Adults and larvae of Coproica lugubris and Chaetopodella scutellaris (Diptera: Sphaeroceridae) occur in great numbers on cow droppings. Courtship behaviour and copulation were analyzed and compared. Striking differences were found in the complexity and number of courtship patterns. In contrast to C. lugubris, where males usually mount females without performing any displays, courtship of Ch. scutellaris is rather complex: a male approaches a female and positions himself facing her; he then starts to circle her in a fashion very similar to a male courtship pattern in Drosophila species. Females usually respond to circling with a typical behaviour pattern I called swaying. Its function is discussed. The complex courtship behaviour of Ch. scutellaris is interpreted as a mechanism for female choice. In Ch. scutellaris copulation takes about 60 min longer than in C. lugubris, but the mechanism based upon this obvious difference is not understood. Females of both species can effectively prevent males from copulating.