Deer mouse: A deceptively cute rodent capable of carrying the types of hantavirus that cause HPS (hantavirus pulmonary syndrome) in the US. The deer mouse has big eyes and big ears. Its head and body are normally about 2 to 3 inches long, and the tail adds another 2 to 3 inches in length. It occurs in a variety of colors, from gray to reddish brown, depending on its age. The underbelly is always white and the tail has sharply defined white sides. The deer mouse is found almost everywhere in North America. Usually, the deer mouse likes woodlands, but also turns up in desert areas. Scientific name: Peromyscus maniculatus.