The house mouse’s Washington map tilts east in a way few mammals’ do. Walla Walla and Whitman counties lead with 120 and 88 records, ahead of King County’s 84, with Yakima, Grant, and Spokane close behind, a distribution that tracks grain country as much as city lights.
The ultimate commensal
An Old World native, the house mouse crossed the Atlantic with European shipping and reached the Pacific Northwest with settlement. It lives wherever people store food, in houses, barns, granaries, and warehouses, and spills into the surrounding farmland as feral populations. Washington’s records reflect that double life, from the wheat belt of the Palouse to the Seattle metro, with outliers at Lake Sammamish, Blake Island, and even Gifford Pinchot National Forest.
Indoors when the weather turns
House mice breed nearly year-round where food and shelter hold, but autumn concentrates them. Washington’s counts peak in October and stay high through November, matching the season when the harvest is in, nights turn cold, and mice push into buildings.
Status in Washington
The house mouse is an introduced species in Washington and does not occur here as a native population; NatureServe assigns it SNA, Not Applicable. Globally it is G5, one of the most widespread mammals on Earth.
Full species profile
