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Diurnal activity of host-seeking "canyon flies" (Fannia benjamini complex) (Diptera: Muscidae) was determined on a warm, sunny day during their peak seasonal activity period (early July) in the coastal mountain community of La Habra Heights in Los Angeles County, California. High levels of activity persisted for several hours in the morning and evening, but peak abundance was within an hour after sunrise and an hour before sunset, when >600 flies (mainly Fannia conspicua Malloch) could be collected in 5 min from a person using a sweep net. Host-seeking activity was low during midday hours, when flies apparently were seeking shelter from the heat, and activity ceased after sunset. Potential bait materials, including some known to elicit a response by other host-seeking Diptera (water, rabbit feces, egg bait, milk bait, Limburger cheese, ethanol, and CO2) were tested for "canyon fly" response using CDC-type suction traps (without light). CO2 resulted in significantly higher capture of female "canyon flies" (up to approximately 2,000 flies per trap in a 6-h period) relative to traps baited with other materials or with no bait. Host-seeking activity in relation to distance from a putative developmental site was evaluated. The proportional capture of flies in CO2-baited suction traps was significantly explained by distance from a residential area planted with Aptenia cordifolia (L.) (Aizoaceae; red apple), a ground cover plant that is a developmental site for F. conspicua. Proportional trap capture rapidly decreased as distance from the residential area increased. Implications of these studies for "canyon fly" control are discussed.