250 HABITS AND INSTINCTS OP ANIMALS. CHAP. VIII. 



into the plains below., in immense troops ; and, by its 

 incredible numbers, becomes a temporary scourge to 

 the country, devouring the grain and herbage, and 

 committing devastations equal to those caused by an 

 army of locusts. These migrations seldom happen 

 oftener than once in ten years ; and, in some districts, 

 still less frequently. They are supposed to originate 

 from an unusual multiplication of the animals, and a 

 consequent defect of food ; and, perhaps, an instinctive 

 prescience of unfavourable seasons : for it has been 

 observed that their chief migrations are made in the 

 autumn of such years as are followed by a very severe 

 winter. On these occasions they collect themselves 

 into an army, and descend from the mountains into 

 the neighbouring plains in a firm phalanx, moving on 

 in a straight line, resolutely surmounting every ob- 

 stacle: their efforts, undismayed by every danger, 

 cannot be contemplated without astonishment. All 

 who have written on the subject agree that they pro- 

 ceed in a direct course ; so that the ground along which 

 they have passed appears, at a distance, as if it had 

 been ploughed, the grass being devoured to the very 

 roots in numerous stripes or parallel paths, of one or 

 two spans broad, and at the distance of some ells from 

 each other. This army of mice move chiefly by night, 

 or early in the morning, devouring the herbage in such 

 a manner that the surface appears as if burnt. No 

 obstacles alter their route, neither fires, nor deep 

 ravines, nor torrents, nor marshes, nor lakes ; they 

 proceed obstinately in a straight line, and hence it 

 happens that many thousands perish in the waters, and 

 are found dead on "the shores. If & rick of hay or 

 corn occurs in their passage, they eat through it j but 

 if rocks intervene, which they cannot pass, they go 

 round, and then resume their former straight direction. 

 If disturbed or pursued while swimming over a lake, 

 and their phalanx separated by oars or poles, they will 

 not recede, but keep swimming directly on, and soon 

 get into order again : they have even sometimes been 



