18 INSECTS m GENERAL. 



species which are injurious to manltiud, 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 remark- 

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

 in which extensive tracts of forest trees have been destroyed by the 

 larvjB 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 tha^ insects have (;ome into 

 the most direct and serious conflict wjth human interest. These depre- 

 dations, as is well known, have often been of a most extensive and ruin- 

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

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

 total abaiulonment of some of the most valuable and staple produc- 

 tions, such as wheat, barley and potatoes, and also some of our <;hoicest 

 fruits, such as the plum and the peach ; ami sometimes threatening the 

 destruction even of the most valuable fruit of all — the hardy and widely 

 distributed apple. These destructive operations of insects have neces- 

 sarily 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 subject. It is our present intention to treat of insects from a more 

 general and comprehensive point of .view. 



GENERAL UTILITY OP INSECTS. 



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

 their 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 inji)ortance, that it 

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

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

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

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



