200 ENTOMOLOGY 
7 
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, 1f it has not done 
