INSECTS 



231 



ness. Frequent mention has been made of damage wrought by 

 them in the early history of this country. In recent times, the 

 damage has been appalling, especially in the central West. In 

 1874-1876 the damage to crops by the Rocky Mountain locust 

 has been estimated at $200,000,000. At certain times, these 

 locusts migrate from Colorado, Wyoming, and Dakota, where they 

 breed during the summer, and descend in countless millions upon 

 the grain fields to the eastward. Fortunately these invasions 

 have been rare. 



Relatives of the Locust. — One member of this group that we 

 associate with the grasshopper is the cricket. In structure and 

 life habits it resembles the locust. Crickets live most of the 

 time under logs or stones, and seem to prefer darkness to light. 

 The cheerful chirp of the male house cricket is made by rubbing 

 the thickened edge of one wing against a rasplike projection on the 

 opposite wing. The rate of the 

 chirp seems to depend upon 

 the temperature of the sur- 

 rounding air. Another musi- 

 cian known to all is the katy- 

 did. This insect, with its green 

 body and wings, can scarcely 

 be distinguished from the 

 leaves on which it rests. This 

 affords the katydid immunity 

 from attack by many enemies. 

 The protection thus received 

 illustrates what is called protec- 

 tive resemblance. The walking 

 stick, which resembles the 

 twigs on which it is found, 

 and the walking leaf insect 

 of the tropics, are other ex- 

 amples of protective resem- 

 blance. 



The mantis, shown in the illustration on the following page, is 

 provided with strongly built forelegs, with which it seizes and 



The walking stick on twig, showing protective 

 resemblance. 



