The population dynamics of Ommatoiulus moreletii were studied in an open grassland and a dry sclerophyllous woodland in South Australia. During summer, O. moreletii aggregated in cool, moist sites (e.g. beneath tussocks of Lomandra fibrata (Liliaceae)) or burrowed underground. In autumn, the animals surfaced and dispersed. In a particularly hot and dry summer, mortality was demonstrated in the grassland but not in the woodland which was relatively cooler and moister. The survival of females from an autumn breeding season to the subsequent spring was inversely correlated with their maturity in autumn. The advantage to O. moreletii of survival of females after a poor breeding season is discussed with reference to den Boer's (1968) concept of “spreading of risk”.