Taxonomy 264 Morphology 265 Life History 266 Behavior And Ecology 268 Public Health Importance 271 Veterinary Importance 273 Prevention And Control 275 References And Further Reading 276

Because of their fairly large size, striking appearance, and diurnal biting habits, horse flies and deer flies (Fig. 13.1) are familiar to most people who have livestock or engage in outdoor activities. Diversity within the family is greatest in the tropics, but moist temperate regions typically have a rich fauna as well. Tabanids are present on every continent except Antarctica and have managed to colonize remote islands such as the Galapagos and the Melanesian Archipelago. Large seasonal populations of some species occur as far as 60° N latitude, but they disappear above the tree line.

The eyes of many species, when alive, are brilliantly patterned with shades of green, yellow, orange, and violet. Some species with strikingly green eyes are commonly called greenheads, and others are called yellow flies due to their yellow bodies. The blue-tail fly of American folk music probably was Tabanus atratus, a large black species which has a blue cast to the abdomen. Common names also may reflect times or places where these biting flies are found, but the source of some terms is obscure. Cleg, breezefly, whamefly, marcbfly, May fly, and mango fly are but a few of the many colloquial names used. Other common names, like bulldog and gad-fly, reflect the persistent annoyance of tabanids in seeking a blood meal.

The term horsefly is applied to relatively large species of tabanids, typically 10—30 mm in length. They are a serious nuisance to livestock and can mechanically transmit several significant animal pathogens, including those which cause surra, anaplasmosis, and equine infectious anemia. Even moderate numbers of flies feeding on livestock can result in significant production losses. A few horse flies readily bite people, examples being the infamous greenheads(T. nigrovittatusand T. simulans) in the coastal regions of the eastern United States.

The smaller tabanid species called deer flies typically are 6—10 mm long. In contrast to horse flies, they frequently attack humans. Fortunately, there are just a few human diseases known to be associated with deer flies. The most important tabanid-transmitted human diseases are loia-sis and tularemia. Outdoor activity and tourism suffer in areas where tabanid populations are high, although such losses are hard to quantify.

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