314 ILLINOIS STATE HORTICULTURAL SOCIETY. 



It would be interesting, did time permit, to compare with the in- 

 efificacy of birds in combatting some of the more prolific and injurious 

 species of insects, the extensive destruction of many of these species by 

 the natural enemies in their own class, and especially by the parasitic 

 insects. These creatures are so minute that to all ordinary observation 

 they may be said to be invisible, and therefore their agency is almost 

 unknown, except to professed entomologists, and even they have prob- 

 ably as yet formed no adequate conception of the extent of their oper- 

 ations. But there are many cases on record where some destructive 

 insect has suddenly disappeared without obvious cause, and upon ex- 

 amination every remnant of them is found to be infested by one or 

 more of these internal parasites. But these, also, have their preferences 

 in the selection of their foster-parents, and seem to be especially addicted 

 to the larvae of the Lepidoptera. Striking instances have been known 

 of the wholesale destruction of the army worm, the tent caterpillar of 

 the forest, and the larvje of the tussock moth in this manner. But there 

 are some of our most destructive insects, of which the chinch bug is a 

 notorious example, which are almost completely exempt from damage 

 by natural enemies of any kind, and the only sure remedy which is some- 

 times left to us in such cases is the final one of abandoning for a time 

 the crops upon which they chiefly subsist. 



Here, too, would be the proper place to introduce a consideration of 

 a question which has been sometiines raised, whether birds may not do a 

 great deal of harm by destroying indiscriminately the beneficial insects, 

 both predaceous and parasitic. The argument is this : that many of the 

 insects destroyed by birds are infested by internal parasites, often many 

 in number, each one of which, when arrived at maturity, would be instru- 

 mental in destroying many more, and therefore that in devouring these 

 infested individuals, birds destroy many more of our friends than of our 

 enemies. This, like many other plausible arguments, shows its own fal- 

 lacy by proving too much. If birds do more harm than good by destroy- 

 ing parasitized insects, then so do we, and we should abstain from killing 

 all kinds of noxious insects for the same reason. This position assumes 

 that the class of insects contains within itself a sufficient system of checks 

 and balances to keep its species within proper bounds; and if the argu- 

 ment be made of general application, it excludes the whole series of 

 insectivorous birds from any normal or useful part in the economy of 

 nature. 



It would also be an interesting inquiry respecting the different 

 classes of agents for keeping insects in check, namely, the insectivorous 

 birds, the predaceous insects, and the parasitic insects, whether they 

 occupy, to any considerable extent, different and distinct fields of oper- 

 ation, and whether, therefore, the work of one class may be said to be the 

 complement of that of the others. That this is true to a certain extent 

 there can be no doubt, but to how great an extent, it would require much 

 time and investigation to determine. The following statements may help 

 to elucidate the subject. 



