The response of female canyon flies (predominantly Fannia conspicua, a member of the F. benjamini complex) to carbon dioxide (CO2) was examined at a site with a high prevalence of these flies. Females were collected using CDC-type suction traps without the light on 4 days during June and July of 2003 when fly populations were high. Traps were baited with one of the following potential attractants: CO2, water, milk bait, egg bait, limburger cheese, rabbit feces, ethanol, or nothing. Female F. conspicua showed a strong response to the presence of CO2 with a much lower or no response to each of the other treatments. The strong response of these flies to the presence of CO2 might be utilized in a trap-out strategy to reduce the numbers of and associated nuisance caused by these flies. Field collected canyon flies were also colonized in the laboratory and provided various substrates on which to lay eggs. True development sites of these flies are unknown. A discussion of these trials will be provided.