The most common rodent dealt with in the Northwest is the mice entering homes as weather cools looking for a winter home. The house mouse is a grayish brown color on the top and nearly as dark on the bottom (belly), its tail is dusky above and below, nearly hairless and less than half the body length. They have ungrooved incisors.

The gestation period for the house mouse is 18-21 days. They can have several litters per year and each of the litters containing 3-16 young. The house mouse makes its own nest but lives in groups, sharing escape holes and common areas for eating, urinating, and defecating. It takes turns grooming its fellow, especially on the head and back, where it is difficult for the animal to groom it. If the population grows to dense, many females, particularly adolescents, become infertile. A highly migratory existence and rapid rate of reproduction enable the house mouse to thrive.

In such densities, house mice, though generally timid, have been known to run over people's feet and even to bite. These mice eat or their droppings contaminate large quantities of grain and other valuable foodstuffs. They chew or shred anything chewable or shreddable, including furniture and wires, and sometimes start fires. They can scurry up rough vertical walls and even pipes, they gnaw holes in walls, floors, and baseboards. They can enter the home through a hole as small as a dime. They are also able to detect heat escaping through any cracks or holes. House mice can spread disease. Signs of infestation are, musky odour in buildings, small dark droppings, damaged materials, holes in insulation, and shredded nesting material.

Extreme care should be taken when cleaning rodent or bird droppings due to the high probability of disease within.