10 AN ECONOMIC STUDY OF FIELD MICE. 
Britain (M . ugrestis), common from the Orkney Islands to the 
English Channel, is also distributed over much of northern Europe. 
Another closely related species, M . arvaHs, 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 Mierotus 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 (J/. nesophUus) of Great (lull 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 {Mierotus alleni), whose total length is about 3:20 mm. ( 12.5 
inches). The smallest American species is the dwarf vole (J/, path 
pemmus), 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 . alU n> ) 
and the European water vole (J/, 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 
