480 University of California Publications in Zoology [ V O L - n 



Do PROTECTIVE ADAPTATIONS OF INSECTS PROTECT THEM FROM 

 THE ATTACKS OF BIRDS? 



In the attempt to interpret the law of natural selection 

 emphasis has been laid on the "importance of any structure or 

 character which enables its possessor to escape destruction." As 

 soon as we find that one animal preys on another, we immedi- 

 ately seek for some character to which we can ascribe the sur- 

 vival of the hunted form. This has led to an overemphasis on the 

 theory of protective adaptations. 



Doubtless the interpretation we have put upon certain color 

 characters and other characters called protective have been of 

 value, just as our imperfect systems of classification have been 

 of value. Yet, just as we are constantly changing and modi- 

 fying original classifications, so we may expect to modify our 

 views concerning protective adaptations. 



In order to point out the view usually held, attention is called 

 to the following quotation from Kellogg (1908) : "It has been 

 conclusively shown by observation and experiment, by several 

 naturalists, that many insects are distasteful to birds, lizards 

 and other enemies of the insect class. The blood, lymph or some 

 specially secreted body fluid of these insects contains an acrid or 

 ill-tasting substance, so that birds will not, if they can recog- 

 nize the kind of insect, make any attempt to catch or eat them. ' ' 



Kellogg also goes on to suggest the theory that "success" is 

 dependent on protective adaptations. Certain animals are 

 widespread and found in great numbers and certain others in 

 small numbers. Those existing in great numbers are said to do 

 so because they are protected from their enemies. Enemies are 

 only one factor in the complex that governs the abundance or 

 scarcity of a species, so that such a theory hardly seems justified. 



The examination of so large a number of stomachs of one 

 species of bird has furnished some interesting evidence regarding 

 the extent to which certain insects are protected from their ene- 

 mies. The evidence shows that many of the so-called protective 

 adaptations of insects do not protect them from the attacks of 

 enemies to the extent to which we have been led to believe. 



A recent paper by W. L. McAtee (1912d) of the U. S. Biolog- 

 ical Survey, entitled "The experimental method of testing the 



