CHAPTER VII. 



THE RELATIONS OF BIRDS TO PREDACEOUS AND PARASITIC 



INSECTS. 



THE attempt is frequently made to belittle the usefulness 

 of birds by the argument that they do as much harm by feed- 

 ing upon predaceous and parasitic insects as they do good by 

 devouring the injurious ones. For example, B. D. Walsh, 

 the first State Entomologist of Illinois, claimed that a bird 

 must eat at least thirty injurious insects for every beneficial 

 one in order to be of economic value ; and since then similar 

 arguments have frequently been used. During the last few 

 years students of bird food have commonly placed the results 

 of their studies under these headings : " Beneficial," " In- 

 jurious," "Neutral ;" including in the former all parasitic and 

 predaceous insects. Before proceeding to a general discussion 

 of the principles which underlie this whole subject, the ab- 

 surdity of this assumption may easily be shown. Suppose 

 an ichneumon parasite is found in the stomach of a robin or 

 other bird : it may belong to any one of the following cate- 

 gories : 



(1) The primary parasite of an injurious insect. 



(2) The secondary parasite of an injurious insect. 



(3) The primary parasite of an insect feeding on a noxious 

 plant. 



(4) The secondary parasite of an insect feeding on a nox- 

 ious plant. 



(5) The primary parasite of an insect feeding on a wild 

 plant of no economic value. 



(6) The secondary parasite of an insect feeding on a wild 

 plant of no economic value. 



(7) The primary parasite of a predaceous insect. 



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