Get ready for a “killing wave” sweeping through the Philadelphia region and those on the hit list are all but certain to die if something isn’t done.

The assassin is not who you’d expect and the victims are all around us.

A beetle known as the emerald ash borer with a 99 percent kill rate is attacking Pennsylvania’s millions and millions of ash trees, according to arborists and forestry experts. And as the state’s top forestry manager says, “You have to assume every one of those ash trees is going to die.”

But there is hope, and Pennsylvania’s environmental officials are hard at work to save as many of what could be 1 billion ash trees across the state, according to estimates.

But first, how and when did this bugger of a problem arise?

The emerald ash borer is native to Asia and arrived in the United States as long ago as the late 1980s. It was first discovered feeding on ash trees in the Detroit, Michigan, region in 2002. Experts now believe it was killing ashes for years before that.

How it got to the states is a good question, but it has traveled throughout much of the country in firewood -- the beetle is now found in at least 27 states, and still spreading.

“It’s in virtually every county in Pennsylvania,” said Donald Eggen, the forest health manager for the Pennsylvania Department of Conservation and Natural Resources (DCNR). “It’s been as simple as someone’s ash tree dies, and they say, let’s bring the wood up to the campsite. That’s how it spreads.”

An estimated 306 million ash trees make up four percent of Pennsylvania’s regular forests. (That doesn’t count the millions more in the state’s “urbanized” forests.) About 12 percent, or 37 million ash trees in state forests have already died at the pinchers of the emerald ash borer, which lays its eggs under the bark of the trees. The larva then eat their way along the inner bark and cambium of the tree, which cuts off nutrition and growth.

Within a couple years, an infected ash tree cannot be saved.

“You can’t treat your tree at that point and bring it back to life,” Eggen said.

But, he and local arborists say, there is still hope.

“Eastern Pennsylvania still has a chance,” Eggen said.

Certified arborists like John Verbrugge, of Arader Tree Service in Conshohocken, have been trained to treat ash trees with a pesticide that can protest the trees for two to five years.

Verbrugge, who estimates there are more than 2 million ashes in the Philadelphia region, said it’s worth the cost if homeowners value their mature ash trees. He showed NBC10.com a Lower Merion home’s ash trees and how to treat them. (See the video above.)

But experts like Eggen and Verbrugge agree that treatment must begin ahead of that “killing wave.”

Eggen’s staff at the DCNR already has been working for years with towns to develop municipal-wide plans to manage the beetle insurrection, particularly because dying and dead ash trees also present safety hazards.

“These trees are really brittle when they die,” Eggen said. “You can’t climb one of them to cut from the top down because the branches will break off.”

The state Division of Forest Health is in the midst of studying the ongoing prevention efforts in 10 towns, including West Chester, Philadelphia and Lancaster.

In addition to pesticide treatment, the state spent years in conjunction with the federal government studying the effects a “parasitoid wasp” has on culling the emerald ash borer population, Eggen said.

New tolerant strains of ash trees have also been developed in laboratories in the last decade.

“The beetle is killing 99 percent of the ash trees, so what is happening with the other one percent?” Eggen said. “That’s what we’re looking at.”

It’s not just the loss of beautiful trees in your backyard and nearby parks and the safety issues from millions of trees falling on paths and roads and sidewalks. The ash tree is a part of American culture.

In some areas of the northern Midwest, the black ash tree is sacred to Native Americans. In the large forests of northern Pennsylvania and southern New York, the ash population is cultivated for most of Louisville Slugger’s bats.

“They may have to eventually go to aluminum,” Eggen said of Major League baseball. He wasn’t joking.