158 The Food of Bhds. 



and disappear before these delicate but yielding skins. 

 Secondly, while our knowledge of the food of Arctians, 

 cutw^orms and grasshoppers is sufficiently definite and full 

 to enable us to predict with certainty exactly what would 

 happen if those eaten by bluebirds were allowed to live 

 and multiply, we have not the same complete and certain 

 knowledge of the food habits of the different genera of 

 Ichneumonida?, the ground-beetles, the soldier-bugs and 

 soldier-beetles. 



One hundred bluebirds, at thirty insects each day, would 

 eat in eight months about 670,000 insects. If this number 

 of birds were destroyed, the result would be the preserva- 

 tion, on the area supervised by them, of about 70,000 moths 

 and caterpillars (80,000 of them cutworms), 12,000 leaf- 

 chafers, 10,000 curculios and 65,000 crickets, locusts and 

 grasshoppers. How this frightful horde of marauders 

 would busy itself if left undisturbed, no one can doubt. 

 It would eat grass and clover and corn and cabbage, inflict- 

 ing an immense injury itself, and leaving a progeny which 

 would multiply that injury indefinitely. On the other 

 hand, would the 160,000 predaceous beetles and bugs, 

 spiders and ichneumons either prevent or compensate these 

 injuries? I do not believe that we can say positively 

 whether they would or not. 



In a discussion of the natural checks upon the cutworms 

 Professor Riley, in his First Report as State Entomologist of 

 Missouri, mentions two species of Ichneumon that para- 

 sitize the larva, credits the spined soldier-bug and the Oar- 

 abid larva, Calosoma calidtun^ with its destruction, and 

 says that some kinds of spiders are known to prey upon it. 



From the Report of the United States Entomological 

 Commission for 1877, we learn that the grasshopper is 

 preyed upon at one or the other stage by Agonoderus, Har- 

 palus, Amara and other Oarabids ; by soldier-beetles, sol- 

 dier-bugs and spiders ; and that certain Ichneumonidae 

 parasitize the egg. It seems prohahle^ therefore, that the 

 beneficial insects eaten by bluebirds include the special 

 enemies of the cutworms and grasshoppers it destroys ; 

 but he who knows best the small number of reliable ob- 

 servations upon which our general statements of the food 



