I 480 ] 60 



species wliicli are iujurious to mankind, chiefly by depredating upon 

 valuable cultivated crops, are much more numerous, although consti- 

 tuting but a very small proportion of the whole insect world. It is im- 

 portant to bear in mind that in these destructive operations insects oc- 

 cupy an exceptional or abnormal position, and that we ourselves have 

 been the means of bringing about this state of things, by the excessive 

 cultivation of certain plants, whereby a corresponding increase of cer- 

 tain species of the insects which feed upon them has been induced. It 

 is very rarely that any such loss of balance between the insect and the 

 vegetable worlds takes place in the state of nature ; and yet, such oc- 

 currences are not wholly unknown. This has happened most remarkably 

 in the case of wood-eating insects, there being instances on record in 

 which extensive tracts of forest trees have been destroyed by the larv.T 

 of some of the more minute wood-boring beetles. 



But, as just stated, it is in their depredations upon some one or other 

 of the more valuable cultivated crops that insects have come into the 

 most direct and serious conflict with human interest. These depreda- 

 tions, as is well known, have often been of a most extensive and ruinous 

 character, causing the annual loss of crops to the value of many milhons 

 of dollars, and in some seasons and localities, necessitating the total 

 abandonment of some of the most valuable and staple productions, 

 such as wheat, barley and potatoes, and also some of our choicest fruits, 

 such as the plum and the peach ; and sometimes threatening the destruc- 

 tion even of the most valuable fruit of all — the hardy and widely dis- 

 tributed apple. These destructive operations of insects have necessarily 

 attracted to them the most earnest attention of both practical and 

 scientific men, and many valuable treatises and reports have been written 

 which have been devoted chiefly to the practical treatment of the sub- 

 ject. It is our present intention to treat of insects from a more general 

 and comprehensive point of view. 



GENERAL UTILITY OF INSECTS. 



From what has just been said, it is evident that it is in the nature of 

 tlieir food and their food-taking habits, that insects hold the closest 

 relationship to human interests ; and this is true not only in the direct 

 manner above described, but also indirectly, by means of the important 

 parts which they fulfill in the economy of nature. Indeed, the opera- 

 tions of insects in this last respect are of such vast importance, that it 

 would be safe to say that if these should cease, the earth would soon be- 

 come uninhabitable by mankind. These operations consist chiefly, first, 

 in the destruction of other insects by the predaceous and parasitic kinds, 

 whereby the excessive increase of the former is held in check ; secondly, 



