230 ENTOMOLOGY 



" Against the uprising of inordinate numbers of insects, commonly 

 harmless but capable of becoming temporarily injurious, the most valu- 

 able and reliable protection is undoubtedly afforded by those predaceous 

 birds and insects which eat a mixed food, so that in the absence or diminu- 

 tion of any one element of their food, their own numbers are not seriously 

 affected. Resorting, then, to other food supplies, they are found ready, 

 on occasion, for immediate and overwhelming attack against any threat- 

 ening foe. Especially does the wonderful locomotive power of birds, 

 enabling them to escape scarcity in one region which might otherwise 

 decimate them, by simply passing to another more favorable one, with- 

 out the loss of a life, fit them, above all other animals and agencies, to 

 arrest disorder at the start, to head off aspiring and destructive rebel- 

 lion before it has had time fairly to make 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 unin- 

 habited forest or the un tilled plain, presents a settled harmony of inter- 

 action among organic groups which is in strong contrast with the many 

 serious mal-adjustments of plants and animals found in countries occu- 

 pied 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 oscil- 

 lating ones. Those insects which are well adjusted to their environ- 

 ments, 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, sub- 

 ject 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 relatively stationary species into widely ocsillating 

 ones; second, to destroy or render stationary all the oscillating species 

 injurious 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 removal or weakening of any 

 check or barrier is sufficient to widen and intensify this dangerous oscil- 

 lation; may even convert a perfectly harmless species into a frightful 



