Cuterebra are robust flies, which in flight resemble large black bees. Little is known about the bionomics of most of the species included in this genus. Nearly all members of this group parasitize rodents and lagomorphs. Some species have a wide host range, others seem to be specific or semi-specific to a single host. Accidental parasitism of animals other than specific host animals does occur. In such cases the larvae or the host usually die before the larvae can mature. There is a wide variation in the effect of of the parasite on its host. If the parasite is found in a natural host, the ability of the host to tolerate the parasite is much greater. In chipmunks one to three parasites have no apparent effect but with four to nine parasites in one animal, there is a loss of weight and a decrease in activity. Occasionally death results from parasitism by Cuterebra. A valid key to the species of this genus does not exist. It is the purpose of this paper to establish a valid key for the described species of Cuterebra found in Utah and the neighboring states and to furnish descriptions of these species, which in conjunction with the key will aid the reader in identification of Cuterebra specimens. Whenever possible the host or hosts associated with each species will be listed. Within the genus Cuterebra there are several species complexes. As used here, complexes are supposedly intraspecific groups which have several major characteristics in common but differ on a few minor points. Only more detailed studies on the members of these complexes will indicate the extent of intraspecific variation and the delimitation of a true species.