ADAPTIVE COLORATION 



IQ7 



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frequents. Another grasshopper of the same genus, Trimerotropis 

 saxatilis (Fig. 246) occurs only on rock- surf aces, either bare or lichen- 

 crusted. This grasshopper, mottled with several colors but especially 

 yellow, black and greenish, is conspicuous when flying but indistinguish- 

 able when resting on a patch of lichens (Fig. 246 B) . Where the grass- 

 hopper occurs among lichen-covered rocks, as in southern Illinois, it 

 does not alight by haphazard as a rule, but habitually flies from one 

 patch of lichens to another. 



Instances such as this give support to the opinion that " protective 

 resemblances" are not always merely accidental occurrences; since the 

 protective colors are rendered effective by special habits of the insect. 



246. Trimerotropis saxatilis. A, with wings of right side spread. B, with wings 

 closed, and resting on lichens. Natural size. 



'his particular grasshopper, it may be added, is sluggish, and inclined 

 remain where it alights an advantageous habit under the circum- 

 stances. The case is not so simple as that of a caterpillar that is green 

 simply because it feeds on chlorophylls. 



Adventitious Resemblance. If, instead of hastily ascribing all 

 cases apparently of protective resemblance to the action of natural 

 selection, one inquires into the structural basis of the resemblance in 

 each instance, it is found that some cases can be explained, without the 

 aid of natural selection, as being direct effects of food, light or other 

 primary factors. Such cases, then, are in a sense accidental. For ex- 

 ample, many inconspicuous green insects are green merely because 

 chlorophyll from the food-plant tinges the blood and shows through the 

 skin. If it be argued that natural selection has brought about a thin 

 and transparent skin, it may be replied that the skin of a green cater- 



