3 io ECONOMIC ZOOLOGY AND ENTOMOLOGY 



Mice, as a rule, are less serious pests than rats, but the total 

 damage that the common house mouse, M us musculus, does 

 about dwellings and storehouses is very great. This species 

 is a native of India, but has become thoroughly cosmopolitan. 

 Some of the field mice, Microtus sp., frequently do considerable 

 damage in fields of alfalfa or grain and in nurseries and orchards. 

 It is estimated that the damage that they do in the United 

 States amounts to more than $3,000,000 annually. Rarely 

 they occur in great numbers and thus become a veritable 

 plague, devastating large areas. In such outbreaks they are 

 best controlled by placing alfalfa or grain poisoned by arsenic 

 in or at the entrance of their burrows. These plagues rarely 

 last more than a season, as natural enemies and diseases soon 

 reduce the mice to normal numbers. 



The beaver, Castor canadensis, is the largest rodent, weigh- 

 ing sometimes as much as fifty pounds. With their sharp 

 chisel-like teeth beavers cut down small trees in order that they 

 may get at the bark which they use for food. They often 

 build dams of considerable size in order to make a deep pond 

 in which to live and work. The dam is made of trees which 

 have fallen into the stream and sticks of wood of all sizes with 

 the interstices filled with mud. The beavers burrow into the 

 banks or build houses which extend above the surface of the 

 water. The entrance to the burrow is always below the surface. 

 Beavers are much hunted for their fur, which is very valuable. 

 They are so nearly exterminated that they are now found only 

 in a few localities. 



The woodchucks, or ground-hogs, Marmolla spp., are other 

 familiar rodents larger than most members of the order. The 

 chip-munks and ground-squirrels, of which there are several gen- 

 era, are commonly known rodents found all over the country. 

 They are the terrestrial members of the squirrel family, the 

 best known arboreal members of which are the red squirrel, 

 Sciurus hudsonicus, the fox-squirrels, S. ludovicianus and S. 

 niger, and the gray or black squirrel, S. carolinensis. The 

 little flying squirrel, Sciuropterus volans, is abundant in the 

 eastern states. 



The ground-squirrels, commonly known as spermophiles 



