172 BRANCH ARTHROPOD A 



The larva when grown is a very light green or greenish yellow, and 

 regularly marked with shiny black and yellow bands. On the second 

 thoracic and the eighth abdominal segment there is a pair of slender, fleshy, 

 black filaments. This caterpillar feeds upon the leaves of the milkweed. 

 It attains its growth in two or three weeks, when it pupates from nine to 

 fifteen days in a smooth, bright green chrysalis (Fig. 142), which is 

 about an inch long and beautifully adorned with a few black and gilt spots 

 and bands. In the South there are two generations, but with us but one. 



The butterfly is protected from its enemies, the birds, by an ill-tasting 

 acrid fluid, of which its conspicuous color gives warning. The power of 

 flight is strong and these butterflies migrate in winter. The monarch 

 is found all over North and South America and in most of the Pacific 

 islands, and in Australia and Western Europe. 



It is closely mimicked by the viceroy (see Fig. 92, p. 119), a smaller 

 butterfly which is not distasteful, but is protected from the birds by its 

 resemblance to the odious monarch. The viceroy may be easily dis- 

 tinguished by the transverse band of black on each of the hind wings. 

 Its larvae feed upon the willow, poplar, and cottonwood. The larva hiber- 

 nates in a silk-lined nest made of a rolled leaf. 



The swallow-tailed butterflies (Papilion'idoe) are a large and interesting 

 family, having a sort of half-fluttering, half-soaring flight. They are 

 easily distinguished by their large size and their black and yellow— or 

 greenish-white — tiger-like markings. Twenty-one species are found in the 

 United States. The wings are very thickly covered with scales. They 

 are narrow and the posterior wings end in a club-shaped prolongation which 

 is supposed to call the attention of the bird to the less vital part. The 

 larvae when disturbed project a pair of bright colored fleshy "horns" from a 

 slit in the dorsal wall of the prothorax. The horns exhale an odor which in 

 some species is exceedingly disargeeable.^ 



The zebra swallow-tail (Iphicll'des a'jax) differs from all other butterflies 

 of the eastern United States by the black and greenish-white bands on its 

 wings and by its exceedingly long " tails." This butterfly is extremely 

 interesting to the scientist, in that it furnishes an example of dimorphism or 

 even of polymorphism. All the broods which hatch out the same summer, 

 and there may be several, are of the same form (ajax), but many individuals 

 pass the winter in the chrysalis stage, some (marcellus) emerging earlj^ in 

 the spring, and some (telamonides) appearing in late spring. The marcellus 

 form has " tails " only about f inch long tipped with white, while the 

 telamonides is a little larger, with tails nearly an inch in length and 

 bordered on each side of their distal half with white; while ajax, the typ- 

 ical form, is still larger and has longer " tails." 



The time of emerging seems to be the only influence controlling this 

 variation, since the offspring of each form, when maturing the same season, 

 produces ajax, when maturing early the following spring, produces marcel- 

 lus, and late the following spring, telamonides. 



The larva of this species is light green, " thickest in the thorax," and with 

 transverse markings of black dots and lines and slender yellow stripes, be- 

 sides a yellow-edged, broad, black, velvety stripe on the thorax. It feeds 

 upon the papaw. 



The tiger swallow-tail {Papil'io tur'nus), another common species, is also 

 dimorphic. In this instance the dimorphism is sexual; at least one of the 

 forms, glaucus, is represented only by the female. 



1 Comstock, r,. 376. 



