THE NYMPHS 



middle segment of the abdomen. The tubercles on the second 

 thoracic segment are club-shaped and spiny. 

 Food-plants. — Willow and poplar. 



This species is remarkable for its resemblance 

 to the monarch (Aiiosia plexippus). But aside 

 from the structural characters separating the two 

 subfamilies which these butterflies represent, the 

 viceroy can be easily distinguished from the 

 species it mimics by its smaller size, and by the 

 presence of a transverse black band on the hind 

 wings. 



It is believed that the resemblance of these two 

 species is not merely accidental, but is a result of 

 the action of the law of natural selection. The 

 butterflies of the family to which the monarch 

 belongs, the milkweed butterflies, are exempt 

 from the attacks of birds. It is supposed that 

 this exemption is due to the possession by these 

 butterflies of a disagreeable odor. With such an 

 odor the conspicuous coloring of the butterflies is 

 protective, the birds soon learning that such but- 

 terflies are not fit for food. And it can be seen 

 that these birds will naturally leave undisturbed 

 any other butterflies that resemble the ill-smelling 

 ones, even though they do not possess a similar 

 odor. According to the theory of natural selec- 

 tion these resemblances have been produced as 



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