296 ENTOMOLOGY 



head. But we should not therefrom derive the general, but 

 false and mischievous notion 'that the indefinite multiplication 

 of either birds or predaceous insects is good. Too many of 

 either is nearly or quite as harmful as too few. 



" There is a general consent that primeval nature, as in the 

 uninhabited forest or the untilled plain, presents a settled har- 

 mony of interaction among organic groups which is in strong 

 contrast with the many serious mal-adjustments of plants and 

 animals found in countries occupied by man. 



' To man, as to nature at large, the question of adjustment 

 is of vast importance, since the eminently destructive species 

 are the widely oscillating ones. Those insects which are well 

 adjusted to their environments, organic and inorganic, are 

 either harmless or inflict but moderate injury (our ordinary 

 crickets and grasshoppers are examples) ; while those that are 

 imperfectly adjusted, whose numbers are, therefore, subject 

 to wide fluctuations, like the Colorado grasshopper, the 

 chinch-bug and the army worm, are the enemies which we 

 have reason to dread. Man should then especially address 

 his efforts, first, to prevent any unnecessary disturbance of the 

 settled order of the life of his region which will convert rela- 

 tively stationary species into widely oscillating ones; second, 

 to destroy or render stationary all the oscillating species in- 

 jurious to him; or, failing in this, to restrict their oscillations 

 within the narrowest limits possible. 



" For example, remembering that every species oscillates to 

 some extent, and is held to relatively constant numbers by the 

 joint action of several restraining forces, we see that the re- 

 moval or weakening of any check or barrier is sufficient to 

 widen and intensify this dangerous oscillation ; may even con- 

 vert a perfectly harmless species into a frightful pest. Wit- 

 ness the maple bark louse, which is so rare in natural forests 

 as, scarcely ever to be seen, limited there as it is by its feeble 

 locomotive power and the scattered situation of the trees it 

 infests. With the multiplication and concentration of its food 

 in towns, it has increased enormously, and, if it has not done 



