152 A BOOK OF INSECTS 



with which they associate rely for protection upon the 

 unusual hardness of their integuments. They are prob- 

 ably perfectly edible ; but the smaller insectivorous 

 birds are unable to feed upon them because they cannot 

 pierce their armour. Some hard beetles and their mimics 

 are almost identical in appearance ; yet the one specimen 

 would need a smart blow from a hammer to destroy it, 

 while the other might be crushed between the finger and 

 thumb. We see, therefore, that the association of inedible 

 qualities with warning colours does not constitute the 

 only model for mimicry. Sometimes a distinctive char- 

 acteristic is copied, or a striking habit. For example, 

 leaf-cutting ants are common in certain parts of tropical 

 South America. They may be seen in countless numbers 

 passing to and fro along their runs ; and each homeward- 

 bound ant carries a piece of green leaf, about the size of a 

 sixpence, in its jaw. Not only the appearance of the ant 

 itself, but also the semblance of the piece of leaf, are 

 reproduced in the person of an inoffensive plant-bug ; and 

 there seems no room for doubt that this insect shares in 

 the immunity from attack enjoyed by the leaf-cutting 

 ants, which are avoided because of their fierce, warlike 

 nature. 



The most striking examples of insect mimicry are 

 found among tropical Lepidoptera. When the naturalist 

 Bates returned from his travels in South America he 

 brought with him a large collection of butterflies, among 

 which were some that he had placed together, believing 

 them to be of the same species. Closer inspection revealed 

 the astonishing fact that the supposed identity was only 

 superficial ; that species belonging to distinct families 

 were so much alike in shape, colour, and markings as to 

 be absolutely indistinguishable when on the wing. The 

 full significance of this discovery cannot be grasped by 



