412 THE STUDY OF INSECTS. 



The larvae of both of these species feed upon grass ; 

 the butterflies fly during the latter half of the summer, 

 and the larvae begin hibernating as soon as hatched. 



The Hybrid Graylings, Cercyonis alope-nephele. — The 

 Dull-eyed Grayling is a northern species, occurring in 

 Canada and the northern part of the United States. The 

 Blue-eyed Grayling is found throughout the greater part of 

 the United States east of the Rocky Mountains, except in 

 the extreme North and South. The ranges of the two 

 overlap in the southern portions of New England, New 

 York, Michigan, Wisconsin, Iowa, and Nebraska; and in the 

 northern portions of Illinois, Indiana, and Ohio. In this 

 belt both species occur, and also intergrades between them ; 

 these intergrades may be called Hybrid Graylings. 



The White Mountain Butterfly, CEneis semidea (CE-ne'is 

 se-mid'e-a). — Comparatively few students who study this 

 book will collect this butterfly ; but we refer to it on ac- 

 count of its remarkable distribution. It is found only on 

 the higher parts (above 5000 feet) of the White Mountains 

 in New Hampshire, and on the highest peaks of the Rocky 

 Mountains of Colorado, above 12,000 feet. 



These two widely separated colonies of this butterfly are 

 believed to be the remnants of an Arctic fauna which was 

 forced southward during the Ice Age. At the close of this 

 period, as the Arctic animals followed the retreating ice 

 northward, the tops of these mountains became colonized 

 by the cold-loving forms. Here they found a congenial 

 resting place, while the main body of their congeners, which 

 occupied the intervening region, was driven northward by 

 the increasing heat of the lower land. Here they remain, 

 clinging to these islands of cold projecting above the fatal 

 sea of warmth that fills the valleys below. 



