12 AX ECONOMIC STUDY OF FIELD MICE. 
Little understood. So rapidly do they multiply at such times that the 
results arc astonishing. Females become pregnant within a few 
days after giving birth to a litter, and the number of young at a time 
is abnormal. The published accounts of conditions subsequent to 
and during such periods are highly interesting. 
Dr. A. E. Brehm, quoting Blasius and Lenz, states, concerning the 
field mice of Germany (J/, arvalis), that in 182*2 in the district of 
Zabern 1,570,000 were caught in fourteen days. During the same 
time in the district of Nidda 55)0.-127 were caught, and in that of 
Putzbach 271.941. In the autumn of 1856 there were so many voles 
in one district between Erfurt and Gotha that about 12.000 acres of 
land had to be replowed because of the destruction of the first crop. 
On a single large estate near Breslau 200,000 were caught within 
seven weeks and sold to a Breslau fertilizer factory at a pfennig 
(nearly one-fourth cent) per dozen. Some of the vole catchers 
caught 1.400 to 1.500 per day. In the summer of 1861, in the neigh- 
borhood of Alsheim, in Rhenish Hesse, 400.523 were caught. The 
local authorities paid 2,593 gulden (about $1,000) for their capture.' 7 
Louis Figuier, the French naturalist, writing of the same species, 
says that the female gives birth to from eight to twelve little ones 
three or four times in a year, and that multiplication is so rapid at 
times that " whole districts have been reduced to destitution by this 
scourge. In 1816 and 1817- the one department of Vendee experi- 
enced a loss estimated at £120,000 [nearly $600,000], caused entirely 
by these animals." h 
The common meadow mouse of the United States is one of the most 
prolific of our species. Estimating the normal increase at six young, 
with four litters in a season, and assuming that there were no checks 
upon the increase, the results are appalling. A single pair and their 
progeny in five seasons would amount to nearly 1.000.000 indi- 
viduals. This calculation is under the mark, since it is based on the 
assumption that the young do not breed until about a year old. The 
animals, however, mature very rapidly, and the spring young 
undoubtedly breed in the fall of the same year. 
If a thousand pairs of field mice survive the winter in any neigh- 
borhood, the potential conditions for a vole plague are present. If, 
now, instead of normal reproduction, circumstances bring about a 
considerable increase both in the number of young at a time and in 
the number of litters in a season, the probability of a plague is 
greatly increased. Hence the farmer needs the orood offices of every 
creature that preys upon mice, to supplement the climatic limitations 
upon their increase and to aid in saving his crops. 
« Thierleben : Saugetbiere. vol. 2. pp. 3S7-393. 1877. 
& Mammalia Popularly Described by Typical Species, L. Figuier, p. 445, 1870. 
