Canyon flies are serious human pests, particularly in coastal California mountain areas. Seasonal adult activity was monitored by netting from humans at 1-2 week intervals from April 2003 through July 2004 in La Habra Heights (coastal mountains). Additional observations were made in Woodcrest near Riverside (inland mountains). The dominant species is Fannia conspicua, but some F. benjamini have been collected as well. Some adult activity was evident year-round at both sites. Bimodal diel activity (morning and evening) was documented during peak abundance in late June and early July, when over 600 flies (essentially all females) could be collected from a person in 5 minutes in La Habra Heights. Males were observed swarming in small groups at heights of 0.5-4.0 meters. Adult flies collected in the wild in mid-July survived up to 4 months in the laboratory.