Millions of Microscopic Fly Carcasses Left Dark Stains on People’s Feet at New England Beaches

The unusual event affected a 70-mile stretch of beaches from Massachusetts to Maine

A photograph shows Wells Beach in southern Maine with beach houses on the horizon
Samples gathered at Wells Beach, shown here, revealed that the mysterious brown substance was made up of millions of bug carcasses. Photo by Bud via Flickr under CC BY 2.0

Summer temperatures finally reached New England this week, and people were excited to hit the beach and walk barefoot in the sand. But some beachgoers were in for a surprise: dark-colored stains on the soles of their feet that wouldn’t come off no matter how hard they scrubbed. Beaches along the 70 miles from Wells, Maine, to Gloucester, Massachusetts, were affected by the mysterious muck, Heather Murphy reports for the New York Times.

It took a few days to get answers, and the reality might make your skin crawl: millions of microscopic, dead flies had washed into the sand. The dark color on people’s feet probably came from pigment that the insects acquire from their food, Eric Russel reports for the Portland Press Herald.

“It looks like I walked through the blueberry field barefoot,” says Alyssa Mewer, a resident of York, to Gabrielle Mannino and Dustin Wlodkowski at News Center Maine. Mewer’s sister’s feet turned black with a green shine, and her kids’ feet were tinted blue. And the color wouldn’t fade, even after multiple showers and heavy scrubbing.

"It’s kind of strange that it won't really come off very easily," Mewer adds to News Center Maine. "So more than anything, we're just curious."

Concerned beachgoers sent photographs of the black stains to the Maine Department of Environmental Protection (DEP) in search of answers. People were most concerned that it might be something dangerous; theories included algae and oil. Maine DEP officials disseminated the pictures to several experts in the hopes that one might recognize the substance.

“This is the first time I’ve seen or heard of this in my 35 years,” says Maine Geological Survey marine geologist Steve Dickson, who received photos from the DEP, to the Press Herald. “Normally this time of year we get calls about too much seaweed (wrack) on the beach and the swarming flies that hang around the decaying seaweed. This wasn’t that.”

Dickson recognized Wells Beach in the photos he received, so on Monday he contacted retired NOAA oceanographers Linda Stathopolos and John Lillibridge, who live in Wells. The pair, who are married, took a stroll on the beach to collect samples.

“We went walking, and saw all this goop on the beach,” says Lillibridge to Emily Sweeney at the Boston Globe. “Every wave would bring in more of this crud.”

The “crud” was dark brown in color and resembled slimy bits of seaweed or algae, Lillibridge says. They gathered samples to store in the fridge, and Stathopolos took a look at some of the substance under a microscope.

“There were tons and tons of little bugs, about the size of a tip of a pin,” says Stathopolos to the New York Times. “They were definitely all dead.”

“You can’t tell they’re bugs until they’re under a microscope,” says Lillibridge to the Boston Globe.

On Wednesday, Maine’s Department of Agriculture, Conservation and Forestry shared that the millions of dead bugs had been identified as black kelp flies, which eat decaying seaweed. When the flies eat seaweed, the pigment remains in their bodies until they die. When unsuspecting beachgoers walk across a patch of dead flies, the pigment transfers to their feet.

“It’s just a natural dye. Like getting berry stains on your fingers,” says Lillibridge to the Boston Globe, adding that the coloring is not dangerous and not permanent. And by late Wednesday, the beaches were cleaned—a high tide or a shift in the wind had washed the bug carcasses away.

Maine officials are still trying to determine where the flies came from, and why they washed ashore at once, but they do not expect it to become a regular occurrence.

“It’s not known why,” the bugs all washed ashore at once, said Maine Department of Agriculture spokesman Jim Britt to the New York Times. “Nature does crazy stuff. This might be one of those instances.”

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