A deadly new enemy to Denver’s 330,000 ash trees just moved to town.

The emerald ash borer, an invasive insect that has killed millions of trees across the United States, was discovered in several trees in the Congress Park neighborhood on June 17, city Parks and Recreation officials said Thursday.

City officials confirmed the wood-boring beetle’s presence with Colorado State University entomology experts and Denver’s forestry office.

“We’re grateful that our Office of the City Forester has been preparing for this inevitable discovery, yet this is not a low-stakes battle,” Parks and Recreation Executive Director Jolon Clark said in a statement.

Emerald ash borer beetles were first discovered in Michigan in 2002 and have since killed millions of ash trees nationwide.

They are widely considered the most destructive tree insect ever introduced to North America, according to the state forest service.

In Colorado, emerald ash borers were first found in Boulder in 2013 and later spread throughout the state, including into Broomfield, Fort Collins, Littleton, Carbondale and — last year — Lakewood.

The small-but-destructive green pests invade healthy and stressed ash trees, killing them as soon as two years after the infestation starts. They pose a significant threat to Colorado’s urban forests, 15% of which are ash trees, state officials said.

Denver has been preparing for the arrival of the emerald ash borer since 2016 through public education, replacing small ash trees on city land and rigorous treatment of historic ash trees on city property, officials said.

So far, city foresters have removed more than 1,000 ash trees, treated 6,000 ash trees in parks and parkways, and planted 1,500 trees per year to make up for the loss to Denver’s tree canopy.

Treating ash trees for emerald ash borers is effective 95% of the time when done correctly, according to the city.

Foresters and city workers are “in this for the long haul,” city forester Luke Killoran said.

“We simply can’t stress enough how important it is for Denver residents to take action when it comes to identifying, treating and/or replacing their ash trees as soon as possible,” he said.

Denverites can learn more about the city’s public awareness campaign, “Be a Smart Ash,” and apply for a free replacement tree online at beasmartash.org.