94 AMERICAN HOME GAEDEX. 



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CHAPTER IX. 



Insects; general Characteristics of ; Changes of ; Prevalence of. — Means of 

 Defense and Offense against them. 



INSECTS. 



IxsECTS, in general, complete the roiind of their life, or rath- 

 er lives, in one year. There are some exceptions, however, as 

 the well-knoT\-n seventeen-yeax locust, and also some three and 

 four year insects, as the saperda, the May-bug, and the spring 

 beetle or snapper, parents of the apple-tree borer, the corn- 

 grub, and the wire-T^'onn. But, "whether the period in which 

 their changes occm- be short or long, they are all definitely ef- 

 fected. The young are hatched, or the insect wakes from its 

 torpor at the time of the opening of the leaves or flowers vipon 

 which they have to feed ; and if, from any cause, they hatch 

 before their food is ready, they die, although this rarely, if ever, 

 happens. 



They are air-breathers, with varied apparatus for this pur- 

 pose suited to their condition, and changing with it. In the 

 larva, or worm state, they are commonly fm'nished with spir- 

 acles or breathing-holes along their sides. 



Their digestive apparatus consists, as in the snipe or wood- 

 cock, of a single maiform tube. In its passage through this 

 simple opening, their food is elaborated, and the colorless blood 

 formed. This, in their system of circulation, is carried with 

 regularity from tail to head, and back again, passing in its re- 

 turn through the respiratory tubes. While in the larva or worm 

 state, they are voracious and generally injurious. They eat, 

 and digest, and spin through their allotted time, all the indi- 

 viduals of the same kind ha\-ing equal life, however varied the 

 limit of life in this condition may be in the different species. 

 At the close of this definite period they take the chrysalis form, 

 changing their appearance, structm-e, and mode of existence. 



Having completed their organization and growth in the 



