The house mouse has a head-body length of three to three and one-half inches. Its tail is about three to three and three-fourths inches long. The back fur is black or gray. The belly fur is gray or buff while the feet are gray-brown. The prominent ears have few hairs on them. The ringed, scaly, nearly hairless tail is the same color as the back. When looked at from the side, a notch may be seen at the tip of each upper incisor.
The house mouse may be found statewide in Illinois. It lives in fields or buildings. This rodent will eat any human food, livestock feed, seeds, fruits and insect larvae. It is a good climber and swimmer. This mouse is primarily nocturnal. Mating may occur throughout the year. The gestation period is about three weeks. Litter size ranges from two to 10, and a female may produce five or six litters each year. Young are born helpless but develop rapidly. A female attains sexual maturity at the age of about one and one-half months. The house mouse was introduced to the United States from Europe by humans.