The behavioral effects of heavy metals on crayfishes may significantly affect their survival in the environment. Changes in their ability to remain under cover could substantially decrease their survivorship due to increased predation. The effect of sublethal cadmium exposure on the ability of juvenile crayfish to remain in cover was evaluated. Four different treatment groups were used (N=11 juveniles each): a control group (not exposed to cadmium), and three experimental groups exposed to 1, 2, or 3 mg Cd/L for 7 d. Crayfish were placed, individually, into glass aquaria containing 3 L of laboratory water pre-treated to detoxify all heavy metals, with continuous aeration. Each crayfish was provided with a dark, thigmotactic shelter. Cadmium was introduced into the aquaria on days 1 and 4 to maintain the nominal concentrations. Beginning on day 5 and continuing through day 7, observations were taken on each crayfish five times per day, with a minimum of 30 minutes between observations. Crayfish position was recorded as in cover or in the open area of an aquarium. Juveniles in the control groups were in cover 78.3% of the observations. Over the 3 d of observations, juveniles in the 1 mg Cd/L exposure groups used cover 72.1%. Those in the 2 and 3 mg Cd/L groups used cover 53.9% and 60.0%, respectively, indicating hyperactivity induced by cadmium exposure. Examining the daily results, however, those juveniles in the 1 mg Cd/L group were in cover only 60.0% of the time by day 7, indicating a latency to produce hyperactivity at this concentration. Those in the 2 mg Cd/L group were using the covers similarly to the controls by day 7 of exposure, indicating habituation to the cadmium or “exhaustion” of the animals by hyperactivity. Those in the 3 mg Cd/L group behaved similarly to controls on day 5, but beginning on day 2 and continuing into day 3 of the observations spent progressively fewer of the observations in cover, suggesting that initial hyperactivity occurred prior to the beginning of observations, and “exhausted” the animals, or that they were severely traumatized by the exposure to 3 mg Cd/L and required time to recover before exhibiting hyperactive behavior.