A SEASONAL BITING FLY IN SAN MATEO COUNTY
Snipe flies, from the Family:
Rhagionidae, are 4.5 to 15 mm long stout bodied flies that can range in color from black to brown and yellow. Though most snipe flies are predators of other insects, one genus (Symphoromyia) has adapted to feeding on mammal blood.
Similar to mosquitoes, only adult females will seek out and bite hosts. Typical hosts can include a number of mammals such as deer, cattle, horses, dogs, and humans. Bites on humans usually occur around the face and neck, but are also common on the front and back of the hands. The bite of a snipe fly is painful, most likely because its slashing/sponging mouthparts are similar to closely related Tabanid flies (horse flies and deer flies). The bite can cause moderate to severe inflammation and small droplets of blood can pool at the bite site.
The snipe fly blood feeding process usually takes 30-35 seconds, in which 5-6 mg of blood is extracted. During this time, the tarsi of all six legs are in contact with the host and the fly positions its body at a 45° angle until its abdomen begins to fill with blood and droops to nearly horizontal.
Because of the intermittent probing and feeding interruption that can occur when attempting to take a blood meal, snipe flies have been pinned as a possible vector of tularemia and similar diseases, but there has yet to be any definitive connection between snipe fly bites and disease transmission of any type.
In California, snipe flies live in mountainous and coastal regions and are active from April to mid-July. Larvae of blood feeding snipe flies live in soil and moss, where they are predators of other dipteran larvae. San Mateo County Mosquito and Vector Control District lab staff have collected adult specimens in carbon-dioxide baited traps from woodland and grassy areas in and around Portola Valley.