LEPIDOPTERA . 
409 
that resemble the ill-smelling ones, even though they do not 
possess a similar odor. According to the theory of natural 
selection these resemblances have been produced as follows. 
In the case of a variable species that is unprotected by any 
disagreeable quality, any variation towards a protected spe¬ 
cies will tend to preserve the life of the individual possessing 
it. And in turn such offspring of these individuals as still 
more nearly resemble the protected species will be most 
likely to be preserved. The continued action of this natural 
selection will result in producing a species that closely re¬ 
sembles the protected one, even though it may be very 
different structurally from the one that it mimics. 
Many instances of unconscious mimicry of this kind are 
known. They are especially abundant in the tropics where 
the foul-smelling Heliconince are most abundant. The bad 
odor of these butterflies when living is so marked that it 
can be detected by the human nose; and it is found that 
many species of them are mimicked by other butterflies, and 
especially those of the Pieridae. The mimicry is not con¬ 
fined to similarity in coloring, but extends to the shape of 
the wings and manner of flight. 
The larva of the Viceroy feeds upon willow, poplar, balm 
of gilead, aspen, and cottonwood. The species two- or three- 
brooded, and hibernates as a partially grown larva in a 
nest made of a rolled leaf. This nest is lined with silk, 
and the leaf is fastened to the twig with silk so that it can¬ 
not fall during the winter. Mr. Scudder states that so far 
as is known to him all of the species of the Sovereigns hi¬ 
bernate as larvae in nests of this kind. It is worthy of note 
that only the autumn brood of caterpillars make these nests. 
So that the nest-building instinct appears only in alternate 
generations, or even less frequently when the species is 
more than two-brooded. B. archippus is found over nearly 
the whole of the United States as far west as the Sierra 
Nevada Mountains, and has been found sparingly even to 
the Pacific coast near our northern boundaries. 
