Deer Fly

Deer flies form the genus Chrysops in the family Tabanidae, the same family as horse flies, though they are noticeably smaller and more colorfully marked. They are found across most of the world and are easily distinguished from their larger relatives by the bold dark patterning on their wings.

Like horse flies, only female deer flies seek out blood meals to fuel egg production, while males feed on nectar and pollen. Their larvae develop in wet, muddy habitats where they act as small predators, contributing to the food web of wetland and streamside ecosystems.

• Small, compact fly, 6–10 mm long, smaller and more streamlined than a horse fly.
• Wings marked with bold, dark brown or black bands or patches, a key identifying feature.
• Eyes often bright green or gold with intricate patterning, especially vivid in life.
• Body typically black or dark brown with yellowish markings on the abdomen in some species.
• Lookalike: distinguished from horse flies by its smaller size and patterned wings, and from house flies by its larger eyes and heavier build.

Widespread across North America, Europe, and Asia, deer flies favor wooded areas, trails, marshes, and habitats near slow-moving or standing water. They are most active on warm, still days in late spring and summer, often flying low around the head and shoulders of passersby.

Female deer flies locate hosts using vision and body heat, circling persistently before landing to feed on blood, which supports egg development; males instead visit flowers for nectar. Larvae are semi-aquatic predators living in mud and decaying vegetation at pond and stream margins, feeding on small invertebrates. Adults have quick, darting flight and tend to approach from above and behind a moving target.

Deer flies undergo complete metamorphosis. Eggs are laid in masses on vegetation overhanging water, and larvae drop into mud or shallow water to develop over several months, molting repeatedly while preying on small organisms. Pupation occurs in nearby moist soil, with most species completing one generation per year and overwintering as larvae.