INTKODUCTION OF INSECTS. 133 



Int/roduction of Insects. 



The general tendency of man's encroachments upon spontano- 

 ous nature has been to increase insect life at the expense of 

 vegetation and of the smaller quadrupeds and birds. Doubtless 

 there are insects in all woods, but in temperate climates they are 

 comparatively few and harmless, and the most numerous tribes 

 which breed in the forest, or rather in its waters, and indeed in 

 aU soHtudes, are those which Httle injure vegetation, such as mos- 

 quitoes, gnats, and the like. With the plants cultivated by man 

 come the myriad tribes which feed or breed upon them, and 

 agriculture not only introduces new species, but so multipHes the 

 number of individuals as to defy calculation. Newly introduced 

 vegetables frequently escape for years the insect plagues which 

 had infested them in their native habitat ; but the importation of 

 other varieties of the plant, the exchange of seed, or some mere 

 accident, is sure in the long run to carry the Qg^, the larva, or 

 the chrysalis to the most distant shores where the plant assigned 

 to it by nature as its possession had preceded it. Tor many years 

 after the colonization of the United States, few or none of the 

 insects which attack wheat in its different stages of growth, were 

 known in America. During the Revolutionary war, the Hessian 

 fly, Cecidomyia dest/puct/rix, made its appearance, and it was so 

 called because it was first observed in the year when the Hessian 

 troops were brought over, and was popularly supposed to have 

 been accidentally imported by those unwelcome strangers. Other 

 destroyers of cereal grains have since found their way across the 

 Atlantic, and a noxious European aphis has first attacked the 

 American wheat-fields within the last twenty-five or thirty years. 

 Unhappily, in these cases of migration, the natural corrective of 

 excessive multiphcation, the parasitic or voracious enemy of the 

 noxious insect, does not always accompany the wanderings of its 

 prey, and the bane long precedes the antidote. Hence, in the 

 United States, the ravages of imported insects injurious to culti- 

 vated crops, not being checked by the counteracting influences 

 which nature had provided to Hmit their devastations in the Old 

 "World, are more destructive than in Europe. It is not known 

 that the wheat midge is preyed upon in America by any other 

 insect, and in seasons favorable to it, it multiplies to a degree- 



