ADAPTIVE COLORATION 191 



Though butterflies as a group are much subject to the attacks of 

 birds in the tropics, it has been asserted that butterflies in temperate 

 regions are as a whole almost exempt from the attacks of birds, and that 

 consequently the mimicry of the monarch (Fig. 244) by the viceroy is 

 of no advantage. In answer to this assertion Marshall has published a 

 long list of references showing that butterflies are attacked by birds 

 more commonly than has been generally supposed. At the same time 

 there is no proof that the viceroy profits at present by its mimetic pattern, 

 though it may have done so in the past. In any event, the departure of 

 archippus from its congeners toward one of the Danainae a famous 

 group of " models" in the tropics is unintelligible except as an instance 

 of mimicry. 



Granting that mimicry is upon the whole advantageous, it becomes 

 important to learn just how far the advantage extends; and we find that 

 mimicry is not of universal effectiveness. Even the highly protected 

 Heliconiinse and Danainae are food for some predaceous insects. In 

 this country, as Judd has observed, the drone-fly (Eristalis tenax), which 

 mimics the honey bee, is eaten by the kingbird and the phcebe; the 

 kingbird, indeed, eats the honey bee itself, but is said to pick out the 

 drones; chickens also discriminate between drones and workers, eating 

 the former and avoiding the latter. Bumble bees and wasps, imitated 

 by many other insects, are themselves eaten by the kingbird, catbird and 

 several other birds, though it is not known whether the stingless males 

 of these are singled out or not. Such facts as these do not discredit the 

 general theory of mimicry but point out its limits. 



Evolution of Mimicry. Natural selection gives an adequate ex- 

 planation of the evolution of a mimetic pattern. Before accepting this 

 explanation, however, we must inquire: (i) What were the first stages 

 in the development of a mimetic pattern? (2) What evidence is there 

 that every step in this development was vitally useful, as the theory de- 

 mands that it should be? These pertinent questions have been answered 

 by Darwin, Wallace, Miiller, Dixey and several other authorities. 



The incipient mimic must have possessed, to begin with, colors or 

 patterns that were capable of mimetic development; evidently the raw 

 material must have been present. Now Miiller and Dixey in particular 

 have called attention to the fact that many pierids have at least touches 

 of the reds, yellows and other colors that are so conspicuous in the heli- 

 conids. More than this, however, Dixey has demonstrated as appears 

 clearly from his colored figures a complete and gradual transition from 

 a typical non-mimetic pierid, Pieris locusta, to the mimetic pierid 



