186 



Order RODENTIA 



The skull is readily recognizable by a distinct notch in the 

 tip of each upper incisor as viewed from the side, fig. 74/, and 

 by three longitudinal rows of cusps in each of the upper cheek 

 teeth. Dental formula: I 1/1, C 0/0, Pm 0, M 3/3. 



This is the only mouse in Illinois that has gray or butty 

 under parts, a long, naked tail that is almost the same color all 

 around, and a peculiar notch at the tip of each upper incisor. 



Life History. — The house mouse, like the Norway rat, is an 

 accidentally introduced pest. It lives in dwellings, office build- 

 ings, stores, factories, barns, poultry houses, and sheds, and in 

 the runways of native mice and voles. Frequently, mice of this 

 species move out of houses into yards, gardens, and fields in the 

 spring and back into houses in the fall. They usually dominate 

 native mice, and may forcibly drive them out of an area. 



The house mouse produces litters throughout the year, except 

 for the cold winter months. The female has five or six young 

 per litter. The young can run about at 21 days of age and 

 breed at 42 days. 



In eating habits, this mouse is truly omnivorous. 



Signs. — Gnawed paper, black droppings about ]/\ inch long, 

 or small tracks in the dust beside a building may be evidence of 

 the presence of this mouse. In fields, it is difficult to distinguish 

 between signs of the house mouse, fig. 32, and those of some 

 of the native mice. 



Distribution. — The house mouse, like the Norway rat. is 

 abundant throughout southern Canada and along the Pacific 

 Coast to northern Alaska, the United States, and Mexico. The 



Fig. 101. — House mouse. 



