DISTRIBUTION OF EATS IN AMERICA. 11 



The present bulletin is intended to acquaint the public with the 

 habits of the brown rat, a the nature and extent of the losses inflicted 

 by it, and the best available methods of fighting it. It is believed 

 that such knowledge will result in more persistent attempts, through 

 cooperation and individual effort, to exterminate the pest, or at least 

 permanently to reduce its numbers. 



DISTRIBUTION OF THE GENUS MUS IN AMERICA. 



True rats and mice belong to the Old World genus Mus, of which 

 nearly 300 species have been described. Of these about seven- 

 eighths are properly to be classed as rats and the remaining one- 

 eighth as mice. Among all the species of Mus four have developed 

 the ability to adapt themselves to such a variety of conditions as to 

 climate and food that, carried on ships, they have established them- 

 selves in many parts of the world. These four are the only species 

 of Mus that have become acclimatized in America. 



The common house mouse (Mus musculus) found its way to 

 America soon after the first settlement by Europeans. It is now 

 distributed in all settled parts of North and South America, but in 

 the extreme north it does not always survive the winters, and is 

 therefore scarce. 



The black rat (Mus rattus) (PL I, fig. 2) was carried to South and 

 Middle America about three and a half centuries ago. The time of 

 its arrival in the English colonies of North America is uncertain, but 

 it was well established in the settled portions by the beginning of the 

 eighteenth century. After the arrival of the brown rat, it began to 

 decrease in numbers and gradually Jo disappear until it has become 

 rare in most parts of the United States and Canada. It is now found 

 in scattered colonies mostly east of the Mississippi Valley and on 

 certain islands along the coast on both sides of the continent. It is 

 occasionally observed in most of our seaports. The Biological 

 Survey has specimens from Massachusetts, New Hampshire, Georgia, 

 Florida, Alabama, California, and Washington, as well as from 

 Mexico, Honduras, Nicaragua, and Hawaii. Also there are authentic 

 records of its recent occurrence in Newfoundland, Quebec, Nova 

 Scotia, New York, North Carolina, Tennessee, West Virginia, and 

 Mississippi. In parts of South and Middle America the black rat 

 has been more persistent and is still abundant. 



The roof, or Alexandrian, rat ( Mus alexandrinus) is similar to the 

 black rat in form and habits, though not in color. Little is known 



a While this paper deals primarily with the brown rat, some of the illustrative facts 

 quoted throughout the following pages refer to the black rat (Mus rattus) and to the 

 roof rat (Mils alexandrinus). The habits of the three species differ so little that the 

 methods given for combating them apply to all. In some of the discussions of losses 

 caused by rats it has not been practicable to exclude those due to the common house 

 mouse ( Mus musculus) . 



