Horse flies

Definition

Members of the family Tabanidae (order Diptera), comprising robust, fast-flying true flies whose females are obligate blood-feeders on mammals, including livestock, wildlife, and humans. Adults are diurnal, strongly attracted to sunlight, and possess scissor-like mandibles that inflict painful bites. Larvae are typically predatory or scavenging in aquatic or semi-aquatic habitats. The family is cosmopolitan except for polar regions and some oceanic islands. Horse flies are distinguished from the closely related deer flies (Chrysops and related genera) by their generally larger size, often patterned or unbanded eyes, and different host-seeking behavior.

Etymology

From the propensity of females to bite horses and other large mammals; 'fly' from Old English flēoge, denoting winged insects.

Example

In livestock management, female horse flies (Tabanus spp.) are significant pests: their painful bites cause defensive behaviors in cattle that reduce grazing time and weight gain, and they mechanically transmit equine infectious anemia virus and the filarial nematode Loa loa to humans in Central Africa.

Synonyms

• tabanids
• gadflies (loose, also includes botflies)

Related Terms

• Deer flies
• Tabanidae
• Diptera
• Hematophagy
• mechanical vector
• gadfly
• botflies

Usage Notes

In strict entomological usage, 'horse flies' refers specifically to the family Tabanidae, though the term is sometimes applied more narrowly to larger tabanid species in the genus Tabanus versus smaller 'deer flies' in Chrysops and related genera. The common name 'gadfly' is ambiguous: historically applied to both horse flies and botflies (family Oestridae), it is now less favored in technical writing. Horse flies are sometimes mistakenly conflated with stable flies (Stomoxys calcitrans, family Muscidae), which are smaller, have different mouthpart morphology (sponging-lapping versus cutting), and exhibit different resting behaviors. The claim that horse flies detect infrared radiation is erroneous; they locate hosts visually and through carbon dioxide and other chemical cues.