LEPIDOPTERA 



263 



ern parts of Canada. In California the black swallow-tail is replaced as a 

 celery and parsley pest by a related species, Papilio zolicaon. 



The tiger swallow-tail, Papilio glaucus. — The larva of this butter- 

 fly (Fig. 458) is even more striking in appearance 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 a small black figure 10. This caterpillar 

 has the curious habit of weaving upon a leaf a carpet 

 of silk, upon which it rests when not feeding; when 

 nearly full-grown, instead of spinning a simple carpet 

 as before, it stretches a web across the hollow of a leaf 

 and thus makes a spring bed upon which it sleeps 

 (Fig. 458). 



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. 



(1) The turnus form, Papilio glaucus turnus. — 

 The 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 yel- 

 low 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 

 form are faintly indicated, espe- 

 cially on the lower surface, by a 

 darker shade. The marginal row of 

 yellow spots is present, and also the 

 orange spots and blue scales of the 

 hind wings. This form is repre- 

 sented only by the female sex, and 

 occurs only in the more southern 

 part of the range of the species, i.e., 

 from Long Island to Montana and 

 southward. It was the first of the 

 two forms to be described, hence 

 the species bears the name glau- 

 cus. 



The zebra swallow-tail, Iphiclides marcellus. — This butterfly (Fig. 

 459) differs from all other swallow-tails found in the eastern half of the 

 United States in having the wings crossed by several bands of greenish- 

 white. This is one of the most interesting of our butterflies, as it occurs 

 under three distinct forms, two of which were considered for a long time 



Fig. 458. — Papilio glau- 

 cus, larva upon its bed. 



Fig. 459. — Iphiclides marcellus. 



