GEOGRAPHIC DISTRIBUTION 



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the rocky cliff. The Parnassian butterflies, alpine 

 species, seem to require cool climate ; consequently they 

 are to be found in northern countries and in the high 

 altitudes of mountainous regions. The clouded skip- 

 per butterfly seems to thrive in a warm, moist climate. 

 Its habitat, then, in the United States is restricted to a 

 strip of land along the Atlantic seaboard and the Gulf 

 of Mexico. 



While climatic conditions may not be unfavorable, 

 there is still another barrier which in the case of many 

 insects effectually prevents their spread. This is food 

 plants. There are many insects, notably butterflies, 

 which at some stage in their development are dependent 

 upon a certain plant or family of plants for sustenance. 

 The larvae or caterpillars of many butterflies will thrive 

 only upon certain plants. If these plants are wanting in 

 a new territory, it is evident that there will be no in- 

 crease in the respective species. The milkweed but- 

 terfly, already referred to under other phases, is a case 

 in point. The caterpillar of the milkweed butterfly 

 will grow and develop only when feeding upon the 

 leaves of some member of the milkweed family. This 

 insect belongs properly to the tropics, but has now a 

 widespread distribution. It was unknown in Hawaii 

 until a member of the milkweed family established 

 itself in Hawaii. Similar observations have been made 

 concerning its existence on a number of other oceanic 

 islands subsequent to the natural growth thereon of the 

 milkweed. 



Fauna. - The term " fauna " is used to designate the 

 animal life of any district. The fauna of Iowa, for 

 instance, refers to all the animal life in a state of nature 



