Color in Nature 347 



exclusively on the colors of certain butterflies, whose natural 

 enemies are assumed to be birds, to which they arc supposedly 

 obnoxious through unpleasant taste or odor. Two distinct 

 assumptions are involved in the theory — first that butterflies 

 are the natural prey of birds, and second that certain species 

 are avoided by the latter by reason of some unpleasant 

 characteristic. The first of these hypotheses is founded on 

 very slender evidence. There are, it is true, a few scattered 

 records of birds feeding; on butterflies in nature, but, consider- 

 ing the extent to which birds and butterflies have been studied 

 in the field, these records are few and far between. But, 

 confronted by the paucity of evidence in one direction, the 

 ever facile mind of the Darwinian turns immediately in an- 

 other. Butterflies carry with them, he maintains, evidence 

 of the peril in which they live, in the form of nicks in the 

 hind wings; which, since they frequently have the form of 

 a bird's beak, must be the result of unsuccessful attacks by 

 birds, from which the butterflies have made hairbreadth 

 escapes. But if one studies a series of butterflies taken in 

 late summer or early autumn, he will probably find the wings 

 of nearly all of them torn and broken in such a way that 

 only a little Darwinian imagination is required to conjure 

 up out of all these tattered wings a tale of the tragedies 

 which might have been. The more natural interpretation is 

 however that the butterflies' wings merely show the result 

 of the wear and tear of a summer's flight through field and 

 thicket. 



If butterflies are the natural prey of birds an examination 

 of their stomachs should prove it. Such examinations have 

 been made for many years by the U. S. Biological Survey, 

 in the study of the relation of birds to agriculture, but out of 

 some 80,000 examinations made butterfly remains have been 

 found in but very few. 



The second point involved in the theory has rather more 

 evidence in its support. There are a number of observations 

 on record of birds refusing the strikingly colored and evi- 

 dently distasteful species of butterflies. These observations 

 cover not merely butterflies but other insects also. 



But there is also much evidence to the contrary. Thus 

 Judd, in a number of feeding experiments, has shown that 

 obnoxious forms such as various species of bugs (TIemiptera) 

 whether warningly colored or not are occasionally eaten, as 

 well as stinging insects such as bees. Judd's results must 

 however be accepted with caution, having been obtained with 

 caged birds. It is not certain that captive animals show 

 normal tastes. In some of my own experiments I have found 

 that young birds will eat almost anything which is offered 



