An adult emerald ash borer. Officials in Montgomery County’s parks department expect almost 3,000 trees will have to be removed this year after being infested by the beetle’s larvae. (Pennsylvania Department of Conservation and Natural Resources - Forestry )

Follow the woodpeckers.

That’s the mantra of horticulturists, arborists and nature lovers who monitor the health of ash trees. When the birds chisel away tree bark, it’s because they’re feasting on a green beetle’s larvae, and experts know it’s too late. The beetle, known as the emerald ash borer, has infested the tree and will eventually kill it.

“Unfortunately, they’re so hard to detect that often the woodpeckers find trees that are infested before we can,” said Patrick Harwood, a horticulturist for Montgomery County’s parks department as he inspected an infested ash tree along Rock Creek Trail in Kensington this month.

Ash-tree infestations are occurring at what arborists say is an alarming rate.

Last year, Harwood said, the county had to cut down about 80 infected trees. This year, county park officials expect that almost 3,000 will have to be removed, and they have already started.





The winter cutting targets the dead and extremely fragile trees that are the most likely to “fall and hurt someone,” Harwood said. About 1,800 need immediate attention, mostly along Rock Creek Trail.

Native to China, the emerald ash borer feasts on ash trees. And other than the woodpecker, it has no known natural predators in the United States.

[The emerald ash borer is one of the most destructive invasive animals in the U.S. — now meet 11 others]

The beetle’s journey to Maryland, experts believe, probably began when the species hitched a ride on ash trees from Michigan, the first state the ash borers were spotted in. The bugs were found in a Prince George’s County tree nursery in 2003. Today, the ash borer can be found in every county in Maryland.

“It happened all of a sudden,” Harwood said of the infestation, which emerged last spring. Park officials took notice.

“One of the trail volunteers noticed it and brought it to our attention that there was a tree that looked like it had EAB” — emerald ash borer — “just one. And then we get there and it’s acres’-worth of trees that were all completely dead. The tops were starting to shatter out and fall over.”

Though it can take one to three years for emerald ash borers to destroy a tree, Montgomery County park officials say this once slow-moving locomotive is now a speeding bullet. Ash trees in county parks are dying more than 30 times faster than they had last year.

Patrick Harwood, a horticulturist for Montgomery County parks, inspects trees downed by emerald ash borers in Kensington, Md. (Bill O'Leary/The Washington Post)

But the trees fared well in this week’s snowstorm. What does “well” mean for a park where most ash trees are infested by the emerald ash borer?

They didn’t fall down.

Montgomery County is not the first American community to deal with the ash borer’s destruction. The beetle is found in more than 20 states, as far south as Louisiana and Georgia and as far north as Minnesota and New Hampshire. They’ve also been found in Canada.

[A destructive beetle threatens trees — and people who live near them]

One of the first recorded American emerald ash borer outbreaks occurred in the summer of 2002 near Detroit. Deb McCullough, an entomology professor at Michigan State University, remembered the first time she examined an affected tree.

“When we took the bark off and saw,’’ the S-shaped trails the emerald ash borer larvae leave behind, “we knew it wasn’t a native insect that does that.”

The trails prevent water and nutrients from flowing through the tree, essentially strangling it from the inside.

“There were six of us and we just looked at it and scratched our heads,” McCullough said of that first encounter with the metallic-green beetle. “I remember going home and telling my husband, I said, ‘I think this is going to be a big deal.’ ”

[Read about how a 2014 winter freeze stopped ash borers and stink bugs cold]

At the time, she said, there was very little written about the life cycle of the beetle. A decade later, here’s what experts know: The beetles live for about a month, and during that time, they emerge, mate, lay eggs and die.

One ash tree can have more than 10,000 larvae in it. They bore into the tree and feed on its living parts. After the 1- to 1.25- inch wormlike larvae feed, they overwinter and emerge as adult green beetles in early spring through D-shaped holes in the tree.

[The emerald ash borer’s domino effect on human health]

Putting an end to the life cycle is the key to saving ash trees. There are insecticide treatments, but they can be costly and don’t save the tree. Researchers are studying — and rearing in labs at the University of Maryland — a wasp native to China that is the emerald ash borer’s natural predator. But specialists say it could take some time.

And time is not on the side of the ash trees. Over the next decade, Jerry Langham, senior arborist for Prince George’s County’s park and planning commission, said the bug could change the landscape of Maryland. Unless the ash trees, which are relatively inexpensive and line many of Maryland’s communities, are treated continually, they could all die.

“It’s moved beyond me trying to get control of it,” said Langham. “It’s mainly removal.”

[Civil War battlefield in Virginia is site of new invasion: emerald ash borers]

In Maryland, after the trees are cut down, there are plans to replant. But some parkgoers wonder about the lasting effect of the infestations.

Richard Baker, 75, bought his house because it was right behind the Rock Creek Trail. He shook his head when he was told about the borers’ devastation.

“When you think of the weeding out of the species, whether it’s a species of trees or animals or birds, all of that is very sad,” Baker said. “At the same time, we cherish what we have. And there is a price to be paid for living in an industrial society. And this is part of the price.”