The northern crayfish Orconectes virilis is a nuisance aquatic species thought to have entered Arizona through bait-bucket introductions. Arizona is one of the few states that has no native crayfish. The negative effects of nonindigenous crayfishes on native flora and fauna are well documented. Crayfish can significantly reduce the abundance of macroinvertebrates, aquatic vascular plants, and mollusks. Crayfish can prey on vertebrates such as juvenile Sonoran mud turtles, all life stages of leopard frogs Rana Chiricahuensis except eggs as well as newborn garter snakes. Crayfish can also compete with and prey on many fish species, such as Little Colorado spinedace Lepidomeda vitatta, and rainbow trout Oncorhynchus mykiss. Investigations of crayfish control methodologies, and the effects of crayfish on native flora and fauna are critically important for managing native aquatic species. The efficacy of various currently available control methods and effects of this species on native Arizona fish and wildlife have been previously reported. However, little is known about the life history and tolerances of the crayfish itself, especially those life history characteristics that might make it vulnerable to control in Arizona. Most life history information about the northern crayfish comes from studies of northern lakes. Previous Arizona studies include investigations of its diet and other effects, and autumn distribution according to water temperature. Although northern crayfish has had considerable impact on native ecosystems where it has invaded, few control techniques have been successful for controlling this species. Techniques for suppressing crayfish can be extremely labor intensive, costly, or ineffective. Therefore, knowledge of vulnerable stages of the life history of the northern crayfish would be important to identify where control methods can be applied to maximize the impact to their populations with the most cost effectiveness. We had two objectives for this study: (1) to examine specific life history and tolerances of the northern crayfish in Arizona and (2) to use these life history and tolerances in a model to identify susceptible life stages that would the most promising to target for control. Field work on this project was completed and a final report was written in 2009. Results are now being prepared for publication.