Marsh flies swarm your beach day? File a greenhead report.

A unique kind of beast emerges from the marshlands of the East Coast each July. 

New England beachgoers know them well: With bulging, Kelly green eyes, and mouthparts that slice into their targets’ skin like scissors, greenhead horseflies can’t be ignored. 

But with enough data, they can, perhaps, be avoided — at least, that’s what web developer turned volunteer insect data collector Greggory Hogan hopes. 

On Hogan’s website, The Greenhead Report, users track and compile data on the insect that disrupts beach days and the East’s coastal economy every July and August.

At first, Hogan hoped the site — one of many “side projects” — would inform his own beachgoing habits. He often bicycles to the beach, he said, from his home in Newburyport, Mass.; if a swarming cloud of green-eyed flies is waiting for him there, he’d prefer to skip the trip. 

So, to help himself and other prospective beachgoers gauge the midsummer fly situation, Hogan developed a two-step online form. Reports roll in from the perhaps-unlucky individuals already on the sand.

The first question is a simple one: “Have you seen a greenhead today?” Then, if the answer is “yes,” users rate the amount of flies they are contending with on a four-part scale, from “not bad at all” to “HOLY CRAP.”

Reports cover a string of beaches from Massachusetts to Maine, including New Hampshire’s Hampton Beach.

Hogan has never advertised the site, he said. Yet curious New England internet users seem to have discovered it themselves. As of late July, about 500 people had submitted a report so far this year. Thousands more had visited the site for a fly forecast. 

When people come together to log nature observations, the data stacks up, said David Angelini, an entomologist and biology professor at Colby College in Waterville, Maine. It’s exciting, he said, when community science projects “snowball” and grow.

Projects that encourage people to participate in observing nature “can kind of open up that world, of being exposed to all the living world,” said Angelini, who runs his own citizen science project compiling observations of another small, winged creature: the soapberry bug.

“There’s always going to be value to increasing public awareness about something like a greenhead — a part of the natural world that impacts us,” he said.

Community science data is inherently limited by the way it tends to “accumulate” naturally as people happen to make and record observations, Angelini said. “If you were an ecologist and you set out to study the distribution of organisms, it’s not how you would approach it,” he said.

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That’s one reason Hogan is hesitant to call himself a scientist.

“I don’t think I’ve ever tried to frame myself or, like, thought about it in that way,” he said.

Yet, Angelini added, despite some limitations, observations generated by projects like Hogan’s “can still be useful and valuable information.”

“Time and resources are limited in terms of people who are practicing scientists. To get the public involved is a real help, honestly,” Angelini said. 

And indeed, Hogan’s work seems to be one of relatively few endeavors currently collecting population-level data on greenheads in New Hampshire and nearby marshes.

Previous projects have looked at the yields from greenhead traps — boxes placed in coastal marshes and primed with fly bait — to study the flies’ population health, according to Amelia Taggart, a technician with Rye’s Seacoast Science Center. But these days, Taggart said, the boxes are “primarily” used to reduce the flies’ populations in an attempt to lessen the amount of painful bites received by beachgoers.

Greenheads are a useful insect to study, in part because their populations’ health is understood to mirror that of the estuarine ecosystem as a whole, Taggart said. The flies also play an important ecological role, feeding on (and being fed on) by many other marsh residents. The insects provide a food source for seabirds like sandpipers and willets. 

Hogan hopes to refine his website to make it more professionally useful to scientists. He’s thinking, for example, of incorporating more charts and other data visualizations, and possibly tweaking the form — though, he said, “I still want it to be fun.”

He is also planning some analysis of his own. For instance, Hogan wants to fact-check the local legend that greenheads emerge and fade away with the full moon. To do so, he will cross-reference data from the project, which has run since 2020, with moon and tide charts. 

Angelini said the data could already be useful to researchers, but could be refined further — for instance, by allowing users to record the location where they made their observation, or simply adding more sites to the list. He also suggested working with iNaturalist, a massive online collection of observations that Angelini sees as the gold standard for citizen science data.

Though greenheads can be a nuisance in the summer, we and the ecosystems they call home would likely be worse off without them, Angelini said. And, besides, they are a unique insect to behold.

“Honestly, I mean, they are kind of beautiful,” he said, “if they weren’t so painful.”