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Early drying of pools on a granite escarpment in subtropical south-eastern Botswana is a major threat to pool biota through abortive hatching. The fairy shrimp Branchipodopsis wolfi is a striking inhabitant of these small rock pools. Both in the laboratory and in the field, egg bank characteristics have been noted which may aid in the species persistence in this unpredictable environment. Delayed hatching of part of the egg bank may serve as a hedge against subsequent drought-related reproductive failure. Under laboratory conditions (27 degrees C), hatching continued for 16 hydration/drying cycles. Emergence was cued by light, conductivity and temperature. Within a temperature range of 5-30 degrees C, maximal hatching (up to 80 %) occurred at 15 degrees C, which is below the average temperature (27/28 degrees C) during the rainy season. Low hatching (<10%) at natural average temperatures probably reflects limited averaged chances for successful recruitment. Only at sub-optimal temperatures for hatching was there a significant negative effect (p < 0.05) of increasing conductivity in the natural range of 5-60 mu S/cm. Low temperature and conductivity values, which occur when pool basins fill, are reliable cues for synchronising the life cycle of B. wolfi to the short suitable growth period. Eggs, furthermore, only responded to the initial incubation temperature, restricting hatching to the early phases of filling or dilution with additional rains. Extra hatching of immersed eggs or dried eggs on the edges of the pools was associated with a decrease in conductivity after additional rainfall. In spite of the frequent nightly rains, emergence is almost entirely inhibited in darkness. This light requirement is believed to prevent hatching of buried eggs as confirmed by laboratory simulations. Egg banks with conditional responsiveness to cues, restricting hatching to initial or additional rains, result in an association between hatching and the likelihood of completing a life: cycle.