Norway Rat
According to Washington State University, the Norway rat is the most common species in Washington State. They are commonly confused with roof rats, which are the same size as Norway rats at between 13 and 18 inches in total length. Norway rats build nests closer to the ground than roof rats, and the Norway rats' tail is shorter than the length of its head and body. Norway rats are brown with semi-naked tails, giving them a two-toned look.
Roof Rat
The roof rat is the second most common species of rat in Washington State. They are black or brown in color, and tend to be slightly smaller in bulk than Norway rats. Because they use their tails for balance as they climb heights, it is longer than the length of the head and body. Unlike the daytime Norway rat, the roof rat is a nocturnal rodent and rarely seen during the day. Nests are commonly found in attics and high tree branches.
Ord's Kangaroo Rat
The Ord's kangaroo rat is significantly less common in Washington. According to the University of Washington, they are limited to the southern areas of the primarily in Walla Walla, Benton and Franklin counties. The total length of the Ord's kangaroo rat is between 12 and 17 inches. It inhabits sandy grasslands and open shrub steppes dominated by sagebrush, wheatgrass and shadscale. They are nocturnal rodents which hibernate underground during the winter months.
Bushy-tailed Wood Rat
The bushy-tailed wood rat is also known as the common pack rat. They are found in piney woods and rocky areas of northern United States particularly in Montana. Actually a mouse, the wood rat features large round ears, gray fur and a long squirrellike bushy tail. They become pests because of a tendency to steal shiny items and hide them away in their nests. Nests are found on rocky cliffs, canyons, hollow trees, abandon buildings and house attics.