WARNING COLOUES 179 



antagonistic principle would be found in the too com- 

 plete success of the method itself. If a very common 

 insect, forming the chief food of some animal, gained 

 protection in this way, the latter might be forced to 

 devour the unpalatable food in order to avoid starva- 

 tion. And the same result might readily be brought 

 about if a scarce and hard-pressed form adopted the 

 same line, and became dominant, after ousting many 

 species which were important as food. If once an 

 insect- eating species were driven to eat any such 

 insect in spite of the unpleasant taste, it would gradu- 

 ally come to devour it with relish, and the insect 

 would be in great danger of extermination, because 

 of its conspicuous appearance. 



If this reasoning be correct, it is clear that the 

 mode of defence is by no means perfect, and that it 

 depends for its success upon the existence of relatively 

 abundant palatable forms ; in other words, its employ- 

 ment must be strictlv limited. 



Absence of Warning Colours in the seasons when 

 Insect life is scarce 



A very interesting fact in support of this argument 

 is the entire disappearance of all insects with Warning 

 Colours during the seasons when insect life is scarce, 

 and when insect-eating animals are hard pressed for 

 food. And yet, if it were safe to rely on such a mode 

 of defence, the Warning Colours would be especially 



