Midge infestation in Back River a mystery

Flying insects cloud the waterfront, harassing boaters and residents

July 03, 2010|By Timothy B. Wheeler, The Baltimore Sun

There's new life in Back River — though not quite what folks had been hoping for.

The eastern Baltimore County waterway, long degraded by sewage and development, has been humming the past few summers with hordes of midges, gnat-like insects that swarm over the water and along the shoreline.

They don't bite, though they look like mosquitoes. But their mating swarms are bedeviling waterfront residents, boaters and marina operators because the bugs are drawn to lights and light-colored objects. They get into people's hair, ears and eyes — and even occasionally get inhaled.

"It was insane," recalls Brian Schilpp, of a daytime infestation of Rocky Point during a recent fishing tournament. "It looked like locusts. … Every leaf of every tree was covered with these midges," and, he added, the wind was blowing them about "like confetti."

Besides their maddening swarms, their carcasses and waste wind up speckling boats, cars and trucks like sprayed-on pepper.

"It's very agitating … extremely bad, a nuisance to say the least," said Jeff Zahner, manager and co-owner of Weaver's Marina in Essex. He says he's lost customers because of the swarms. "I've been on the river all my life, and I haven't seen anything like it the last four years."

Why the recent explosion in midges on Back River, no one seems to know. Some species are found in waters fouled by nutrients from sewage and storm-water runoff, and the river has some of the poorest water quality in the Chesapeake Bay. Back River and its similarly degraded neighbor, the Patapsco River, earned a collective 'F' on the latest University of Maryland report card on the health of the bay and its tributaries.

Back River is the receiving water for one of the state's largest sewage treatment plants, which processes 180 million gallons of wastewater daily from 1.3 million city and county residents. Some also have speculated that sediment flushed into the river from highway work or other construction in the 55-square-mile watershed has driven away fish that might eat the bugs.

Those are all possibilities, one expert says. But it may also be that the plague of midges reflects some improvement in the river's condition, says Susan Gresens, associate professor of biological sciences at Towson University.

Gresens has studied midges elsewhere and has been called on to help the county solve the mystery of the Back River midge invasion. She said she knows of at least two cases where midge infestations cropped up as polluted, lifeless lakes were cleaned up. So it could be, she said, that "yeah, life is coming back to Back River, but it's a little more than we wanted."

Whatever the case, Baltimore County has launched an investigation to get to the bottom — literally — of the phenomenon.

This week, Kevin Brittingham and Dennis Genito, a pair of county natural resources specialists, motored out from Weaver's Marina in an outboard-powered skiff to look for midge larvae on the river bottom.

A great blue heron flew overhead, and a tern scooted away as the boat cruised past the Back River sewage treatment plant and an old landfill to a spot between two busy highway bridges. Piles of tires poked out of the shallow water — assembled in advance of a big river trash cleanup planned next weekend.

There, wielding a long-handled Ekman hand dredge, Brittingham scooped up a six-inch square of bottom muck mixed with blackened leaves. He rinsed the grayish silt out in a bucket strainer and had no trouble spotting the tiny midge larvae left behind, bright red and maybe half an inch long.

"People call them bloodworms, sausage worms," Brittingham explained as one wriggled on his fingertip. "Every sample we take, we find them."

Since beginning their sampling last fall, Brittingham says they've found from 600 to 6,000 midge larvae per square meter on the river bottom, with an average of 1,500 per meter.

In that larval stage, newly hatched midges feed on algae or other organic matter on the bottom, until they morph into pupae that swim around near the water's surface. Finally, they morph again, sprouting wings and going airborne, to swarm in clouds at night and look for mates. The females then lay their eggs on the water, to start the cycle of life anew. All of this takes just a few weeks.

"I call them the rabbits of the aquatic world," said Gresens. "They reproduce like mad, and everybody eats them."

Normally, the swarms wouldn't be that bad, because midges in their water-borne stages are a favorite food of fish and other aquatic creatures. But those biological controls aren't working right now in Back River.

"Maybe the habitat has been changed so that certain kinds of midges survive better," Gresens said. "Maybe some of it has to do with changes in fish populations."

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