The wood boring beetle, originally from China, has now been found in Anne Arundel and Allegany counties, and the bugs have become a costly problem.
"This wasn't unexpected, we maybe hoped it would be a little longer," says Carol Holko, program manager for plant protection at Maryland's Department of Agriculture. She says the bugs aren't just spreading on their own.
"It's being moved by campers, people who are moving infested firewood from other areas," she says.
Entomologists say the bug threatens to wipe out all the ash trees in North America. Mike Raupp is an entomologist at the University of Maryland.
"This is going to be enormously expensive," Raupp says. "We're talking about several million dollars or perhaps hundreds of millions of dollars to deal with this infestation once it hits a city like Baltimore."
The pest hasn't reached Baltimore, but if it does, the 300,000 ash trees in the city would have to be cut down as they die. The best way to prevent -- or, more realistically, delay -- this scenario is to avoid moving hardwood firewood under any circumstances, officials say.