INSECTS IN RELATION TO OTHER ANIMALS 297 



the gravest injury, it is because the trees attacked by it are of 

 comparatively slight economical value, and because it ha^ 

 finally reached new limits which hem it in once more. 



" We are therefore sure that the destruction of any species 

 of insectivorous bird or predaceous insect, is a thing to be 

 done, if at all, only after the fullest acquaintance with the facts. 

 The natural presumptions are nearly all in their favor. It is 

 also certain that the species best worth preserving are the 

 mixed feeders and not those of narrowly restricted dietary 

 (parasites, for instance), that while the destruction of the 

 latter would cause injurious oscillations in the species affected 

 by them, they afford a very uncertain safeguard against the 

 rise of such oscillations. In fact, their undue increase would 

 be finally as dangerous as their diminution. 



" Notwithstanding the strong presumption in favor of the 

 natural system, when we remember that the purposes of man 

 and what, for convenience' sake, we may call the purposes of 

 Nature do not fully harmonize, we find it incredible that, act- 

 ing intelligently, we should not be able to modify existing ar- 

 rangements to our advantage, especially since much of the 

 progress of the race is due to such modifications made in the 

 past. . . . 



" But far the most important general conclusion we have 

 reached is a conviction of the general beneficence of nature, a 

 profound respect for the natural order, a belief that the part 

 of wisdom is essentially that of practical conservatism in deal- 

 ing with the system of things by which we are surrounded." 



Efficiency of Protective Adaptations of Insects. Inter- 

 esting from a scientific point of view are the various adaptations 

 by means of which insects are protected more or less from 

 their bird enemies. Colorational adaptations having been dis- 

 cussed in another chapter, there remain for consideration 

 (i) hairs, (2) stings, (3) odors, flavors and irritants. Most 

 of what follows is from an admirable paper by Dr. Judd, 

 whose data are based upon his examination of the stomach 

 contents of fifteen thousand birds. 



