FAMILY TYPICAL BUTTERFLIES. 149 



IS double-brooded, tlie first butterflies of the season appear- 

 ing about the last of May and flying into July, often until 

 the middle of the month, when the second brood, which is 

 less abundant than the first, makes its appearance. The 

 eggs, which are subspherical and leaf -green, are laid singly 

 on the ujtper surface of leaves and usually hatch in about 

 eight days. The caterpillar feeds on a greater variety of 

 plants than any yet recorded; in all about a dozen families 

 and thirty or more s^^ecies are already known, among which 

 birch, poplar, ash, and Liriodendron appear to be the favor- 

 ites; when young it feeds at the edge of the leaf and 

 retires after feeding to the middle of the upper side of the 

 drooping leaf, where it spins a silken carpet Avhereon to 

 rest head upward ; as soon as it moults it chooses a fresh 

 leaf for its residence and spins a new carpet, going to some 

 neighboring leaf to feed; when it grows larger (having 

 moulted three times) it spins a web across a new leaf so 

 tightly as to draw the opposite sides somewhat together 

 and to make of the leaf a sort of trough, the web touching 

 the leaf only at the sides and forming an elastic bed where 

 the caterpillar rests, concealed on a side view. The chrysa- 

 lis state lasts two or three weeks in the summer. 



This butterfly is remarkable for being dimorj^hic, but 

 with curious restrictions, the dimorphism being limited 

 sexually and geographically; for in the most southern 

 parts of our district and southward there are two forms of 

 female, one resembling the male, as is invariably the case 

 in the north, the other one in which the black has sup- 

 planted the yellow to such an extent that the stripes can 

 only be vaguely seen. 



