Although crayfishes can locomote effectively on land, their walking performance may be affected by ambient temperatures and by their body size and hydration state. We used a racetrack timing system and videotaping to monitor the speeds, stride lengths, and stride frequencies of Orconectes rusticus in relation to body mass at temperatures of 15, 20, 25, 30, and 35°C. We similarly evaluated the locomotor performances of crayfish subjected to desiccating conditions at 25°C. Speed increased significantly with body mass with a scaling exponent of 0.18. This resulted primarily from a significant size-related increase in stride length. Walking speeds were greatest at the intermediate temperatures (25 and 30°C). This relationship was almost entirely due to thermally dependent adjustments in stride frequency. The crayfish were relatively intolerant of water loss, and locomotion ceased at a mean loss of only 9% of their initial body mass. Walking speed decreased significantly with increasing water loss, due almost entirely to a progressive reduction in stride frequency. The risk of desiccation is a serious constraint to sustained terrestrial locomotion. This is especially true for small individuals, although the risk, relative to that of larger animals, is lessened somewhat by the shallow scaling of the speed versus mass relationship. Crayfish might also lessen exposure risk by restricting overland movements to favorable climatic conditions (i.e., moderate to warm temperatures and high humidities).