262 



THE STUDY OF INSECTS 



Family Papilionid^e 



The Swallow-tails and the Parnassians 



This family includes the swallow-tail butterflies, which are common 

 throughout our country, and the parnassians, which are found only on 

 high mountains or far north. These insects are distinguished from all 

 other butterflies found in our fauna by the fact that vein M 2 of the fore 

 wings appears to be a branch of cubitus, making this vein appear to be 

 four-branched, and by the fact that the anal area of the hind wings is 

 more reduced than the anal area of the fore wings, the former containing 

 only a single anal vein, the latter two in the parnassians and three in 



the swallow-tails. 



The caterpillars are never 

 clothed with spines but are either 

 naked or clothed with a few fine 

 hairs. In at least one species in 

 our fauna, the body bears fleshy 

 filaments. 



A striking peculiarity of the 

 larvae of this family is the pres- 

 ence of a bright-colored, forked, 

 horn-like process which can be 

 projected from a slit in the dorsal 

 wall of the prothorax. This is 

 the osmeterium which is an organ 

 of defense; for it exhales when pushed out an 

 cdor which in some species is exceedingly dis- 

 agreeable. 



The black swallow-tail, PapUio polyxenes. — 

 The larva of this swallow-tail (Fig. 457) is well- 

 known to most country children. It is the green 

 worm, ringed with black and spotted with yellow, 

 that eats the leaves of caraway in the back yards 

 of country houses. It feeds also on parsnips 

 and other umbelliferous plants. The young larva 

 is black, banded about the middle and caudal 

 end with white. There are two generations 

 annually in the North and at least three in the 

 South. 



In the adult the wings are black, crossed 

 with two rows of yellow spots, and with marginal 

 lunules of the same color. The two rows of 

 spots are much more distinct in the male than in 

 Papiih polyxenes, the female, the inner row on the hind wing forming a 

 continuous band crossed with black lines on the 

 veins. Between the two rows of spots on the hind wings there are many 

 blue scales; these are more abundant in the female. Near the anal angle 

 of the hind wing there is an orange spot with a black center. On the 

 lower surface of the wings the yellow markings become mostly orange 

 and are heavier. 



This species is found throughout the United States and in the south-- 



