18 



EXTERNAL STRUCTURE OF INSECTS 



locusts, which we commonly call grasshoppers (Fig. 19), the true 

 grasshoppers (Fig. 20), and katydids (Fig. 21); crickets, "walking- 

 sticks" (Fig. 22), and cockroaches. These insects have, for the 

 most part, four wings, the foremost pair being really wing covers, 

 or tegmina; the second pair are thin and gauzy, the mouth parts 

 are formed for biting, and the metamorphosis is incomplete. The 



FIG. 16. Earwig with wings FIG. 17. Upper figure, fe- 



expanded. male earwig; below, end of 



abdomen of male, showing 



appendages. Both much 



enlarged. 



FIG. 



18. A specimen 

 thrips. 



of 



grasshoppers, locusts, crickets and katydids have hind legs adapted 

 for jumping. This order is at times very injurious; the Rocky 

 Mountain locust or grasshopper, which normally lays its eggs on 

 the slopes of the Rockies, frequently breeds on the plains east of 

 there, and has at times swept down upon portions of Kansas, 

 Nebraska, Dakota, Minnesota and other states, leaving no living 



