The most common rodent dealt with in the Northwest is 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. 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. A highly migratory existence and rapid rate of reproduction enable the house mouse to thrive. They can enter the home through a hole as small as a dime and are also able to detect heat loss through any cracks or holes as the weather cools. Signs of infestation are, musty 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.