnaeus); and Mutilla (Timulla) nigricauda Viereck, new synonym under Dasymutilla montivagoides (Viereck). Finally, the males of Dasymutilla dammersi Mickel and Dasymutilla flammifera Mickel, and the female of Dasymutilla imperialis Manley and Pitts are associated and described.