‘Head to the hills’ is what I want the huge ferocious flies to do.

And it wouldn’t be difficult for them to fly far away, considering their large size and strong wings that allow them to travel for miles.

Greenheads are here and are already horrendous. How else could you describe an insect that so diligently disrupts even the best day at the beach?

Don’t blame the boys. It is only the ladies that make you lament. Female greenhead flies start out innocently enough, though. In fact, they first feast harmlessly on nectar, plant honeydew and other vegetative carbohydrates. 

Then their maternal instinct kicks in. Female adult greenhead flies lay their first 200-egg mass without tasting a single drop of blood.  But that mass will be her last if she doesn’t go for blood. For every blood meal she takes in, she can lay another large egg mass. So for her fertility and genetic survival, more blood equals more offspring. You almost can’t blame her hunger, though you can hope she slurps from someone else.

Anyone that has been bitten knows the blame is all hers and has little sympathy for these suckers. Greenhead female flies use a scissor-like two-part jaw to saw into human or mammal skin, breaking many capillaries at once so the blood pours out. Her saliva includes an anticoagulant so that the blood will continue to flow and she can continue to consume it.

July is the peak time when these flying monsters are at their worst, though their terroristic reign can continue through the end of summer.  Greenheads breed and develop in salt marshes, right next to some of our favorite beaches.

Don’t expect the piercing pain to desist anytime soon. Greenheads can live up to four weeks and don’t stop the biting. Warm sunny days with little wind are the best for these bugs and they seem immune to any sort of bug repellent, perhaps due to their size and strength.

But there is a good side even to these grating greenheads. Their larvae, which grow from eggs laid in the marsh muck, provide food for shorebirds and fish. And the big adults are a bountiful bite for aerial insectivores. Birds, such as swallows, swoop and dart around the marsh looking for greenheads to gobble.

There are some recommended strategies to avoid these fruitful flies. One tactic would be to cover up, since these flies can’t tear through cloth, but that usually isn’t the point of a day at the beach. Light color clothes are said to help, and those black boxes in the marsh will also prevent future attacks by trapping adult females.

It would be nice to be able to call in a swat team, but the flies’ numbers and agility make that approach ineffective. Especially irritating is the fact that just when one has begun to enjoy getting “far from the madding crowd,” a maddening crowd of these insects will surround you.

But as angry as they make you, and for all their power to drive you absolutely crazy, just be sure to remember the good advice that suggests not to “remove a fly from your friend’s (or your own) forehead with a hatchet.”

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