10 AN ECONOMIC STUDY OF FIELD MICE. 



Britain (M. agrestis), common from the Orkney Islands to the 

 .English Channel, is also distributed over much of northern Europe. 

 Another closely related species, M. arvalis, has a still wider distribu- 

 tion in central and southern Europe, and, strange to relate, is found 

 in England as a fossil. 



On the other hand, some of the species of Microtus are of limited 

 range, a few of them being confined to the summit of a single moun- 

 tain or isolated on a single small island. The beach vole, for in- 

 stance, occurs only on Muskeget Island, Massachusetts, while the 

 Gull Island vole (M. nesophihis') of Great Gull Island, in Long- 

 Island Sound, was of such limited distribution that grading and 

 excavating for fortifications probably resulted in the total extinction 

 of the species. 



The several species differ greatly in size. Including the tail, some 

 are even shorter than the common house mouse, while others are as 

 large as a medium-sized rat. The largest species is the Florida 

 water rat (Microtus alleni), whose total length is about 320 mm. (12.5 

 inches). The smallest American species is the dwarf vole (M. pau- 

 perrimus), whose total length is 115 mm. (4.5 inches). While the 

 tail of field mice is usually very short in proportion to total length 

 of the animal, the various species differ greatly in this particular. 

 The males of many species give off a strong odor, much like that of 

 the muskrat. 



HABITS OF FIELD MICE. 



While the food habits of the various species of short-tailed field 

 mice are remarkably similar, their breeding and general habits differ 

 greatly. The variety of habitats is most striking. Some species pre- 

 fer high and dry ground, while others live in low, moist places. Oc- 

 casionally the same species inhabits both sorts of localities. Some 

 species live in forests, others in the open prairies. Some burrow 

 under the ground like moles, while others make smooth paths or trails 

 upon its surface. 



Except in cold weather, nearly all species can temporarily adapt 

 themselves to moist surroundings; but a few seem to be almost as 

 aquatic as the nearly-allied muskrat. This is true especially of the 

 larger species, such as the Florida round-tailed " muskrat " (M. alleni) 

 and the European water vole (M. amphibius) , both of which swim 

 and dive with such facility that they are popularly called " water 

 rats." 



NESTS AND TRAILS. 



The nests of field mice are compact bunches or globes, composed 

 chiefly of grass blades and other dry vegetable fibers. They are 

 placed in depressions in the ground, in shallow burrows, or supported 

 on grass stems above the ground. In brush piles the writer has 



