Class Insecta
Order Diptera
Family Tabanidae
Subfamily Chrysopsinae (Chrysops sp.)
Subfamily Tabaninae (Tabanus sp.)

Deer Flies and Horse Flies

Biting flies are distributed throughout the world and, apart from nuisance biting, some are responsible for the transmission of diseases in humans and livestock in many countries. Although biting flies (other than the mosquitoes) rarely transmit diseases to humans they are renowned for painful bites and annoying habits during the summer months in general.

Within North America, the biting flies of greatest significance are the deer flies and horse flies (Family Tabanidae), the stable flies (Family Muscidae) and the black flies (Family Simuliidae), as well as the biting midges or sand flies (Family Ceratopogonidae) and the mosquitoes (Family Culicidae). Compared with some other countries, black flies are usually not a concern although occasional problems do occur.

Tabanid flies are widespread throughout the warmer parts of North America and will attack humans, livestock and domestic pets to acquire blood. The flies are stoutly built and are strong swift fliers that tend to be more active throughout the summer months especially in still, open sunny areas. The Tabanids, especially, are influenced by weather and will respond to changes in barometric pressure, wind, cloud cover and temperature.

Stomoxys calcitrans is a vicious biter with piercing and sucking mouthparts that can easily penetrate socks and stockings. Both sexes of this fly will search for blood meals, often twice a day, and can engorge on blood up to three times their own body weight. In the cooler months their life span is 1-2 months, in warmer weather it is reduced to 3-4 weeks of adult life. These flies are seldom found in urban situations (except where horse stables or major composting areas are nearby) and are more often associated with rural properties and domestic animals; they are also common on some beaches where they breed in sea-weed. They have been known to enter homes and other buildings to blood feed during daylight hours.

Tabanids have two large prominent eyes and are much larger and robust than Stomoxys calcitrans; they have a shorter life than Stomoxys calcitrans and an adult lives only 3-4 weeks. Although they are a major pest of livestock, several species will bite people. It is only the females that seek blood meals; the males feed on nectar and plant juices. Female tabanids are armed with two large blade-like mouthparts, that are used to pierce and slash skin. This inflicts a painful wound and produces a large puncture site that will continue to ooze blood long after the mouthparts are extracted. As the blood flows, the flies lap the blood to engorgement, unless disturbed. It has been estimated that some animals can loose up to 300ml of blood a day due to attack by these flies, resulting in serious blood loss. Adult tabanids are cosmopolitan but are more abundant in moist forests and woodlands. After mating, the females disperse, traveling many kilometers in search of blood meals. Tabanids are pests throughout summer and are a continual nuisance at outdoor activities, particularly near water.

Biting flies can produce an array of symptoms including pain, itching, urticaria and cellulites. An allergic response is the most common, which may be characterized by hives, and in some cases wheezing. Tabanid bites are very painful, with some individuals developing severe lesions, fever and general disability. This allergic response is due to the large amounts of saliva injected by the fly to prevent their blood meal from clotting. Stable flies bites are quite painful and they produce small papules that quickly fade, but are often itchy. Local symptoms can be relieved with an application of antiseptic lotion or cream and in some cases a mild oral antihistamine is prescribed. Prolonged scratching of bites may lead to secondary infections. Hypersensitivity to biting flies is rarely seen in human population.