Seasonal patterns of abundance of Musca vetustissima Walker and scarabaeine dung beetles were measured at Busselton in south-western Australia for two years before and three years after, the introduction and establishment of two species of summer-active dung beetles, Oniticellus pallipes (F.) and Onthophagus binodis (Thunberg). Previously, only a single winter-active native dung beetle species, O. ferox Harold, occurred in this area. The mean dry weight of dung beetles trapped in December (early summer) was unaffected by the establishment of the additional species, and fly populations remained high. In January, however, dung beetle dry weight increased more than 60-fold and M. vetustissima abundance fell to 12% of its previous value, essentially halving the duration of major fly problems in the area. Virtually no flies emerged from cattle dung after December, when dung beetle activity reduced egg-adult survival of M. vetustissima to only 0·5%. It is proposed that better M. vetustissima control could be achieved in much of south-western Australia by introducing additional dung beetle species that are abundant in November and December.