Musca fergusoni J. & B. is an indigenous Australian fly that infests livestock, feeding on sweat and other body secretions and breeding in cow and horse dung. The fly is larviparous, developing a single larva at a time and depositing it at the end of the first instar. The ovaries comprise two ovarioles each, and the single ovulations alternate between ovaries and between ovarioles within an ovary. Abnormalities of development shown by unfertilised females are described, including the accumulation of fluid around unhatched eggs in the uterus which suggests that there is intrauterine secretion of nourishment for the larva. Descriptions are given of the immature stages. The egg is adapted for life in utero by having the respiratory plastron confined to the posterior end, oriented towards the genital aperture of the mother. The puparium is whitish, and is hardened by calcification instead of tanning. The durations of development at 16, 20, 27 and 32°C are given: from larval deposition to moult to third instar takes 58, 38, 19 and 15 h, respectively; from larval deposition to pupariation 11·5, 7·5, 3·5–4 and 3–3·5 days, respectively; and from larval deposition to adult emergence 53–57, 31–33, 15·5–16·5, and 10–11 days, respectively.