MAMMALIA 



247 



most parts of North America, and at times have been known, for some 

 reason, to increase to such an extent as to be a most serious pest. 

 They produce several litters a year, with from 5 to 10 in a litter. 



FIG. 157. Apple tree 5 inches in diameter girdled by prairie meadow mice, Microtus 

 austerus. (From Lantz, Meadow Mice in Relation to Agriculture.) 



The meadow mice are injurious to crops of all kinds, grain, vege- 

 tables and fruit. When in especially large numbers their damage is 

 proportionately greater; for example: in 1906-8 a pest of meadow mice 

 destroyed the alfalfa crop over an area of some 18,000 acres in Nevada, 



