THE SWALLOWTAILS 57 



All our species belong to the genus Parnassius. The 

 caterpillars show their affinity with those of the Swallow- 

 tails by having the curious scent organs or osmateria just 

 back of the head. They feed upon such alpine plants as 

 stonecrop and saxifrage and are well adapted by their 

 structure and habits to the bleak surroundings of the 

 mountain tops. 



As a typical example of the environment in which these 

 butterflies live, we may take the alpine valleys of such 

 mountain regions as Pike's Peak. Prof. M. J. Elrod has 

 described a visit where, at an altitude of 11,500 feet in the 

 month of August, Parnassius smintheus was flying by 

 thousands, and the earlier stages were so abundant that 

 a water ditch had the surface covered as far as one could 

 see with the dead or dying caterpillars. In such situa- 

 tions, where ice forms at night, and snow frequently falls 

 by day, these butterflies develop apparently in greater 

 numbers than almost any of our other species are known to 

 do in warmer regions. 



THE SWALLOWTAILS 



Family Papilionidae 



This is probably the most distinctive family of all our 

 familiar butterffies. Its members are characterized by 

 being on the whole the largest butterflies in our region and 

 by having the hind wings prolonged into curious tail-like 

 projections, suggestive of those of a swallow. In general, 

 the basal color of the wings is blackish though this is com- 

 monly marked in various striking ways with yellow, green, 

 or blue, while the margins of the wings are commonly 



