8 AN ECONOMIC STUDY OF FIELD MICE. 



when food was exhausted, began to eat each other. They were finally 

 destroyed by an infectious disease, which killed them by thousands. 

 In North America, up to the present time, no such calamitous 

 invasions of field mice have been known, although occasionally one or 

 another species increases locally to such an extent as to amount to 

 a plague. Of even greater consequence, however, is the steady drain 

 on agricultural products caused by these rodents over a large part 

 of the country when present in normal numbers. 



CLASSIFICATION OF FIELD MICE. 



The genus Microtus belongs to a subfamily of Muridce known as 

 the MicrotincB (formerly Arvicotinw) . This subfamily embraces a 

 large number of forms of small and very similar rodents which in 

 some respects resemble true mice, but which are readily distinguished 

 by the robust body, thick head, short ears (whence Microtus), and 

 short tail, the last exceeding two-thirds of the length of the body in 

 but one genus, Fiber (muskrats). 



The Microtince are divided into two groups, which are commonly 

 distinguished under the names lemmings and voles. Externally 

 lemmings have shorter bodies than voles, and, except in one genus 

 (Synaptomys) , the tail is shorter than the hind foot, and the palms 

 and soles are without distinct foot pads (plantar tubercles). The 

 two principal genera have the nails on the thumb strap-shaped 

 (ligulate). 



Voles have bodies less stout, tails usually longer than the hind foot, 

 and* soles and palms always with distinct foot pads. The thumb 

 nails are pointed, not ligulate. There are four genera of voles, all 

 having representatives in the United States, of which the two more 

 familiar are Fiber (the muskrats) and Microtus (the field mice). 

 The other two genera are of little importance to the farmer. The 

 present paper deals only with the genus Microtus. 



Voles of the genus Microtus are distinguished from members of the 

 other three genera by having rootless molars at all stages of their 

 life. Fiber may easily be recognized by its large size, its long, later- 

 ally flattened tail, and by its having the feet modified for swimming. 



There seems to be no entirely appropriate vernacular name for the 

 mice of the genus Microtus. The French call them " campagnols," 

 the Germans " wuhlmause." English-speaking people outside the 

 United States call them " voles." In the United States they are 

 variously designated as " meadow mice " or " field mice," and locally as 

 " bear mice," " bull mice," " buck-tailed mice," " mole mice," etc. 

 "Vole" is open to the objection that it applies equally well to three 

 other genera and may easily be confused with " mole." " Field mice " 



a Report on a Plague of Field Voles in Scotland, Appendix III, p. 76, 1893. 



