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Greenhead Flies | What are Greenheads?

But above and beyond these physical characteristics, and the fact that greenhead flies will indiscriminately attack horses, cows, dogs, hogs, and deer, this fly is notorious mainly for one thing: the pain it inflicts in large numbers on beachgoers at the height of summer. Make that two things, because like The Terminator, this fly is relentless. It will not stop until someone pays the price.

Stories of encounters with greenheads have a dramatic quality usually reserved for plays written by one-name ancient Greeks. But the blunt truth is that these creatures can ruin a day, or days, at the beach.

Often during peak greenhead season–generally early or mid-July to mid-August–beaches will post warnings about fly conditions, like some weird variation on the surf report. At Crane Beach there’s another sign, too: No Refunds. But it’s not about singling out one beach or another; any gathering spot near a salt marsh–beach, restaurant, or home–is potentially vulnerable. Sometimes it’s just a matter of degree.

“All salt marshes on Cape Cod provide habitat for greenhead flies,” says Gabrielle Sakolsky, entomologist and assistant superintendent at the Cape Cod Mosquito Control Project. “Our largest marshes, adjacent to the large barrier beaches of Sandy Neck and Nauset, are the worst, because they have the largest amount of larval habitat. There are no immune spots.”

If that’s the case, I suddenly have more questions. Can greenheads be outsmarted? What makes them so rabid in the first place? Why is the pain so fierce? And don’t we have any options?

In search of answers, I’ve found myself knee-deep in a salt marsh with John Stoffolano, Ph.D., professor of entomology at UMass Amherst. It’s early August: prime tabanid time.

Greenheads | What are greenhead flies?
Photo/Art by Annie Graves
Entomologist and UMass Amherst professor John Stoffolano prepares to study greenhead flies near his campus office.

Every summer, Dr. Stoffolano and his students head into the dark heart of greenhead territory–the broad and glorious salt marshes that spread out around Pine Island, in Newbury, Massachusetts, not far from Crane Beach. Here they collect thousands of flies from the shiny black wooden boxes that stagger on slender legs across the marsh, like dark, square animals imagined by a Cubist carpenter. Back at UMass, they conduct research on greenhead behavior and physiology. “We’re the only ones doing this kind of work,” Dr. Stoffolano told me when I first visited his office in Amherst, months earlier. “At one time there was a lot of interest.”

Greenheads | What are greenhead flies?
Photo/Art by Annie Graves
John and Susan Stoffolano heading to the traps set for greenhead flies.
Greenheads | What are greenhead flies?
Photo/Art by Annie Graves
John and Susan Stoffolano collecting greenhead flies.

That was before scientists learned that tabanids do not in fact carry Lyme disease or AIDS, that they’re merely a horrible nuisance. But in the 30-plus years he’s been researching these greenhead flies, Dr. Stoffolano has learned a lot, and he’s got the office to prove it. Bookshelves overflow with the chaos of his profession–research materials, scientific papers (many his own), and reference books–the contents spilling onto the floor, the desktop, any available surface.

In sharp contrast to its occupant, who is neat, self-contained, and, it turns out, pretty funny, with an adventurous streak. Tales of tsetse flies in South Africa, encounters with biting beach flies in the Seychelles, and experiences at a Zulu healing ceremony weave in and around talk of greenhead flies. His mother is part Mohawk Indian, and Dr. Stoffolano’s interest in indigenous cultures and insects has gradually evolved into a college course on cultural entomology, in which he uses insects to teach diversity, while incorporating references to art, music, mythology, and archaeology. Traces of Indiana Jones, minus the bullwhip.

Over the next few hours, I get a crash course in greenhead flies: Tabanids 101, if you will. For instance, I learn that the males don’t bite. Only the female is out for blood, but when she first takes flight, she’s actually a vegetarian. It’s a little like hearing that sharks prefer salad. (The seeds of bloodlust are sown early, though; the larvae are carnivorous and cannibalistic, and if there’s nothing else handy, like an earthworm or some other type of larva, they’ll eat each other.)

Greenheads | What are greenhead flies?
Photo/Art by Annie Graves
John Stoffolano transferring greenhead flies for research

“Before she’s laid her eggs, you can even let her take a walk on you,” Dr. Stoffolano insists. “When the males and females emerge from the pupa stage, they feed on carbohydrates, like nectar or honeydew, for energy, for flight. That’s their gasoline. But once the female lays her eggs, her whole behavior changes. She becomes extremely aggressive. In this second cycle she’s seeking a host–cow, deer, human. She needs to have a blood meal if she’s going to lay another batch of eggs.”

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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18 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.

    • Chris Powers July 18, 2016 at 1:24 pm #

      On a boat off of Plum Island we resorted to electric fly swatters!

  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.

    • Christine Allen July 18, 2016 at 1:27 pm #

      Laura, what you are saying about the wind is so correct.We lived in Delawae-Rhoboth Beach- and like to surf fish, but did watch the wind report right before we left the house. We were also bothered by the small black flies that also bit- horrendous

  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.

    • Bill Hogan July 16, 2016 at 2:19 pm #

      No, they were onPine Island. It’s near Plum Island but a different place.

  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.

  8. Renate Kovacs July 5, 2016 at 11:03 pm #

    Greenheads aren’t so bad. Think of the birds who feast on them. Also the greenheads move slowly, so you can slap them before they bite you. If you have a lot of greenheads you have a healthy salt marsh. I used to work on Plum Island. We wore Skin So Soft Bathoil, by Avon. You have to put it on several times a day, but it works. They won’t bite if you have it on.

  9. Rbd July 19, 2016 at 2:37 am #

    How do you sooth the bites afterwards? My legs and ankles still hurt from the bites I received this weekend on the Connecticut shore.

  10. BBSteve July 19, 2016 at 10:11 am #

    Covering bare skin is the only thing that stops greenheads from feasting on human flesh – Avon planted the Skin-so-soft remedy to boost sales, just salad dressing for greenies, better for soothing than repelling (no such thing as repellant – only hides you from odor tto stave off greenhead attraction) – we always used the last full moon in August to wish them good-bye for the season…time to check moon chart…

  11. Kat Sullivan July 19, 2016 at 10:33 am #

    My Aunt Mimi lived on Greenpoint way in Ipswich, literally in a sea hay barn, as a young girl I spent many summers there. I became so use to them, swimming in the marshland, but I have many battle wounds, but I wouldn’t change one thing about it. Awesome article, thanks for writing it.

  12. Joe E July 21, 2016 at 10:56 pm #

    I grew up in Salisbury, Mass. My father was an avid boatsman, and a boat builder. And I was taught that greenhead flies start emerging at the full moon of July, and subsides at the full moon of August, they peak at midway through their cycle.

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