IV 



ON THE EVIDENCE THAT BUTTERFLIES ARE 

 PREYED UPON BY BIRDS 



As already noticed, the supposed lack of evidence that birds do in fact exercise a great 

 selective influence on butterflies has always been a strong point in the arguments of those 

 who find a difficulty in accepting the view that mimetic resemblances are produced by natural 

 selection, and it must be admitted that for some time after these problems began to occupy 

 the attention of naturalists the direct evidence in support of the assumption was by no 

 means plentiful. It was argued that if birds are so powerful a selective force the destruction 

 of butterflies by them should be a matter of everyday occurrence, easily observed and 

 accepted without question. A little consideration, however, will show that the subject is 

 by no means so simply and easily dismissed. Are we, as a matter of fact, so very familiar 

 with the details of the everyday life of the wild creatures which surround us ? In temperate 

 regions the diversity of forms of animal life is not developed to anything like the extent 

 which is attained in the tropics. Our sharply-defined seasons materially reduce the oppor- 

 tunity for the rapid reproduction which takes place in regions nearer the equator ; and thus 

 we find that the methods of deception employed by various forms to ensure the survival of 

 their species are much less numerous and diverse than is the case in tropical lands. There 

 we find life manifested in swarming hosts of creatures amongst which the competition for 

 existence is such that only those which have evolved a very perfect adaptation to their 

 surroundings remain as evidence of the struggle. In our own country we have ample oppor- 

 tunity for studying the habits of our native animals, and yet if the question arises as to 

 whether certain birds are, from an economic point of view, destructive or beneficial, large 

 numbers must be shot and their crops examined before anything can be definitely stated 

 as to their habitual food. If we examine the statements of the opponents of the selective 

 theory, it is found that the evidence is largely of a negative character. That birds are not 

 commonly seen to eat butterflies may be a fact, but this is not good evidence that they seldom 

 or never do so, and thus we come to one of the strongest arguments against the kind of nega- 

 tive assumption so frequently proffered, an argument used by Marshall in his paper on 

 'Birds as a Factor in the Production of Mimetic Resemblances in Butterflies ',Hvhich is that, 

 from those who maintain that birds do not eat butterflies, we are justified in demanding 

 a list of the insects which birds have been seen to eat. Before I was aware that Mr. Marshall 

 was making a special study of this subject, I had begun, for the purpose of the present memoir, 

 to collect instances of birds preying on butterflies. My own work in that direction had not, 

 however, proceeded very far when the above-mentioned paper appeared. Needless to say, 

 the work has been carried out with a completeness which I could not have hoped to attain, 

 and as the author, with characteristic generosity, at once placed the paper at my disposal 

 for the present purpose, it must be understood that I am indebted to him for the 

 information here furnished. In the face of the many assurances given from time to time by 



1 Trans. Ent. Soc-. 1909, p. 329 et seq. 



