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.