742 



AN INTRODUCTION TO ENTOMOLOGY 



tail is replaced as a celery and parsley pest by a related species, 



Papilio zolicaon. 



The tiger swallow- 

 tail, Papilio glaticus. — 

 The larva of this butter- 

 fly (Fig. 949) is even 

 more striking in appear- 

 ance than that of the 

 preceding species. When 

 full grown it is dark 

 green, and bears on each 

 side of the third thoracic 

 segment a large greenish- 

 yellow spot, edged with 

 black, and enclosing 

 small black spots like a 

 figure 10. This cater- 

 pillar has the curious 

 habit of weaving upon 

 a leaf a carpet of silk, 

 upon which it rests when 

 not feeding ; when near- 

 ly full grown, instead of 

 spinning a simple car- 

 pet as before it stretches 

 a web across the hol- 

 low of a leaf and thus 

 makes a spring bed up- 

 on which it sleeps (Fig. 



949)- 



The larva of this 



species feeds on birch, 



poplar, ash, wild cherry, 



fruit-trees, and many 



other trees and shrubs. 

 In the adult state 

 two distinct forms of this insect occur. These 

 differ so greatly in appearance that they were 

 long considered distinct species. They may be 

 distinguished as follows. 



(i) The turnus form, Papilio glaucus tiirnus.^ThQ wings are 

 bright straw-yellow above, and pale, faded straw-yellow beneath, with 

 a very broad black outer margin, in which there is a row of yellow 

 spots. On the fore wings there are four black bars, extending back 

 from the costa; the inner one of these crosses the hind wings also. 

 This form is represented by both sexes, and is found in nearly all 

 parts of the United States and Canada. 



(2) The glaucus form, Papilio glaucus glaucus. — In this form the 

 disk of the wings is entirely black, but the black bands of the turnus 



Fig. 948. — Papilio poly- 

 xenes, larva. 



Fig. 949. — Papilio 

 glaucus, larva upon 

 its bed. 



