The ontogeny of aggressive behavior was studied in the flesh fly, Sarcophaga crassipalpis. Male flies were collected the day of adult emergence and kept in individual isolation chambers. Pairs of 1-, 2-, 3-, 4-, and 6-day-old, socially naïve flies were released into a circular arena and video recorded for 1 hour. An ethogram was constructed from the video recordings and used for analyses. Young flies differed from older flies in the types of aggressive behaviors that they exhibited in these dyadic interactions. Young flies tended to employ low intensity aggressive behaviors during encounters with conspecifics whereas older flies tended to escalate aggressive behavior to the highest intensity level more quickly and frequently than young flies.