RODENT PESTS OF THE FARM. 13 



counties that were the center of infection, a wide zone now compara- 

 tively free from squirrels. The Department of Agriculture, through 

 the Bureau of Biological Survey, has exterminated most of the 

 squirrels in the national forests that lie near the plague-infected 

 counties. It is probable that all immediate danger of an outbreak 

 of human plague by infection from ground squirrels has passed. 



Another large and destructive species is the Columbia ground 

 squirrel * (see illustration on title-page). It occurs within the United 

 States in parts of Montana, Idaho, eastern Washington, and eastern 

 Oregon. While it inhabits chiefly the river valleys, it has been taken 

 in Montana on mountains near timberline. Where grain is gpown 



FK;. 0. Mound of California ground squirrel in oats field. 



in the narrow valleys and in the important wheat districts of eastern 

 Washington this species is extremely injurious. Early attempts to 

 destroy it by poison proved unsuccessful, because the animal is able 

 to resist much larger doses of strychnin than are needed to kill 

 other ground squirrels. 



A destructive and widely distributed species is the Richardson 

 ground squirrel. 2 In its larger form it is found in much of Montana, 

 the Dakotas, and northward into Canada. A somewhat smaller 

 race (elegans) is found in southeastern Oregon, northern Nevada, 

 southern and eastern Idaho, southern Wyoming, and northern Colo- 

 rado. This spermophile is very destructive to crops, especially to 



- CitcUus richardsoni richardsoni and CitcUu.* richardsoni 



