Mystery substance staining beachgoers' feet in Maine identified as bugs

June 9 (UPI) -- An ocean researcher said the mysterious black substance that has been staining the feet of visitors to Maine beaches is actually the crushed remains of tiny insects.

The York County Parks and Recreation Department said on its website that Department of Environmental Protection officials were investigating after multiple visitors to southern Maine beaches reported the bottoms of their feet had been stained by a black substance that was difficult to wash off.

The substance was initially thought to be algae, but John Lillibridge, a recently retired oceanographer from the National Oceanic and Atmospheric Administration, examined a sample through a microscope and made a surprising discovery.

"Much to our surprise, it wasn't some kind of algae or an oil spill like you would expect, it was just a whole bunch of dead bugs in the water," Lillibridge told WMTW-TV.

Lilligridge said the insects have wings smaller than a pinpoint, but in such large numbers they cause dark stains when stepped on.

Steve Dickson, a marine geologist with Maine Geological Survey, confirmed Lilligridge's findings.

"This is the first time I've seen or heard of this in my 35 years," Dickson told the Portland Press-Herald. "Normally this time of year we get calls about too much seaweed on the beach and the swarming flies that hang around the decaying seaweed. This wasn't that."

Dickson said he is now working with entomologists to identify the insects and determine where they came from. He said he expects the bug debris to wash back out to sea when the winds change.