Ogunquit Beach from Marginal Way in Ogunquit, Maine on July 16, 2015. File photo.
Rick Friedman/Corbis via Getty Images
  • People complained about their feet turning black after visiting Maine beaches this week.
  • Maine officials believe millions of dead kelp flies are the cause.
  • They say the flies died on the beaches, their carcasses leaving pigmentation on people's feet.
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Millions of tiny black kelp flies are staining people's feet black on beaches in Maine and New Hampshire in the US.

Dozens of people in Maine and New Hampshire complained to officials and on social media about the soles of their feet turning black after visiting local beaches, and for days, no one could figure out the cause.

But Jim Britt, a spokesman for Maine's Department of Agriculture, Conservation and Forestry, told the New York Times that the likely cause is dead flies.

He said millions of tiny black kelp flies have apparently died on a stretch of beach in southern Maine. One area that was particularly impacted was Wells Beach, The Portland Press Herald reported earlier this week.

"It's not known why," Britt told The Times. "Nature does crazy stuff. This might be one of those instances."

Steve Dickson, a marine geologist with Maine Geological Survey, told the Press Herald that the kelp flies eat plants that contain naturally occurring pigment, which can transfer to a person's skin if they come in contact with it.

"This is the first time I've seen or heard of this in my 35 years," Dickson said.

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