60 ANIMAL COMPETITORS 



ened to develop into a plague as great as any 

 recorded, and the facts concerning it have been 

 studied and preserved in a pamphlet by Stan- 

 ley E. Piper of the Biological Survey. The 

 species was the black or Carson mouse (Micro- 

 tus montanus), which is widely prevalent west 

 of the Rocky Mountains. 



"The greatest loss occurred in the rich fields of 

 alfalfa bordering Humboldt Kiver for the last ten 

 or twelve miles of its course. Noticeable here through 

 gradually increasing damage during 1906, the field- 

 mice appeared early in the summer of 1907 in alarm- 

 ing numbers. By November they had overrun a 

 large part of the cultivated area, and on many large 

 ranches were estimated to number from 8,000 to 

 12,000 to the acre. Fields were literally honey- 

 combed by their holes, which numbered about 24,000 

 to the acre. During the summer they ruined one- 

 third of the alfalfa, destroyed three-fourths of the 

 potatoes, and severely injured root-crops, as beets and 

 carrots. Upon the disappearance of green food in 

 the fall they attacked the roots of alfalfa, so as to 

 render many alfalfa fields a total loss. They girdled 

 and killed most of the young shade-trees planted 

 along ditches and about the borders of fields, while 

 small orchards suffered severely." 



Decline of the visitation. By January, 1908, 

 the ravages had extended over considerably 



