7 go POPULAR SCIENCE MONTHLY. 



travel at night, but their march is not continuous, for they make long 

 halts in fertile spots, where they are even more prolific than they were 

 at home, so that they become more and more numerous, although 

 they are attended by bears, wolves, foxes, dogs, and cats, and by 

 hawks and owls, and other beasts and birds of prey, and although 

 even the cattle and reindeer are said to kill and eat them. The 

 march may last for several years, but as they never go back, but con- 

 tinue to move forward, they at last reach the ocean, and, attempting 

 to swim this as they have all the rivers in their course, all are 

 drowned. 



While the migration of the lemmings is undoubtedly due to 

 scarcity, it is difficult to understand its use, for at the present day 

 the only ones to profit by it are those who have the instinct least de- 

 veloped and stay at home in the mountains, although it may have 

 been useful to the species before the low lands were occupied by 

 man, who now destroys the stragglers and prevents them from scat- 

 tering and finding permanent homes. 



"While the determining influence is the scarcity which comes 

 from overcrowding, we have no reason to believe the lemmings 

 consciously and deliberately set out to find a better feeding ground, 

 or that they have traditions of the rich low lands which attract them 

 as the wealth and luxury of China and Mesopotamia and of the 

 Roman Empire attracted the Tartars and Scythians and Goths from 

 the sterile and desolate northern lands into the fertile homes of 

 southern civilization. 



Their journeys are no doubt initiated by an unconscious impulse, 

 which, before it brought them into conflict with man, was useful in 

 some way to the species; and this seems to be true of the migra- 

 tions of certain prolific species of locusts and grasshoppers, which, 

 inhabiting sandy deserts, often overflow the limits of their natural 

 home, and invade more fertile regions where they are not usually 

 found. While there is no reason to suppose these movements are 

 undertaken through deliberate intention to find new feeding grounds, 

 lack of food is no doubt the chief factor in the development of the 

 migratory instinct of rodents as well as locusts, which latter resemble 

 birds in ability to make long journeys on the wing without rest. 

 The African locust has been met at sea in great clouds more than 

 twelve hundred miles from land, and this species sometimes wanders 

 from its home in Africa to England. 



While the movements of rodents and locusts show that the 

 search for food has much to do with migration, they lack the features 

 which make the migrations of birds so remarkable. They occur at 

 irregular intervals, while the movements of birds are almost as regu- 

 lar as the almanac, for, while sea birds seem much exposed to storms, 



