Pacicaed.] 



INSECTS AS MIMICS. 



277 



to tlie ground among the leaves of the oak are covered with 

 dead leaves, and the color of the cocoon when bare harmo- 

 nizes with that of the soil or leaves. 



Aquatic insects are often nearly colorless, like the water 

 they inhabit. Many water larvsB are pale green, like the 

 plants in which they hide. What excellent mimics the cad- 

 dis worms and Ranatra and Belostoma are, we have previ- 

 ously adverted to in the chapter on Insects of the Pond and 

 Stream. To the cases there given might be added certain 

 sluggish larvaB like Psephenus (Fig. 215) and others, which 



Fig. 2U. 



Fig. 215. 



Cocoon of the American Silk Worm. 



Psephenus. 



adhere to the under side of pebbles, and are thoroughly as- 

 similated in color to the mud of streams and the shores of 

 the sea. 



Much light may be thrown upon this subject by a study of 

 cave animals. Here the harmony in color and often in form 

 to surrounding objects is most striking and the causes are 

 quite apparent. The cave insects becoming blind from the 

 darkness of their subterranean abode, lose their colors and 

 are assimilated to the colors of the stalactites on which they 

 walk or the walls of the cave to which they cling. The 

 ground beetles, instead of being dark like their out-of-door 

 relations, here fade out to the color of the limestone sands 

 over which they run. The hurmon}' in form and color with 

 the environments of their subterranean abode is as apparent 

 as tlio cause. 



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