INSECTS 



235 



The monarch and viceroy butterflies; the latter (at the 

 right) is a mimic. 



hundred miles at sea. 

 They may migrate 

 southward upon th€ 

 approach of the cold 

 weather. Some com- 

 mon forms, as the 

 mourning cloak (Va- 

 nessa antiopa), hiber- 

 nate in the North, 

 passing the cold 

 weather under stones or overhanging clods of earth. 



Mimicry. — The monarch butterfly is an example of a race which 

 has received protection from enemies in the struggle for life, 

 because of its nauseous taste and, perhaps, because its caterpillar 

 feeds on plants of no commercial value. 



Another butterfly, less favored by nature, resembles the monarch 

 in outward appearance. This is the viceroy (Basilarchia archip- 

 pus). It seems probable that in the early history^ of the species 

 called viceroy some of this edible form escaped from the 

 birds because they resembled in color and form the species of 

 inedible monarchs. These favored individuals produced new 

 butterflies which resembled the monarch more closely. So for 

 generation after generation the ojies which were most like the 

 inedible species were left, the others becoming the food of birds. 

 Ultimately a species of butterflies was formed that owed its 

 existence to the fact that it resembled another more favored species. 

 This is known as mimicry, and the viceroy is called a mimic. 



Dimorphism and Polymorphism. — 

 It has been found that, when a but- 

 terfly produces two broods during 

 one season, the individuals in these 

 broods may differ considerably from 

 one another. The tiger swaliow-tail 

 is an example. It has also been 

 found that, if the early pupae are 

 kept in an ice box during part 

 of the summer and then allowed 

 to hatch out with the pupae of 

 the second brood, the forms are 

 then ahke in appearance. It would 

 Hornet mimicked by locust-borer, a beetle. thus seem that the same factors 



