Washington has several species of indigenous squirrels. The two most common causes of human/squirrel conflicts in Central and Western Washington are the Eastern Grey Squirrel and Douglas Squirrels. Eastern grey squirrels, an introduced invasive species, will often out compete native squirrels for natural resources driving the native species out. Douglass squirrels (pineys) are smaller and distinguished by a bronze reddish color. They are aggressively persistent at invading structures.
Their access points are much harder to identify than grey squirrels. Squirrels chew into structures and can be highly destructive. They can chew through almost any building material to access attics or crawl spaces to have their young and cache food. Eastern greys can have 2 litters per year (May-July) with 2-5 pups per litter. Douglass squirrels can have 1-2 litters per year with 3-7 pups per litter. Additionally squirrel access points can pave the way for other pests such as rats, mice and birds.