THE BUTTERFLY AND ITS ALLIES 21 



explained by the theory of Natural Selection or Darwin- 

 ism. Since either of them is of great utility to the 

 organism, their possession, even to a slight degree, how- 

 ever accidentally gained, will give their possessor an ad- 

 vantage over its neighbors in the Struggle for Existence. 

 Consequently it will be more apt to survive and transmit 

 its peculiarity to its offspring. By this means an adapted 

 race will arise and crowd out the unadapted. 



Types of the Butterflies. The group Papilionidse in- 

 cludes the butterflies which fly by day. An account of 

 the most important follows. The Papilios (Swallow-tails) 

 are our largest butterflies. Here belong the yellow Tiger 

 Swallow-tail (turnus), with black stripes, which is found 

 over nearly the whole United States; and the black Swallow- 

 tail (asterias), whose wings are crossed by rows of yellow 

 spots, and whose hind wing bears an orange, black-eyed 

 spot. Its larvae feed on wild or cultivated umbelliferous 

 plants, especially parsnip leaves. 



The Cabbage-butterflies (Pieris) have white or yellow- 

 ish wings, tipped and spotted with black, or sometimes with 

 orange. They hover over damp spots in roads or fly 

 through garden patches. The larvae are very destructive 

 and feed on cabbage and other cruciferous plants. 



To the Nymphs belong the Angle-wings whose fore 

 wings are notched on their outer edge. Here belongs the 

 butterfly which we sometimes see on warm days in winter 

 or early spring the Mourning-cloak. This has pur- 

 plish brown wings with a broad yellow border, and a 

 row of pale blue spots. The Graptas belong here, too; 

 they may be told by the silver spot on the hind wing. 

 In the Admirals the wings are less deeply notched. 

 The red Admiral is purplish black above, with an 



