When forced by prodding to run continuously, Centruroides hentzi (Banks 1901) (Scorpiones, Buthidae) lost over 70% of initial speed within 30 s and moved fitfully, if at all, after 90 s. A lack of behavioral response to alternative stimuli presented after two mins of prodding suggested that the scorpions were physiologically fatigued. Mean whole body D-(-)-lactate concentration increased from resting values of 0.6 μmol/g to 4 μmol/g at exhaustion, an approximately 6.5-fold change. It is unlikely that scorpions accumulate significant amounts of other anaerobic products. Whole body lactate accumulations in C. hentzi are lower than those found in species of spiders, crabs and terrestrial ectothermic vertebrates that are more specialized for running. This difference may be the result of proportionately more non-locomotory body mass in the bodies of scorpions compared to these other animals and not due to lower rates of anaerobic metabolism within locomotory muscles.