NATURAL HISTORY OF THE RAT. 



By David E. Lantz. 

 Assistant, U. S. Biological Survey, Department of Agriculture. 



INTRODUCTION. 



The extermination of rats has become one of the serious problems 

 of modern times. That such noxious animals should have flour- 

 ished so long is not creditable to our civilization. "V\Tiile no kind of 

 rat can be regarded as harmless, the various species dififer greatly 

 in harmfulness. In comparison with the cosmopolitan species that 

 have, reached our shores from the Old World, our native rats do 

 little damage.. It is important, therefore, to be able f,o recognize 

 the introduced forms, to understand their habits, and to concentrate 

 efforts for their extirpation. 



CLASSIFICATION OF RATS. 



Rats and mice belong to the Bodentia, an order which comprises 

 more than a third of all living^'species of mammals. Also, it exceeds 

 any other mammalian order in the number of its individuals. 



Rodents are mainly herbivorous mammals, mostly of small size, 

 having a furry, sometimes a spiny, integument, clawed digits, and 

 usually plantigrade feet. The most important distinguishing char- 

 acter of the order is its dentition. This is marked by the absence 

 of canine teeth and the presence of stroilgly developed incisors 

 growing from permanent pulps. The incisors are never more than 

 two in the lower jaw and usually but two in the upper. They are 

 elongated, curved, chisel-like in shape, and continue to grow through- 

 out the life of the animal. Only the front of these teeth is covered 

 with enamel, a provision which keeps them sharp by the more rapid 

 wearing away of the softer dentine in the body of the tooth, as the 

 upper and lower pairs meet in gnawing. Between the incisors and 

 the cheek, or molar, teeth of rodents there is a wide, vacant space, 

 marking the entire absence of canines. 



The most extensive family of rodents is the Muridse, a name which 

 applies to rats and mice in the widest sense of those terms. It is 

 difficult to characterize the family, since it members differ widely. 

 However, most of them are rat-like in form and light and active in 



(16), 



