Horse Fly

Horse flies make up the genus Tabanus within the family Tabanidae, a group of large, robust flies found on every continent except Antarctica. They are among the biggest and strongest-flying true flies, easily recognized by their bulky build and large, often brilliantly patterned compound eyes.

Only the females feed on the blood of mammals, which they need to develop eggs, while males restrict themselves to nectar and plant fluids. Horse flies are strong, direct fliers capable of covering long distances quickly, and their larvae are predatory, playing a role in regulating other invertebrate populations in wet soil habitats.

• Large, heavy-bodied fly, typically 15–25 mm long, noticeably bigger and bulkier than a house fly.
• Enormous compound eyes that often shimmer with green, gold, or rainbow iridescence, especially in females.
• Body usually dark gray, brown, or black, sometimes with pale stripes on the abdomen.
• Single pair of clear or smoky wings held flat over the back at rest; strong, direct flight with an audible buzz.
• Lookalike: the smaller deer fly has patterned wings and a more slender build; horse flies are larger and heavier overall.

Common worldwide in temperate and tropical regions, especially near pastures, wetlands, ponds, and wooded edges where livestock or wild mammals congregate. Most active on warm, sunny days from late spring through late summer, particularly around midday.

Female horse flies use bladelike mouthparts to feed on the blood of large mammals, an important protein source for egg development; males instead feed on nectar and pollen. Larvae are predatory, living in wet soil or mud along pond and stream edges, where they hunt small invertebrates. Adults are strong, agile flyers and can be persistent around a chosen host, circling repeatedly before landing.

Horse flies undergo complete metamorphosis. Females lay clusters of eggs on vegetation overhanging water or moist soil; larvae hatch and drop into the wet substrate, where they develop through several molts over months to a year while preying on other small organisms. Pupation happens in drier soil nearby, and most species produce one generation per year, overwintering as larvae.