Greenhead flies are a type of biting insect belonging to the horsefly family, Tabanidae. These insects are recognized by their large, iridescent compound eyes, which often appear as a striking dark green. Found predominantly in coastal regions, greenheads are a common summertime nuisance.
The Biological Imperative to Bite
Only female greenhead flies bite, and their biting behavior serves a specific biological purpose. Female greenheads require a blood meal to obtain the protein necessary for the development and maturation of their eggs. This protein need is common among many biting insect species. After laying an initial egg mass, a female fly must then seek a blood source to produce subsequent batches of eggs, often laying 100 to 200 eggs per blood meal. Their bites are notably painful because greenheads possess scissor-like mouthparts that cut the skin to create a wound, from which they then consume the pooling blood.
Greenhead Habitats and Peak Activity
Greenhead flies are commonly found in coastal marshlands, salt marshes, and wetlands along the Eastern United States. Their entire life cycle, from egg to adult, takes place within these moist, muddy environments. These insects are most active during the summer months, with peak populations from late June through August. Highest densities occur in the last two weeks of July and the first week of August.
Female greenheads are most active during daylight hours, from 10:00 AM until dusk. Their activity intensifies on hot, humid days, which often coincides with peak recreational use of beaches and coastal areas. These flies are attracted to movement, carbon dioxide, and dark objects, which helps them locate hosts for a blood meal.
Strategies for Bite Prevention
Wearing protective clothing, such as long-sleeved shirts and pants, can create a physical barrier against their bites, as they cannot bite through fabric. Opting for light-colored apparel is also advisable, since greenhead flies are attracted to dark objects.
Using insect repellents containing active ingredients like DEET, picaridin, or IR3535 can offer protection. Some natural repellents, including those with cedar oil or natural black pepper extract, are also available. Avoiding known greenhead habitats during their peak activity times, especially on hot, sunny days, can significantly reduce exposure. Drying off immediately after being in water also helps, as sweat and saltwater can attract these flies.