THE INSECTS: HEXAPODA 93 



Geographical Distribution of Insects. The map on page 17 

 shows the region of the United States occupied by the Rocky 

 Mountain locust. Within a portion of this area the species 

 is able to maintain itself permanently ; just outside of this 

 area are other regions which are only temporarily occupied, 

 as the great swarms forming periodically seek a new home. 

 That the species is able to maintain itself in one region and 

 not in another is due to its adaptation to a particular region 

 in the matter of food, temperature, climate, absence of over- 

 powering enemies, and other causes. Similar maps might be 

 drawn showing the geographical distribution of all the other 

 insects studied. In each case there would be found some 

 reason why a particular insect did not occupy a larger terri- 

 tory, since, generally, species tend by natural increase to 

 broaden their ranges till hindered by some barrier to their 

 farther advance. To land animals such barrier may be a 

 mountain range, a desert, or a large body of water. To a 

 desert-inhabiting species it might be a forest. To aquatic 

 animals, waterfalls or rapids are often insurmountable. 

 Temperature conditions are very definite in their effects 

 on the distribution of animal life. Food- supply is another 

 important factor. The ocean is a barrier to nearly all land 

 species. 



The animal life of any region is known as its fauna. Though 

 insects are widely distributed over the earth, a study of the 

 different species shows that there are more or less well-marked 

 areas, each of which possesses its characteristic species. 

 Though much overlapping occurs, as might be expected in 

 the case of animals which can fly freely from place to place, 

 yet on the whole it is possible to separate fairly well-marked 

 regions, the climatic and other boundaries of which have 

 prevented any great intercommunication, thus producing 

 peculiar forms of life in each region. These regions may be 

 stated as follows. 



