146 BUTTERFLIES 



after the eggs are laid and remain together in crowded 

 colonies that feed upon the upper surface of the aster leaf. 

 At first they eat only the green tissue, leaving the bare 

 veins, although they are not careful to denude the entire 

 surface of the leaf as so many other caterpillars do. As one 

 leaf is exhausted they pass to another near by, continuing 

 thus to feed in companies for a few weeks. Their general 

 color is blackish, although the black is relieved with yellow 

 dots along the back and a band of a similiar color on each 

 side. Unlike the larger social caterpillars of the Mourning 

 Cloak and other butterflies these larvae do not spin any 

 threads as they crawl from place to place, so there is abso- 

 lutely no nest made upon the aster leaf. This may possi- 

 bly be correlated with the fact that these caterpillars are 

 sluggish creatures and when disturbed drop quickly to the 

 soil beneath. 



When the caterpillars are full grown, they fall or crawl 

 to the ground and scatter more or less in search of shelter. 

 Each attaches itself to any protection it may have found 

 and changes to a grayish or brownish chrysalis more or less 

 angular. It remains in this condition for a period that 

 varies greatly with the weather conditions, averaging 

 about two weeks. 



There are two distinct forms of these butterflies which 

 vary so greatly that they were once considered separate 

 species. They are now known, however, to be only sea- 

 sonal variations. In New England two broods of the 

 insect occur, one in spring, the other in summer. The 

 spring form is called technically Phyciodes tharos tharos. 

 In this form the under surface of the hind wings is very 

 distinctly marked with blackish spots. The summer form 

 is called Phyciodes tharos morpheus. It is noticeably 



