WELLS, Maine (AP) — Scientists have determined that a black substance that had settled near the shoreline over several days at a beach in Maine is made up of millions of dead bugs.

One of the regulars who walk Wells Beach, Ed Smith, took photos of the substance in the sand and sent them to the state Department of Environmental Protection, the Portland Press Herald reported Tuesday.

Smith wanted to know because he said his feet were dyed black after walking through it and he wanted to know if it was possibly toxic.

Steve Dickson, a marine geologist with Maine Geological Survey, figured out what was going on with the help of two retired oceanographers who live nearby. One of them, Linda Stathoplos, took a sample from the beach and looked at it under her microscope.

“It was clearly little bugs,” Stathoplos said.

Dickson said millions of bugs floating in the ocean settle on the beach when waves wash ashore, and they remain there when the tide goes back out.

“This is the first time I’ve seen or heard of this in my 35 years,” Dickson said, adding that he is still trying to determine what the bugs are, where they came from and why. But he does not expect it to be a regular occurrence.