Questions: (1) Are the geographic clines of sex-determining factors in the housefly of the northern hemisphere mirrored by similar clines on the southern hemisphere? (2) What climatic factors can best explain the geographical distribution of sex-determining factors in the housefly? Data: Frequencies of sex-determining factors of houseflies collected in Africa and corresponding literature data on houseflies studied on other continents. Global climate data from public databases. Results: Housefly populations on the southern hemisphere repeat the pattern earlier found on the northern hemisphere: higher frequencies of autosomal M and F^D factors closer to the equator. Seasonality in temperature variation is the best predictor for the distribution of the male sex-determining factor, whereas female sex-determining factors are best explained by variation in humidity and yearly mean temperature.