12 AX ECONOMIC STUDY OF FIELD MICE. 



little understood. So rapidly do thev multiply at such times that the 

 results are 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 1822 in the district of 

 Zabern 1,570.000 were caught in fourteen days. During the same 

 time in the district of Xidda 590,127 were caught, and in that of 

 Putzbach 271.911. 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 reploAved 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 1,100 to 1,500 per day. In the summer of 1861, in the neigh- 

 borhood of Alsheim. in Rhenish Hesse, 109,523 were caught. The 

 local authorities paid 2.593 gulden (about $1,000) for their capture." 



Louis Figuier, the I'rench 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." * 



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 good offices of every 

 creature that prejs upon mice, to supplement the climatic limitations 

 upon their increase and to aid in saving his crops. 



a Thierleben : Sjiugethiere. vol. 2. pp. 387-393. 1877. 



i Mammalia Popularly Described by Typical Species, L. Figuier, p. 445, 1870. 



