Baltimore County is bringing out the big fly swatter.

To combat the unprecedented numbers of swarming tiny flies known as midges that have invaded eastern Baltimore County’s waterfront neighborhoods this spring, the Baltimore County Department of Environmental Protection and Sustainability will double the area for its next helicopter treatment.

Instead of spraying 1,200 acres of Upper Back River with the specialized bacteria, the helicopter crew will also treat 2,400 acres of Lower Back River.

The helicopter will fly 90-foot wide passes across the river rather than the previous 45-foot passes, but will spray the same quantity of Bti, or Bacillus thuringiensis israelensis.

Baltimore County has been fighting midges for nearly two decades. The county and state stepped in with a $3 million eradication plan to spray a 1,200-acre section of the Back River.

But the latest infestation is a new problem and of a larger magnitude than previously thought. According to county officials, only two or three programs worldwide are treating midges at this scale. That means some trial and error as scientists collect data to determine what’s working — the system that worked so well in Back River may not work as well in the rest of Essex.

Residents of the Back River area had been complaining about the pesky flies for years when the problem finally seemed under control last summer. Then, suddenly, midges were bugging everyone along the waterfront in Essex. Some restaurants closed; others had to give patrons money back when the flies got into food.

At Jake’s Tavern, a popular Essex waterfront restaurant, owner Dave Jacobs said he had to remake several customers’ food last month because midges fell into their meals. One customer took Jacobs outside to show him his white pickup truck — it was completely covered with midges. No one was eating outside on the weekend before Memorial Day, despite the nice weather. Every time the door opened, he said, midges came inside.

“It’s ridiculous,” Jacobs said. “Horrible.”