284 ENTOMOLOGY 



than one tenth that of the sunfishes, and the principal food re- 

 sources of half-grown sheepshead ; but were rarely taken by 

 the sucker family, and made only five per cent, of the food of 

 the catfish group. 



" The various larvae of the dragon flies, on the other hand, 

 were much less frequently encountered. They seemed to be 

 most abundant in the food of the grass pickerel (twenty-five 

 per cent.), and next to that, in the croppie, the pirate perch, 

 and the common perch (ten to thirteen per cent.). 



"Case-worms (Phryganeidae) were somewhat rarely 

 found, rising to fifteen per cent, in the rock bass and twelve 

 per cent, in the minnows of the Hybopsis group, but otherwise 

 averaging from one to six per cent, in less than half of the 

 species." 



Insects in Relation to Birds. From an economic point 

 of view the relations between birds and insects are extremely 

 important, and from a purely scientific standpoint they are no 

 less important, involving as they do biological interactions of 

 remarkable complexity. 



The prevalent popular opinion that birds in general are of 

 inestimable value as destroyers of noxious insects is a correct 

 one, as Dr. Forbes proved, from his precise and extensive 

 studies upon the food of Illinois birds, involving a laborious 

 and difficult examination of the stomach contents of many 

 hundred specimens. All that follows is taken from Forbes, 

 when no other author's name is mentioned, and though the 

 percentages given by Forbes apply to particular years and 

 would undoubtedly vary more or less from year to year, they 

 are here for convenience regarded as representative of any 

 year and are spoken of in the present tense. About two thirds 

 of the food of birds consists of insects. 



Robin. The food of the robin in Illinois, from February to 

 May inclusive, consists almost entirely of insects ; at first, 

 larvae of Bibio albipennis for the most part, and then caterpil- 

 lars and various beetles. When the small fruits appear, these 

 are largely eaten instead of insects ; thus in June, cherries and 



