INSECTS IN RELATION TO OTHER ANIMALS 221 



the croppies; while they made a fourth or more of the alimentary con- 

 tents of the sheepshead (forty-six per cent.), the darters, the pirate perch, 

 the common sunfishes (Lepomis and Chcenobryttus), the rock bass, the 

 little pickerel, and the common sucker (thirty-six per cent.). 



"Ephemerid larvas were eaten by two hundred and thirteen specimens 

 of forty-eight species not counting young. The larva of Hexagenia, 

 one of the commonest of the 'river flies,' was by far the most important 

 insect of this group, this alone amounting to about half of all the Neurop- 

 tera eaten. It made nearly one half of the food of the shovel fish, 

 more than one tenth that of the sunfishes, and the principal food resource 

 of half-grown sheepshead; but was 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 tw r elve 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 un- 

 doubtedly vary more or less from year to year, they are here for con- 

 venience 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 albi- 

 pcnnis for the most part, and then caterpillars and various beetles. 

 When the small fruits appear, these are largely eaten instead of insects; 

 thus in June, cherries and raspberries form fifty-five per cent, and insects 



