The Washington State Department of Agriculture (WSDA) is proposing to treat two areas in Snohomish County next spring to eradicate introductions of gypsy moth, a non-native, invasive pest that can decimate the environment. The proposal calls for treating a total of about 1,300 acres at two sites, including one site with the first-ever detection of the Hokkaido gypsy moth in the United States – a type of Asian gypsy moth that predominantly feeds on larch trees in its native environment.

Gypsy moth

WSDA’s proposal involves aerial applications of a soil bacteria called Bacillus thuringiensis var. kurstaki, or Btk, which is a biological insecticide approved for use in organic agriculture. It has an excellent safety record around people, plants, pets, fish, birds and bees and has been used globally for decades as a safe and effective treatment for combating gypsy moth. Treatments occur as gypsy moth caterpillars emerge in the spring and begin to feed on vegetation. Aerial treatments are proposed for the Woodway and Boulevard Bluffs areas.

Gypsy moth caterpillars feed on hundreds of trees and shrubs, often killing these plants in neighborhoods, parks, and forests. The pest also destroys wildlife habitat and some people are allergic to the caterpillars. An infestation can also trigger costly quarantines for timber, Christmas trees, and other forest and nursery products.

This summer and fall, WSDA trapped 14 gypsy moths – 11 European, one Asian (Hokkaido) and two Asian/European hybrid moths. More destructive than its cousin, the Asian gypsy moth and hybrids can feed on a wider variety of trees and the females can fly, so populations can spread more quickly and do more damage to the environment.

Next steps for WSDA include preparing two environmental reviews; consulting with local, state and federal agencies; and public outreach that includes informational open houses. Residents in or near the proposed treatment areas will also receive postcards notifying them of the proposal.

Visit to learn more and find interactive maps of the prosed treatment areas. Gypsy moths were initially detected in Washington in 1974, but no permanent populations have been established here due to WSDA’s successful trapping and treatment program.