ANIMAL, COUNTERFEITS. 245 



Among mammals the skunk is a strikingly colored as well as a strongly 

 scented animal. But why tell of warning coloration in a study of coun- 

 terfeit? You say surely the bees are an honest self respecting folk. So 

 they are, but we must understand what freedom from annoyance or sk- 

 termination they enjoy and then we are fully prepared to comprehend 

 the beautiful scheme by which nature protects her own from her own. 

 Let us look for a moment at the Anosia plexippus (Plate L.) a butterfly 

 of tropical origin, which migrates northward in the spring time, lays 

 eggs for a spring brood which complete the cycle and migrate further 

 northward. The fall brood migrate southward in September. There is 

 no easier butterfly to raise from the egg which may be found on the com- 

 mon milkweeds. Why does this butterfly enjoy such a freedom of flight? 

 It is found upon trial that birds forcibly fed upon the adult Anosia 

 become very sick. It would seem that the birds have either tried the ex- 

 periment or are warned in some way from doing so. They therefore never 

 touch brown butterflies of this size with a black bordered wing bearing 

 a row of white spots. 



Let us now look at representative members of a widely separated 

 genus, the Basilarchias (Plate L.) We find them to be generally purple 

 in color with white or brownish markings. The common species of this 

 genus in Montana has a broad white band on the forewings. In habit 

 they are shy and flit from one bush to another. 



One species of this genus differs radically from the others in coloring 

 and habit. It is the species disippus. It is almost a perfect copy of the 

 Anosia just described. It also has the habits of that insect. The early 

 entomologists, who made the classification a matter largely of external 

 appearance, very naturally classified the two together. In tact they are 

 so nearly alike that they deceive everyone but the trained entomologist 

 who looks beneath outward appearances. They differ in that the Basil- 

 archias are edible when birds can be induced to try to eat them. This is 

 doubtless a very rare occurence in nature owing to the perfect re- 

 semblance to the undesirable species. 



Wallace states the conditions necessary in order to effect mimicry are 

 follows : 



1. The two species, the imitating and imitated, must occur in the 

 same locality. 



2. The imitating species must be the more defenseless. 



3. The imitating species must be the less numerous. 



4. The imitating species must differ from its allies. 



5. The imitation is external only, affecting only external appearances. 

 As to the origin of such a species some think that it must have come 



from Basilarchia astyanax, the common species of the middle states, 

 which is sprinkled with brown spots. It may be that certain individuals 

 differed from the current stock in being nearly or entirely brown. A 

 sudden variation to a widely different type is called a sport and occurs 

 in all species. If the sport came near enough the Anosia in color to be 

 mistaken by its enemies for an edible species, it would be likely to live 

 to reproduce. From the eggs of such an insect perhaps only a few 

 would resemble the parent but these few would stand the better chance of 



