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The influence of moonlight on the foraging behaviour of the scorpion Buthus occitanus israelis was observed. In contrast to their visual predators, most scorpions use air and surface vibrations to locate their prey. Therefore, moonlight is not likely to have a direct effect on the scorpions’ foraging behaviour, but rather an indirect effect through changes in risk from predation or changes in prey availability. Adult scorpions were less active on moonlit nights than on dark nights, and adults that were active on full moon nights tended to ambush under bushes. Juveniles, however, did not seem to alter their activity as a response to moonlight. Mass-to-size ratios of adult scorpions foraging on moonlit nights were significantly lower than those of scorpions foraging on dark nights, suggesting that scorpions that forage in bright moonlight are individuals with relatively low energy reserves. The results are consistent with the hypothesis that risk of predation is higher during periods of bright moonlight. It is suggested that the scorpions use environmental factors such as illumination and humidity as proximal cues, to evaluate levels of predation risk and food availability. (C) 1996 The Association for the Study of Animal Behaviour.