Greenheads are a biting fly affecting outdoor activities in coastal regions. They are a seasonal nuisance, known for persistent biting. Understanding their characteristics, habitats, and impact helps minimize encounters.
Identifying Greenheads
Greenhead flies belong to the Tabanidae family, also known as horse flies, and include species like Tabanus nigrovittatus and Tabanus conterminous. They have distinctive physical traits, most notably large, iridescent compound eyes that often appear green, giving them their common name.
They are generally smaller than other horse fly species, measuring around half an inch (10mm) in length, with a flat head and a light brown body. Males have eyes that meet in the middle, while females’ eyes are noticeably separated. Their fast, agile flight and wings with characteristic ‘Y’ shaped veins at the tip are also distinguishing features.
Their Natural World
Greenhead flies thrive in coastal marshes, wetlands, and salt marshes along the Atlantic Coast, from Nova Scotia to Florida. Their life cycle is intimately connected to these aquatic habitats. Females lay egg masses, typically 100 to 200 eggs, on marsh grass, such as Spartina species.
After hatching, larvae burrow into marsh mud, living for one to two years and feeding on other invertebrates. They then transform into pupae in early summer or spring, and adults emerge.
Adult greenhead populations are most abundant from late June through August, peaking in late July to early August. They are primarily diurnal, active from 10:00 AM to dusk, especially during the hottest parts of the day. Strong westerly or southerly land breezes can exacerbate their presence, carrying them from marshes to beach areas.
The Impact of Greenheads
Greenhead flies are notorious for their biting behavior, exclusively carried out by females. Females require blood meals for protein to produce egg masses, with each meal supporting 100 to 200 eggs. Unlike many other biting insects, greenheads use scissor-like mouthparts to cut the skin, rather than piercing it. This creates a painful wound, leading to blood pooling that the fly then consumes.
Their saliva contains an anticoagulant, preventing blood from clotting. This causes characteristic symptoms: immediate sharp pain, followed by an itchy, raised, red welt. While most experience common reactions, some may develop more pronounced responses like larger, inflamed welts, blistering, or bruising.
Greenhead flies are not typically considered vectors for transmitting serious diseases to humans. However, bites can lead to secondary bacterial infections if the skin is broken from scratching. In rare instances, severe allergic reactions, including hives, extensive swelling, or difficulty breathing, may occur, requiring immediate medical attention.
Minimizing Encounters
Minimizing encounters involves several strategies to prevent bites. Wearing light-colored long-sleeved shirts and pants acts as a physical barrier, as these flies are attracted to dark objects. Avoiding outdoor activities during peak times (10:00 AM to dusk), especially in coastal or marshy areas, also reduces exposure. Drying off after swimming and avoiding perfumes or increased metabolic activity, which can attract them, may also help.
While DEET-based repellents are widely used, they are not always effective against greenhead flies. Picaridin-based repellents have shown better results. Securing homes and vehicles by keeping windows closed and repairing screens also prevents flies from entering.
If a greenhead bite occurs, prompt management can alleviate discomfort. Clean the affected area with soap and water to reduce infection risk. Apply a cold compress or ice pack to reduce swelling and pain. Over-the-counter antihistamines or anti-itch creams, like topical steroids, can manage itching. If symptoms worsen, show signs of infection, or indicate a severe allergic reaction, seek medical attention.