PROTECTION FROM ENEMIES 



315 



katydids, so numerous in late summer, have a green color 

 and venation of the wings, making them so inconspicuous 

 among the green leaves that the birds seldom detect them 

 unless they move. The walking stick insects resemble so 

 closely the twigs of the trees among which they live that 

 only the acutest vision spies the creatures so long as they re- 

 main motionless. I have known as many as twenty locusts 

 to sit in the grass within the range of distinct human vision 

 and yet be invisible until they were disturbed. Such 

 protective resemblance prevents the birds and other ene- 

 mies from exterminating the species. 



The measuring worms, larva? of geometrid moths, imi- 

 tate so closely the 

 short rough twigs 

 that I have had to 

 touch the suspi- 

 cious object with 

 my hand before I 

 could be quite sure 

 that it was really 

 an animal. Many 

 of the green larvae 

 feeding on green 

 foliage escape the 

 eyes of their pur- 

 suers because of 

 their protective 

 colors. Some of 

 the crabs take on the somber color of the rocks and 

 stones among which they dwell, and sometimes bear on 

 their shells growths of seaweed and hydroids. Spiders 



FlG. 352. The projection on the right is a geometrid 

 larva. Photograph life size. 



