CHARACTERISTICS OF INSECTS 



477 



Finally the skin splits for the last time, and an adult with full- 

 fledged wings appears. 



The potato beetle is a very destructive insect and causes 

 enormous loss to farmers. The adult has strong jaws with 

 which it bites the leaves of potato vines and destroys the plant. 

 The female lays over 500 eggs a summer, in clusters on the under 

 side of the leaf of the potato plant. The young larvae which 

 hatch from the eggs feast on the leaves for two weeks and some- 

 times strip the vines of all leaves. At the end of the two weeks 

 of this greedy feeding the larvae bury themselves in the earth as 

 pupae and remain there for ten days. Then they leave their 

 pupa skins and appear above ground as adult beetles (Fig. 345). 



The life history of the squash bug is simpler than that of the 

 fly, mosquito, and potato beetle. The eggs of the squash bug 

 hatch into nymphs or young squash bugs which resemble the 

 parent except for size and wings ; but the eggs of the fly and 

 beetle hatch into larvae which are totally 

 unlike the parent, and which must pass 

 through a pupa stage before they become 

 adults like the parent. Some larvae, like 

 the fly and mosquito larvae, have no protec- 

 tion during the pupa period except their last 

 larva skin ; others, like silk moth larvae, spin 

 cocoons or build cases in which to pass the 

 pupa stage ; the caddis fly larva, for example, 

 builds a case of mud and stones in which 

 it rests during its change or metamorphosis 

 to an adult fly. 



Characteristics of insects. At first sight there seems little 

 similarity between a potato beetle, a butterfly, a roach, a clothes 

 moth, and a grasshopper. But all of these animals are classed 

 as insects because in their adult form they have certain definite 

 characteristics in common. All have three distinct regions to 



