We carried out a year-long survey of insects, using carrion-baited traps in the municipality of Campinas and five surrounding municipalities with different urbanization profiles, in southeastern Brazil. We studied the spatio-temporal variability and preferences for type of bait of three blow fly species that are forensically important in Brazil: Chrysomya albiceps (Wiedemann), Chrysomya megacephala (F.), and Lucilia eximia (Wiedemann). All three species preferred chicken. C. albiceps and L. eximia preferred the urban environment, while C. megacephala preferred the rural environment. Calliphoridae, Muscidae, Fanniidae, and Sarcophagidae were the most numerous families. No clear seasonal patterns could be recognized for the three species. The associations of species/municipality, species/environment, and species/bait are discussed from the ecological and forensic standpoints.