People who've recently visited Wells Beach in Maine have often gone home to find their feet stained black—and scientists say they've figured out the gross reason. State officials say it's millions of dead bugs, washed ashore to form a black, slimy substance that resembles tar. Local Ed Smith first reported the odd ooze to the state Department of Environmental Protection this week, and marine geologist Steve Dickson, of the Maine Geological Survey, was one of the experts the DEP sent the pictures to, per the Portland Press Herald. Dickson, in turn, sent the evidence to Linda Stathoplos and John Lillibridge, a married couple who live near the beach and who happen to be retired oceanographers. They headed down to the shore, collected some samples, and stuck them under the microscope. "It was clearly little bugs," says Stathoplos.
Jim Britt of the state's Department of Agriculture, Conservation, and Forestry says the bug is probably "a harmless common kelp fly that feeds on decaying seaweed," per the Boston Globe. He adds that officials don't think the bugs cause any health problems if they come into contact with human skin. Lillibridge notes the hard-to-wash stain soon fades on its own, too. "Like henna dye, it wears away eventually," he says. "Like getting berry stains on your fingers." Some good news: The bug slicks—which the New York Times notes have also been reported on other Maine beaches, as well as in New Hampshire and Massachusetts—appear to have washed out to sea again at Wells Beach. But why did people's feet get stained in the first place? Dickson explains that bugs often chow down on pigment-heavy plants, filling their tiny bodies with those pigments. (Read more strange stuff stories.)