INSECTS IN RELATION TO OTHER ANIMALS 223 



creeper berries and grapes, these are eaten to the extent of seventy-six 

 per cent., the insect element of the food falling to twenty-one per cent., 

 of which almost half consists of ants, and the remainder of beetles and a 

 few caterpillars. 



For the entire year, as appears from the study of seventy specimens 

 by Forbes, insects form forty-three per cent, of the food of the catbird 

 and fruits fifty-two per cent. As the injurious insects killed are offset 

 by the beneficial ones destroyed, "the injury done in the fruit-garden by 

 these birds remains without compensation unless we shall find it in the 

 food of the young," says Professor Forbes. And this has been found, to 

 the credit of the catbird ; for Weed learned that the food of three nest- 

 lings consisted of insects, sixty-two per cent, of which were cutworms 

 and four per cent, grasshoppers; while Judd found that fourteen nest- 

 lings had eaten but four per cent, of fruit, the diet being chiefly ants, 

 beetles, caterpillars, spiders and grasshoppers. In fact, Weed believes 

 that, on the whole, the benefit received from the catbird is much greater 

 than the harm done, and that its destruction should never be permitted 

 except when necessary in order to save precious crops. 



Bluebird. The excellent reputation which the bluebird bears every- 

 where as an enemy of noxious insects is well deserved. From a study of 

 one hundred and eight Illinois specimens, Forbes finds that seventy- 

 eight per cent, of the food for the year consists of insects, eight per cent. 

 of Arachnida, one per cent, of Julidae and only thirteen per cent, of vege- 

 table matter, edible fruits forming merely one per cent, of the entire food. 

 The insects eaten are mostly caterpillars (chiefly cutworms), Orthoptera 

 (grasshoppers and crickets) and Coleoptera (Carabidae and Scarabaeidae) . 

 Though some of the insects are more or less beneficial to man, such as 

 Carabidae and Ichneumonidae (respectively predaceous and parasitic), 

 the beneficial elements form only twenty-two per cent, of the food for 

 the year, as against forty-nine per cent, of injurious elements, the remain- 

 ing twenty-nine per cent, consisting of neutral elements. The food of 

 the nestlings, according to Judd, is essentially like that of the adults, 

 being "beetles, caterpillars, grasshoppers, spiders and a few snails." 



Other Insectivorous Birds. Weed and Dearborn, from whose 

 excellent work the following notes are taken, find that the common 

 chickadee devours immense numbers of canker-worms, and that more 

 than half its food during winter consists of insects, largely in the form of 

 eggs, including those of the common tent caterpillar (C. americana), 

 the fall web-worm (H. cunea) and particularly plant lice, whose eggs, small 

 as they are, form more than one fifth of the entire food; more than four 

 hundred and fifty of them are sometimes eaten by a single bird in one day, 



