INSECTS IN RELATION TO HUMAN WEALTH 571 



for scale lice ; but the following year the shortage in scale lice 

 will reduce the number of ladybirds. The living beings are 

 so related to each other that the elimination or unusual increase 

 in one species is likely to affect the well-being or even the exist- 

 ence of another. Every species has its friends in the living 

 world, as well as its enemies, and when man undertakes to 

 change the numbers of any species, he must proceed cautiously 

 and with a thorough knowledge of all the relations of the spe- 

 cies concerned, and not merely on the basis of a superficial an- 

 swer to the question. Is that species useful or harmful to me? 

 It is not a matter of interfering with nature's plans, as some 

 suppose. It is a matter of disturbing a certain balance that it 

 has taken a long time to establish, with possibilities of unknown 

 consequences. 



When rabbits were introduced into Australia, they multiplied so 

 rapidly that before many years they became a real pest, and the govern- 

 ment offered bounties for their extermination. Here was a region ad- 

 mirably fitted for the hfe of these animals, but until man interfered 

 there had been no such animals there. A similar thing happened with 

 the introduction of the water cress into New Zealand, and with the 

 introduction of the English sparrow into the United States. Probably 

 these organisms throve better in the new surroundings because they did 

 not here meet their old enemies. These facts should help us to realize 

 how closely interdependent the various species of plants and animals are. 



INSECTS IN RELATION TO HUMAN WEALTH 



I. Insects that destroy organic materials, and how to combat them 

 Clothes moth 



Exposure to sunlight and fresh air ; gasoline ; cold storage ; 

 carbon-disulfid fumigation 

 Cockroaches and ants 



Cleanliness about the house; poison with corrosive sublimate; 

 sprinkle borax about 

 Weevils, flour beetle, and flour moth 



Fumigation with carbon disulfid 

 Buffalo moth 

 Gasoline 



