Fun Facts

Greenheaded Flies 

Photo: https://vineyardgazette.com/news/2013/07/18/july-bites

In mid-July the female greenhead fly begins being an egg laying machine when she deposits her first 200 eggs in the salt marsh. The greenhead, which is in the horsefly family, has enormous green eyes laced with bands of iridescent red or purple. This fly has a voracious appetite and attacks horses, cows, pigs, dogs, deer and sunbathing people, but only the female bites. When the male and female emerge from the pupa stage they are vegetarians living on nectar, but the moment the female lays her first egg she becomes aggressive and needs a blood dinner to continue egg laying. Unlike the mosquito, a capillary feeder, greenheads are pool feeders, drawing blood like a syringe. Their tiny jaw bones have deadly, razor-sharp, scissor-like teeth that slice through the skin. The antennae detect whether the host is warm-blooded. As the skin breaks they release saliva containing an anticoagulant into the opening which allows the blood to flow freely and is then sucked up; it also triggers our reaction to the pain. The greenheads only live for three to four weeks.

All salt marshes on Cape Cod provide habitat for the greenheads, and the dark colored box traps you see in the marshes can capture up to 1,000 flies in an hour. Massive amounts of pesticides would be needed to eliminate flies, so the boxes do their job. The good things about greenheads are that they are an indicator of marsh health and they are a food source for shorebirds, purple martins, and tree swallows. 

(Source: https://en.wikipedia.org/wiki/Tabanus_nigrovittatus)