166 ANIMAL LIFE IN DESERTS 



some other cause. Such cases as this are rare, and 

 I maintain that the theory of protective coloration 

 does not cover more than a few of the phenomena. 

 For instance, among the invertebrata one may find 

 examples of colour which would conceal an animal 

 were its habits not faulty. The hovering flies and 

 bees and wasps to which reference has already 

 been made (page 148) are a case in point ; so are 

 many grasshoppers which climb on a stone and 

 rub their legs together to make a noise, thereby 

 betraying their position by their noise and move- 

 ment. 



I think, then, that we are justified in saying that 

 many creatures whose colours would afford them 

 complete protection if they kept still are rendered 

 easy to see because their movements annul this 

 protection : if the colour has a " protective func- 

 tion," then the habit has an " advertising func- 

 tion " : a theory of advertisement might be launched, 

 and could be almost as well supported as the more 

 popular theory of protection. 



And then how many colours there are which we 

 must frankly say are unsuitable, unless we discard 

 the theory of protective coloration. I have dealt 

 at some length with the black forms earUer in this 

 chapter : let us now consider them from the point 

 of view of theory. Enthusiastic supporters of 

 " protective coloration " have realized that a black 

 and white Wheatear perched on a rock might raise 

 doubts as to the soundness of that theory, and they 

 have urged that these birds are not really conspicu- 

 ous in a bright sun, among dazzling high Hghts and 



