Shoo fly, don’t bother me.

Salt marsh greenhead flies have arrived. Or rather, they have emerged, since they have been hanging out in the salt marsh over the last year, in densities that may surpriseyou. This year, they are both early and prolific, and (as always) they are out forblood. 

Your blood would be perfect, as would the blood of your pets, livestock or other wild animals. This draculian drink will provide a necessary protein boost for the female fly. She simply could not do without it, if she is to successfully raise more than one brood of young.  

Consider her not only a bloodsucker, but a carnivore and a cannibal. In the early lives of female greenhead flies, shortly after they have emerged from their mud-bound pupas, they consume worms, insects, snails, other invertebrates and even their own kind, crunching and munching on the larvae of other greenheads. These delicacies would be her first course.

The second course for her feast is blood. Both meals are replete with protein needed to produce her egg masses.

She can lay eggs multiple times, depositing groups of 100 to 200 on the grasses of coastal salt marshes, the greenhead’s home turf. When the eggs hatch, the larvae drop or burrow into the rich, mucky marshsoils. A square yard of salt marsh soils can harbor more than 70 greenheadlarvae! 

Eggs can hatch within a few months, or they can overwinter in a pupal stage. Herein lies the rub. 

The greenheads that we are seeing now may be the result of both last year’s brood and this year’s. Last July was very wet, so the greenheads did notemerge. They hunkered down and waited another year to comeout. Thus, we are getting a double dose, twice as many greenheads as we would in a normalyear. Dry weather is good for them, and this year has been nothing if not dry.

Things may get worse in the salt marsh and beyond, since traditionally the third week of July is when they are most vicious. Once they hatch, they travel upland to hunt, using their namesake large green eyes to find theirprey. Greenheads can live for up to a month before they get too weak tobite. Only wind will limit their flyingability. Most insect repellents won’t dissuade them either, although viscous and gooey varieties will help thwart their biting. 

A bite from a greenhead is quite painful, arguably worse than your average mosquito. Mosquitoes inject a needle-like proboscis into your skin, while a greenhead has a two-part mouth that allows it to slice and gouge skin in order to promote the pooling of blood for them todrink. 

Anyone who has encountered these fierce flies will feel certain that greenheads must have been the species of fly that was sent to plague Egypt in the biblical story.

Their unrelenting attacks definitely qualify them as a scourge, so my best advice is to find somewhere else to be when they are around, pray for a strong wind, or prepare to fight the losing battle against their constant nips and bites.

Outranking even the hated mosquito as the most obnoxious insect of summer is no small feat, so perhaps greenheads deserve some credit at least for that distinction. They will win praise for nothing else from me.

Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown.