Washington State is actively fighting several invasive beetle species that threaten its forests, urban trees, and agricultural crops. The most pressing current infestations involve the Japanese beetle in south-central Washington and the newly detected emerald ash borer near Vancouver. Other species, including the Asian longhorned beetle, haven’t been found in the state yet but pose enough risk that Washington enacted a statewide firewood quarantine in 2026 specifically to keep them out.
Japanese Beetle
The Japanese beetle is Washington’s most active invasive beetle problem right now. Native to northern Japan, the metallic green-and-copper adults are only about 3/8 inch long but can feed on hundreds of different plant species, from native vegetation to common garden and landscaping plants. Adults eat leaves while larvae attack roots, especially grass roots. Plants already under stress before an infestation may not survive.
Washington’s infestation started small. In 2020, the state Department of Agriculture found two beetles near Grandview and one near Sunnyside in the Yakima Valley. It grew rapidly. Beetles now turn up in Pasco and Wapato as well, and tens of thousands are trapped each year across south-central Washington. A multi-year eradication effort is underway, and an emergency quarantine covers parts of Yakima and Benton counties, with restrictions also relevant to workers in Franklin County. The quarantine was most recently expanded in April 2026.
In 2024, 32 Japanese beetles were captured in King County near Seattle-Tacoma International Airport, a worrying sign that the pest could gain a foothold in the state’s most populated region. Trapping in that area is set to begin in 2025. If you live or garden in these areas, keep an eye out for adults with white fuzzy tufts along the edges of their abdomens, just below each wing. The larvae are white grubs in soil that look nearly identical to many native species, making them hard to identify without expert help.
Emerald Ash Borer
The emerald ash borer has been called the most destructive forest insect ever to reach North America, and Washington confirmed its first detection near Vancouver. Every true ash species is vulnerable, including Oregon ash, the only ash native to the Pacific Northwest. A state Department of Natural Resources analysis found that without active management, a city should expect to lose 90 to 100 percent of its ash trees within 10 to 12 years of an initial infestation.
There is no sugarcoating the outlook here: no one has ever successfully eradicated the emerald ash borer once it establishes. The only proven strategies are limiting firewood transport, removing infested trees, and replacing them with non-ash species. Dozens of cities across the eastern United States and Canada have already lost their ash canopy entirely. Washington’s detection puts the state’s urban and riparian ash trees, many of which line riverbanks and provide critical shade for salmon streams, in serious jeopardy.
Asian Longhorned Beetle
The Asian longhorned beetle has not been detected in Washington, but it ranks among the state’s highest-priority threats. It targets hardwoods like maple, birch, elm, and willow, boring deep into trunks and branches in a way that eventually kills the tree. Washington’s Invasive Species Council actively monitors for it alongside the closely related citrus longhorned beetle.
If you think you’ve spotted one, look carefully. Washington has native lookalikes, especially the banded alder borer and several species in the Monochamus genus. Monochamus beetles have smaller white spots, small white triangles on their upper backs, and noticeably rougher, bumpier, less glossy shells compared to the sleek Asian longhorned beetle. Getting the ID right matters because a confirmed sighting would trigger an aggressive response.
Washington’s Firewood Quarantine
One of the most common ways invasive beetles spread across state lines is by hitchhiking in firewood. Larvae and eggs buried inside logs are invisible to the naked eye and can survive long road trips. To address this, Washington adopted a statewide exterior firewood quarantine in February 2026. The rule is straightforward: you cannot bring untreated firewood from outside Washington into the state for sale or personal use.
Any firewood imported into Washington must be heat-treated to a core temperature of at least 160°F for a minimum of 60 minutes, or undergo an equivalent approved treatment. It also needs labeling showing its source and an “Approved Pest Free” statement. Violations carry civil penalties of up to $5,000 per offense, and the Department of Agriculture can impound noncompliant firewood on the spot.
The rule doesn’t apply to firewood harvested and kept within Washington, and it excludes processed wood products like pellets and compressed bricks, as well as logs headed to sawmills, pulp mills, or biomass facilities. The quarantine targets the specific pests most likely to arrive in firewood: emerald ash borer, Asian longhorned beetle, spotted lanternfly, spongy moth, and pinewood nematode, among others.
How to Report a Suspected Invasive Beetle
Public reports are one of the most important early detection tools the state has. If you spot a beetle you can’t identify, or notice unusual tree damage like perfectly round exit holes, peeling bark, or rapid canopy dieback, you can report it through the Washington Invasive Species Council’s website or their mobile app, available on both Apple and Google Play. Your reports help officials identify new threats and track how existing populations are spreading. When possible, take a clear photo of the insect next to a coin for scale, and note the exact location.