The biology and development of immature stages of summer (SR) and winter rainfall (WR) strains of Onitis caffer Boheman were studied in South Africa in a summer rainfall area (Pretoria). A pair of adult beetles buried up to 650 ml of dung from one dung pad, and females laid an average of 1 egg for every 62 ml of dung buried. Broods were buried at an average depth of 50 cm in watered soil and 24 cm in unwatered soil. Eggs laid in June (winter) hatched 10 weeks later. The third instar was reached by late October. WR larvae suffered higher mortality (82%) with the onset of summer rains than did SR larvae (53%). By the following June, 6% of surviving WR individuals had emerged as adults, 12% were adults in faecal shells and 82% were diapausing third-instar larvae. Of the SR individuals, 67% emerged by June and 33% were diapausing third-instar larvae. In a second experiment, two groups of broods of the SR strain of O. caffer of different ages were set out in the field in June. One group, equivalent to broods produced early in the season (March), entered diapause as third-instar larvae, and adults emerged the following autumn. The second group represented broods produced later in the season (May); the majority did not diapause, but adults also emerged the following autumn. A field population of SR adults of O. caffer was sampled for two years. Adults were first recorded at the end of February (late summer), and newly-emerged specimens were caught up until the end of April. Maximum numbers were recorded in late March to early April (autumn), and activity ceased in June-July (winter).