What is a Greenhead Fly?
The salt marsh horse fly, often called the greenhead fly, actually describes two species, Tabanus nigrovittatus and Tabanus conterminous. Both species of flies are found on salt marshes along the Atlantic Coast from Nova Scotia to Florida. On Cape Cod, adult flies are most abundant from July through mid-August.
The entire lifecycle takes place on and around the salt marsh. The eggs are laid on salt marsh grass (Spartina spp.). After hatching, larvae either crawl down, or get washed off the blade of grass. The larvae then burrow into the marsh and live there for 1-2 years. After that time the larvae come to the surface of the marsh to pupate.
Adult males and females feed on sugary substances (i.e. nectarlike) for energy. After laying their first set of eggs, females begin to look for a bloodmeal. Female greenhead flies require blood for their second set of eggs for the same reason that female mosquitoes need blood. The blood provides them with protein that is used to develop eggs. Unfortunately, female greenhead flies are present and searching for blood on beaches of Cape Cod at the same time that most visitors are using beaches for recreation.
How do the Greenhead Flies find you?
Female greenhead flies not only see you, but are attracted to you by your scent. They can smell the carbon dioxide and other chemicals that come out of you every time you exhale. This is also the way female mosquitoes find you. Haven’t you ever wondered how that one mosquito can find you when the lights are out and you are in bed?
What makes a Greenhead Fly bite hurt?
The greenhead fly, just like the female mosquito, injects her saliva into your blood when she first bites you. This saliva contains a chemical that keeps your blood from clotting or beginning to scab. The pain is your body’s reaction to this foreign chemical. The bump that proceeds the bite is caused by the continued allergic reaction your body has to the fly’s saliva.