At the University of California Hopland Field Station in Mendocino County, six species of hematophagous Symphoromyia attacked the Columbian black-tailed deer, Odocoileus bemionus columbianus, during the months of transition (April through June) from the rainy season to the drought season. Between 1964 and 1966, S. pachyceras, S. cervivora, S. inconspicua, S. nana, S. trun-cata, and S. sackeni had similar seasonal patterns of abundance, with each present 6 to 10 weeks.

Minimum temperature thresholds at which Symphoromyia attacked were determined for five species. The upper temperature threshold for attack by S. sackeni was between 34.4 and 37.2°C. Diverse wind and light conditions had little effect on the host-seeking behavior of the species studied.

Symphoromyia attacking deer were seldom attracted to hosts other than deer, and only S. sackeni and S. pachyceras fed on other hosts. The seasonal occurrence of snipe flies coincided with the annual spring shedding of winter pelage by the deer and, in bucks, with the growth of antlers. All Symphoromyia attacked only the face, ears, or antlers of deer after relatively direct approach, and most species engorged within 1 to 3 minutes. There was a direct relationship between snipe flies feeding on the ears and face and the more rapid loss of the woolly underhairs at these sites. The tilted posture of feeding snipe flies that angled the body upward between and above raised guard hairs permitted feeding on the outer ear surface, a site where most other blood-sucking flies are repulsed by the sensory guard hairs.

The number of Symphoromyia attracted to an individual deer and to the face or ears of an animal varied greatly. The tolerance to flies and the anti-biting fly behavior of individual deer (ear flicking, brushing flies from the face, and reducing the silhouette by lying down, lowering the head, flattening the ears, and extending the legs) contributed to variations in numbers of snipe flies on and around the hosts.