The greenhead bug, also known as the greenhead horse fly, is a common presence in coastal regions. These insects are a nuisance during warmer months, especially in salt marshes along the Atlantic Coast from Nova Scotia to Florida. Their persistent biting behavior impacts outdoor activities and can affect local tourism.
Identifying the Greenhead Bug
The greenhead bug belongs to the horse fly family, Tabanidae, specifically Tabanus nigrovittatus. These stout flies are smaller than many other horse fly species, often similar in size to a common housefly, reaching about half an inch in length. A distinguishing feature is their large, iridescent compound eyes, which display a striking dark green color.
Their bodies are generally light brown, and they possess a flat head. Male greenhead bugs have eyes that touch at the front of their head, while females, which are the ones that bite, have a noticeable separation between their eyes. Unlike some other horse flies, Tabanus nigrovittatus lacks dark markings on its wings.
Habitat and Behavior
Greenhead bugs primarily inhabit salt marshes, coastal areas, and wetlands, environments crucial for their life cycle. Female greenhead flies lay their eggs in clusters on marsh grass or other vegetation near water. After hatching, the worm-like larvae burrow into the marsh mud, where they can live for one to two years, preying on other small invertebrates.
Adult greenhead flies typically emerge in late spring, with peak activity occurring from early July through August. They are most active during daylight hours, particularly on warm, sunny, and calm days. Female greenhead flies require a blood meal for egg development, producing 100 to 200 eggs per batch. Their mouthparts are equipped with scissor-like structures that slice the skin to access blood vessels, resulting in an immediate and painful bite that feels more like a cut. They also inject an anticoagulant saliva to ensure blood flow, which can cause pain and swelling.
Managing Greenhead Encounters
Avoiding peak activity times, generally from 10:00 AM to dusk, and locations like dense marsh areas can reduce encounters. Greenhead flies are less active in windy conditions, so choosing a breezy spot can offer some relief. Wearing appropriate clothing provides a physical barrier against bites.
Light-colored clothing is recommended, as biting flies tend to prefer dark objects. Long-sleeved shirts and pants can prevent bites since the insects cannot bite through fabric. Commercial repellents containing DEET or picaridin may offer limited protection, but are not always highly effective. If bitten, cleaning the site with soap and water can help prevent infection. Applying ice can reduce swelling and numb the pain, and over-the-counter antihistamines or hydrocortisone creams may soothe itching and inflammation. If a bite becomes excessively red, warm, or swollen, or if symptoms worsen after a few days, medical attention should be sought.