CIRCULAR No. 423 JANUARY 1937 



UNITED STATES DEPARTMENT OF AGRICULTURE 

 WASHINGTON, D. C. 



THE HOUSE RAT 



By James Silver, regional director, Bureau of Biological Survey 



CONTENTS 



A public menace 1 



Classification 1 



Introduction and spread 2 



Description 3 



Breeding and other habits 3 



Abundance 4 



Economic status 6 



Destruction of food and other property. . . 6 



Annual losses appalling 7 



Relation to health it 



Bubonic plague. 12 



Page 

 Relation to health— Continued. 



Typhus fever 14 



Spirochetal jaundice 15 



Rat-bite fever 15 



Food poisoning 15 



Tularemia 16 



Rabies 16 



Trichinosis 17 



Other rat-borne diseases . 17 



Rat utilization 17 



Repression of rats 17 



A PUBLIC MENACE 



Ail attempt to name the animal most useful to man would give rise 

 to considerable discussion, but there is no doubt as to the one most 

 inimical to the human race. Standing alone, not only as the most 

 destructive animal economically but also as the most serious menace 

 to the public health, is the common house rat. Of all pests, there- 

 fore, the rat is the one above all others that should be kept under 

 strict control. Facts regarding its relationship to human welfare 

 must be understood in order to promote intolerance toward it, for, 

 except as reduced by disease, the number of rats allowed to live will 

 always be in inverse ratio to man's resistance to them. To cope 

 successfully with the rat it is also essential that the fundamental 

 characteristics and habits of the animal be known. It is the purpose 

 of this circular to make such information available. 



CLASSIFICATION 



Two kinds of rats that come into intimate contact with the people 

 of the United States are included in the general term "house rat." 

 These are the browm rat {Rattus norvegicus) and the black rat (R. 

 rattus). The latter, also commonly called roof rat and ship rat, 

 occurs only in comparatively limited areas, chiefly at seaports and in 

 the Gulf States, so that most of the people of the United States 

 know only the former. Various other common names that are ap- 

 plied to the brown rat — depending upon the locality where it is found 

 and often influenced by its size, color, or environment — are 

 barn rat, wharf rat, sewer rat, gray rat, and Norway rat. Its varia- 

 tion in size and color commonly gives the impression that there are a 

 number of entirely distinct species of rats around city and farm 



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