Nature's Penalty for Interference ' 151 



in great numbers, they would soon become extinct. It is 

 seldom that any one kind of plant or animal, because of its 

 many enemies, has an opportunity to spread and obtain 

 more than its share of food and sunshine. According to 

 Nature's arrangements, each organism does its share in 

 keeping down the numbers of the others. This we call the 

 "balance of Nature." 



Sometimes the balance of Nature is disturbed and one 

 particular kind of animal gets the start of its enemies and 

 increases until it becomes a plague. This may be caused 

 by a favorable season or by the decrease of its enemies on 

 a,ccount of disease among them. We have read of the 

 plagues of grasshoppers which have sometimes visited the 

 Western states and eaten up every green thing. Plagues 

 of rats and field mice have been known to do a great deal 

 of damage. In such cases their natural enemies, the hawks, 

 owls, and coyotes, may be attracted to the region from 

 far around, because of the extra food supply. After a 

 time they may succeed in reducing the numbers of these 

 pests. 



This balance among the animals, which comes from one 

 living upon another, is a strange and wonderful thing. No 

 one kind can long overrun its felloWs. If one does get a 

 start and increases until it becomes a pest or plague, some 

 enemy is sure sooner or later to spring up to destroy it. We 

 use this method in fighting some of the insect pests which 

 are injuring our trees. Men have searched in various parts 

 of the world from which such pests as the g5T)sy moth and 

 the San Jos6 scale have come to find some of their enemies 

 and bring them to this country to feed on these insects. 



When men came upon the earth, they soon began to 



