salt marshes

salt marsh greenhead flies

If you’ve been to the east coast in the spring or summer months, you may know what I’m talking about. These monsters have huge green eyes, are very persistent, and bite like a vampire. Hint: check the weather and wind direction before your planned day at the beach. If the wind is out of the west for more than 24 hours, plan another day!

These vampires with wings are out for one thing YOUR BLOOD! Also known as the greenhead fly, the greenhead horse fly, the salt marsh green head. In more scientific terms, The salt marsh greenhead fly, Tabanus nigrovittatus, is an abundant and bothersome summertime pest along our coastal marshes. They were first classified by Justin Pierre a French Entomologist in 1847. Greenhead flies are produced from our coastal marshes of the Eastern United States. Developing larvae concentrate along the upper vegetational zone reached by daily high tides. The female greenhead's eggs are microscopic black dots and perpetuate the line of the host. When the flies are first born, they are actually vegetarians and feed primarily on nectar or honeydew, but once the female lays the first round of eggs, her entire behavior changes. Only the females bite and they do not discriminate between humans and animals as they seek a source of blood.


Adult flies mate on the open marsh. Within a few days and without seeking a blood meal, the female lays her first egg mass, consisting of 100 to 200 eggs. To produce additional egg masses, the female needs a blood meal. She becomes extremely aggressive. That is where you come into the picture. The female bites by lacerating the host’s skin with her mandibles after a sensor has determined the source to be warm-blooded. Once the host’s skin is lacerated, the female salivates into the wound releasing an anticoagulant so the blood doesn’t clot. It’s this saliva, which is a foreign protein recognized by our body, that causes the pain as an alert.

The greenheads are strong flyers. If they can’t find a meal in the marsh, they go out searching the surrounding areas ( beach, campground, golf course, horse farm, cattle farm or your back yard), they can fly for several miles inland until a good target is located. In a west wind, the greenheads fly across the bay to find your back yard, to feast on people or animals without discrimination. There is hope you can set-up traps – large black boxes that will reduce the greenhead population. These traps have been known to capture thousands greenhead flies.

Good news greenhead flies generally do not carry does not carry diseases. The Greenhead fly also plays an important role in the ecosystem as they are a food source for birds and fish.