WAKNING COLOURS 185 



have been experimentally shown to be distasteful. 

 The colours which produce the greatest contrast, and 

 therefore the greatest effect, upon the eye of an insect- 

 eating Vertebrate, are black and white, and next to 

 this black (or some very dark colour) and yellow, 

 orange, or red ; and it was found that nearly all 

 unpalatable or dangerous insects were coloured with 

 these tints. The advantage gained by the acquisition 

 of such colours is twofold : they afford the combina- 

 tions which are most conspicuous to an enemy, and 

 their number being small, while nauseous forms are 

 numerous, the continual repetition of the same com- 

 bination becomes a necessity, and this also facilitates 

 the education of enemies. 



There are similarly a few eminently conspicuous 

 and simple patterns. These are alternating rings of 

 different colours, and alternating longitudinal stripes, 

 both especially suited to the cylindrical body-form, 

 such as that of caterpillars, &'c. ; spots upon a back- 

 ground with a contrasted colour, especially suited 

 to a wide expanse such as the wings of Lepidoptera. 

 Every insect which has been proved to be distasteful 

 was found to possess one or other of the above patterns 

 or some combination of them. Here also the frequent 

 similarity of the patterns of nauseous insects is 

 primarily due to the fact that there is only a limited 

 number of appropriate patterns, but also because the 

 repetition is in itself advantageous and has therefore 

 been encouraged by natural selection. 



