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Greenhead Flies | What are Greenheads?

Then he shows me the photos. And now I understand why it hurts.

Unlike the delicate mosquito, which is a vessel or capillary feeder, drawing blood much like a syringe does, tabanids are pool feeders, meaning they sever lots of capillaries at once, in order to create a gaping wound so that the blood can pour out. Close-ups of the greenhead’s tiny mandibles reveal an unsettling similarity to a pair of deadly, razor-sharp scissors, able to slice through skin like a knife through mayo. Tiny temperature receptors on the insect’s antennae have already detected whether or not the host is warm-blooded. Now that she’s attached, two other mouthparts pull her head deeper and deeper. She’ll keep on sucking until you smack her away. Then she’ll come back for more. Over and over and over.

At first, according to Dr. Stoffolano, it doesn’t hurt. “I’ve watched them go all the way down into my hand,” he says matter-of-factly. “They probe the skin for temperature, then they pierce the skin, and then they salivate. The saliva contains an anticoagulant so that the blood doesn’t clot. As soon as they release saliva, which is a foreign protein, our bodies react to it and we sense pain. That’s when we swat ’em.”

Pain is the greenhead’s great enemy. The very thing she does so well keeps her forever hungry: The viciousness of her bite practically guarantees that it will be difficult for this insect to get a good meal. But here’s where Nature’s brilliant adaptability comes through, letting the greenhead make the best of a bad deal.

“There’s not a lot of blood out on the salt marsh,” Dr. Stoffolano says. “They probably never get a good blood meal. So they’ve evolved a strategy of being able to lay the first egg batch without taking a blood meal. And that’s one of the major problems in controlling this fly. You’ve seen all the traps, right?” I nod my head. Anyone who’s driven the East Coast during the summer months can’t miss the black boxes strewn about the salt marshes up and down the Atlantic. “All those females that go into the traps have already laid a batch of eggs first. So you’re not cutting down on the population. What you’re cutting down on is the biting frequency and the nuisance factor. The traps are nuisance control.”

Which is still better than nothing, he acknowledges. Greenhead adults live three to four weeks, so the population builds up. They’re strong fliers, too, so if they can’t find a meal at the beach, they’ll fly a couple of miles inland. And although on a good day a greenhead can lay up to 200 eggs in what may be her first and last reproductive act, these dark, heavy traps–painted black to mimic large animals, like cows–can attract and capture up to 1,000 greenheads per hour. That’s good news for beachgoers, boaters, and anyone who lives nearby.

Frankly, short of spraying the entire East Coast, there aren’t a lot of other options. The insects themselves are too big to eliminate without using massive amounts of pesticides, which would damage the delicate salt-marsh habitat. Besides, greenhead flies play a couple of important roles within that fragile ecosystem. First, as an indicator of marsh health. And second, as a food source: Their spring larvae are consumed by shorebirds and fish, while adult greenhead flies are protein for purple martins and tree swallows. Eat or be eaten.

“The other problem we face with these greenheads is the vastness of the salt marsh,” Dr. Stoffolano adds. “It goes from Texas all the way around Florida, all the way up the East Coast, up into Nova Scotia. It’s a huge area. How do you control such a vast area?”

Meanwhile, I’m about to visit my first trap. I’m wading through thigh-high grass with Dr. Stoffolano and his wife, Susan, headed toward one of the greenhead traps alongside the road that cuts through the marsh around Pine Island. I’m wearing light-colored clothing, because greenhead flies zero in on dark, moving objects, and I’m covered head to toe, despite the blazing heat. We approach the first black box–it’s buzzing audibly.

“That’s a sound you don’t want to hear,” Susan Stoffolano observes, as we peer through the thick screen on the top of the box, reinforced so that birds can’t tear it apart to get at the insects. Inside, the box is crawling with tabanids, and two interior troughs are littered with corpses. There’s no bait; the insects enter from below, fly up to the light, and then can’t figure out how to exit. (The Northeast Massachusetts Mosquito Control & Wetlands Management District installs and maintains the boxes, but lets Dr. Stoffolano remove greenhead flies as needed.)

Together, he and his wife unscrew a corner of the trap, drape towels over sections to direct the flow of insects, and position a mesh carrier over the opening. Low-tech, but it works. It quickly fills with live flies, and we move on to the next trap. A steady breeze blows, keeping us mostly fly free.

Listening to all this buzz reminds me of a story Dr. Stoffolano told me about how horses were once used on the marsh around Pine Island to help cut salt-marsh hay, which even today is prized by gardeners for inhibiting weeds: “They made nets out of ropes that completely covered the horse, so that as the horse moved, it would dislodge any tabanids that were trying to bite.” And even in modern times, rumor has it that sometimes the postmen around Newbury and Pine Island will balk at delivering the mail, because greenhead flies are attracted to the moving mail truck and get trapped inside with its unlucky driver.

So what’s a human to do? I ask the horsefly expert for any words of wisdom, recommendations, last-minute thoughts.

“If it’s the season of the fly in your area, you gotta wear light-colored, protective clothing,” he replies. “They can’t bite through your clothes. And I would suggest that more beaches post Web sites. If it’s a heavy day for greenheads, don’t show up at the beach; you’re wasting your money. Forget about it. If you’re a restaurant, and you don’t want people sitting outside to be bitten, then you put traps up.”

His hand flashes before me, and with a graceful swipe he captures a renegade greenhead, crawling on top of the trap. “They’re beautiful creatures, aren’t they?” he smiles. He’s gripping the insect in a sort of tiny Heimlich maneuver, so that it can’t bite him, and then he holds it up to my face for a closer look. I’m staring into a pair of huge (relatively speaking) green eyes. “Look at those eyes,” he marvels, and then releases it.

Please Note: This information was accurate at the time of publication. When planning a trip, please confirm details by directly contacting any company or establishment you intend to visit.

Annie Graves


Annie Graves


Annie Graves is a regular contributor to Yankee. A New Hampshire native, she has been a writer and editor for over 25 years, while composing music and writing young adult novels. Find out more about Annie at
Updated Monday, July 15th, 2013

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10 Responses to Greenhead Flies | What are Greenheads?

  1. Kathy Woinson July 12, 2014 at 12:58 pm #

    Great article I just read as I had to retreat to indoors because of how vicious the greenheads are today. I thought that they arrived on the new moon the end of June & were gone by the full moon high tide in July, which is tonight! Guess maybe that’s not true, maybe it’s the full moon in August?? Sure is a miserable few weeks and they certainly are nasty bighters!! Very informative article though,

    • Arvo August 1, 2015 at 11:26 pm #

      Greenies are in season from the first full moon in July through the next full moon. This is an odd case wherein the Hebrew calendar, based on lunar cycles, always works — with greenhead season starting out on the 15th of the month of Tammuz and ending on the 15th of Av. If it is extremely hot weather I have seen them come out a few days early, but by that second full moon — 15th of Av — they are all done.

  2. Helen Rankin August 4, 2014 at 8:41 am #

    I go to Cape Cod and some days green flies make it unbearable on Nauset Beach. Then we have Plovers nesting resulting in the closure of the beaches. It’s maddening!!

    • Michelle August 6, 2014 at 11:29 am #

      Hi Helen… Do you know if the green heads are still bad right now? Michelle :)

  3. Laura F. August 26, 2014 at 11:29 pm #

    I live in South Jersey and the only thing that works for me 100% no greenheads is…when the wind blows from the East (off the ocean). This keeps them at bay, literally. Lol
    The absolute worst time to go to the beach between June-September is when the wind blows from the West (off the land).
    I believe you’ll be fine with little to no flys if it blows from other directions too. IF the wind changes from the West while your there, a few flys MAY appear but leave right when it changes again.
    Since I live close enough to the beach to drive down for a day trip, I just check my Weather App the day before and morning of to see which direction the wind is blowing. I guess for those of you who go to the beach for more than one day on vacation, this method won’t help you that much.
    In that case, I’ve heard from many people that Avon’s Skin So Soft works as a repellent…I think they even have a bug repellent that’s water resistant with SPF 30, and anti-itch relief.

  4. Elizabeth June 23, 2015 at 8:39 pm #

    Just read the article. I hate these flies more than anything! They ruin our summers here in Newbury, Ma. The island referenced above is not Pine Island, but Plum Island. The greenheads near our home are horrible, and they have started early this year. We usually don’t see them for another couple weeks. :(

    • Big Yaz September 21, 2015 at 9:34 pm #

      It’s Pine Island. Follow Pine Island Road off Route 1A.

  5. Mary Beth July 12, 2015 at 11:57 am #

    Another reason to get a pool.

  6. Rebecca Jay July 15, 2015 at 1:32 pm #

    Spectacular article!!
    I’ve never heard of greenheads.. Read about them in a book & googled it.
    I found this article there. At first, I was tempted to move on because I was just looking for more info on them..habitat, photos, etc.
    However, this article was so well written I had to keep reading..all 4pages!
    Nicely done, Ms. Annie Graves!!

  7. Kerry murphy July 22, 2015 at 2:33 pm #

    Living right next to a salt marsh with a pool,we are not able to use the pool the last two weeks in July each year due to these mini monsters. We actually go to the beach because they aren’t bad there. I wish these researchers could invent a safe repellent that works.

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