412 



EVOLUTION AND ANIMAL LIFE 



or spanworms, are twiglike in appearance, and have the habit, 

 when disturbed, of standing out stiffly from the twig or branch 

 upon which they rest, so as to resemble in position as well as 

 in color and markings a short or a broken twig. One of the 



Fig. 254. — The walking-stick insect, 

 Diapheromera femorata, on twig. 



Fig. 255. — A twig-simulating 

 insect from Samoa. (From 

 specimen.) 



most striking resemblances of this sort is show^n by the large 

 geometrid larva illustrated in Fig. 253, which was found near 

 Ithaca, New York. The body of this caterpillar has a few small, 

 irregular spots or humps, resembling very closely the scars left 

 by fallen buds or twigs. These caterpillars have a special mus- 

 Qular development to enable them to hold themselves rigidly 



