The first males flew as early as 9 a.m., whereas the females usually showed their first activity at 10 a.m. During the midday heat the flight activity of both sexes decreased. Activity also decreased in the late afternoon (after 6 p.m.). After 8 p.m. no activity could be observed; the flies hung on stems of flowers and grasses or under leaves, where they stayed overnight. On cloudy days the first activity did not start until 10.30 a.m. and did not decrease during the midday period. D. diadema otherwise showed the same behaviour on such days, in contrast to other species which were less active. No distinction could be made between times of sexual activity and times of hunting. Oviposition was observed exclusively before midday.