An Eastern Washington pest is acting up in the North Cascades

Parts of the North Cascades and Mount Baker are facing an outbreak of the western spruce budworm, aerial surveys reveal.

The outbreak is still early and, compared with past events, modest in size at around 63,500 acres. Nonetheless, the budworm's outbreak in Western Washington is causing some figurative head scratching for Glenn Kohler, an entomologist with the Washington Department of Natural Resources.

It's not unheard of, but it's really unusual," he said. "In the last 20 to 30 years, we haven't seen much western spruce budworm outside of the Cascade crest."

The pest, which is named for its affinity for eating the new growth or buds on fir trees, typically does damage in Eastern Washington. Travelers along Highway 20 may notice the budworm's damage on trees that look slightly orange. By August, the parts of these trees where the budworm has feasted will turn brown and may look dead, Kohler warned.

Hikers traveling in affected areas can identify the hairless worms, which hang by silk, by counting two pairs of white dots on each segment of its roughly inch-long body. The effects of the budworm have been virtually absent for the last six years, though an outbreak in 2011 and 2012 damaged over 500,000 acres of trees.

Each year, DNR and the U.S. Forest Service conduct aerial surveys of Washington's over 20 million acres of forested land to detect for diseases and insect damage that could lead to dying trees.

From 26 flights between July and August last year, officials mapped around 545,000 acres of forest with some level of tree mortality, defoliation or disease, a slight increase from 2023 and a little above the 10-year average of 519,000. The trees were also damaged by nearly three dozen other pests and diseases like the fir engraver and the mountain pine beetle, which damaged around 80,000 and 67,000 acres, respectively.

Officials intend to keep an eye on the western spruce budworm outbreak for now since the insect typically weakens or slows growth after one year, he said. The budworm can kill stands if the outbreak lasts for more than four years, though Kohler said the attacked trees in Western Washington may be able to survive since they receive more precipitation and are "more vigorous."

Research indicates the western spruce budworm outbreaks can follow drought, though it's unclear whether that played a role in the most recent outbreak. The species is native, no stranger to Western Washington and can expand when the conditions are right, Kohler said.

In Washington, 2024 was among the warmest years on record and every month — except May — had an average temperature above what has been observed in the recent century, according to DNR. However, Kohler said the results of drought and warming on trees are typically not seen until the following year.

In general, officials have warned that warmer and hotter summers will lead to more stressed trees, which may make them more susceptible to certain insects. Advocates and public lands officials in Washington have stressed the need to proactively improve the resiliency of forest with thinning and prescribed fires.

DNR Commissioner of Public Lands Dave Upthegrove released a statement saying the report shows the importance of "continuing to increase the pace and scale of not just forest health treatments but monitoring of forest health conditions."

Officials are also keeping an eye on the California fivespined ips, an insect native to Oregon and California that was virtually undetected in Washington before 2010 but has killed "a few dozen pines in recent years around Puget Sound, Kohler said.

In the previous year, arborists have reported dead pines in Discovery Park, the Jefferson Park golf course in Seattle and University Place in Tacoma, he said. The insect's expansion is likely in part due to the heat dome in 2021, which brought record-breaking and fatal temperatures to the Pacific Northwest.

Katie Fields, a forest, fire and communities senior manager with Washington Conservation Action, noted the annual forest health report comes as DNR has received a decreased budget to address forest health and wildfire resilience.

In 2021, the Legislature originally budgeted $500 million over eight years toward forest health treatments like thinning and to help communities prepare for wildfire. However this legislative session due to a shortfall, DNR only received $60 million for the biennium, as opposed to the $125 million the department has received in the past, Fields said.

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