Musca autumnalis DeGeer were collected in the summer and fall of 2011 and 2012 from a beef cattle herd in southern California. Visual counts of Musca spp. on cattle faces were documented, and sweep net samples of face flies and other Diptera were also collected from cattle faces. Face flies dominated in the net collections, and 5–30 flies per face were common between early July and October 2011. Adult female M. autumnalis were dissected and examined for the presence of the host-specific nematode Paraiotonchium autumnale (Nickle). Overall, 67 of 887 (7.6%) adult face fly females were parasitized. M. autumnalis' ability to survive in such a southerly latitude (34° N) could reflect the rather temperate weather (coastal effects) and frequently irrigated pastures at the experimental site in southern California. Preliminary observations suggest that face flies disappear from cattle during winter, despite generally favorable temperatures for fly activity. This is a possible indication of diapause and should be examined further.