CHAPTER VII. 



THE RELATIONS OF BIRDS TO r'REDACEOUS AND IWRASITIC 



INSECTS. 



The attempt is frequently made (o ])elittle the usefulness 

 of birds by tlie argument that they do as nuu-li harm l)y feed- 

 ing upon predaeeous 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 (jf an injurious insect. 



(3) The primary parasite of an insect feeding on a no.xious 

 plant. 



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

 ious plant. 



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

 plant of no economic value. 



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

 plant of no economic value. 



(7) The primary parasite of a j)redaceous insect. 



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