202 



ELEMENTAKY STUDIES IN INSECT LIFE 



CHAPTEK X 



GEOGRAPHIC DISTRIBUTION AND THE STRUGGLE 



FOR LIFE 



IN the study of physical geography we are accus- 

 tomed to continental maps illustrating land areas 

 bounded and indented by water areas. In political 

 geography, maps show the divisions and subdivisions 

 of countries based upon artificial conditions. Animal 

 geography is another branch of geographical science, in 

 which maps are of value in defining the boundaries of 

 the areas in which animal forms of definite classes 

 exist normally. 



Habitat. - - The geographical range of a species of 

 animal or plant is frequently spoken of as the habitat 

 of the species; that is, the region in which the species 

 lives in a state of nature. From this it might be sup- 

 posed that where the species is originally found there 

 it thrives best, and that there the conditions are ideal 

 for its existence. This is not necessarily so. Of the 

 seventy-three species of insects which occur in the 

 United States in such numbers as to be injurious to 

 man's interests, thirty-seven have undoubtedly been in- 

 troduced from foreign countries. Less than thirty 

 years ago the eggs of the gypsy moth were imported 

 into Massachusetts from Europe. The insect escaped 

 from confinement. No particular attention was paid 

 to this escape. However, in 1890, some twenty years 

 after the introduction the State of Massachusetts 



