INSECTS IN RELATION TO OTHER ANIMALS 225 



geese , ducks, gulls and pelicans came to share in the feast. Aughey 

 estimated that the locusts eaten in one day by the passerine birds of the 

 eastern half of Nebraska were sufficient to destroy in a single day 174,397 

 tons of crops, valued at $1,743.97. 



Weed and Dearborn state that, of Hemiptera, Jassidae are very often 

 found in the stomachs of birds, and that aphids and their eggs~form a 

 large part of the food of many of the smaller birds, such as the warblers, 

 nuthatches, kinglets and chickadees. "A large proportion of the cater- 

 pillars of the Lepidoptera are eagerly devoured by birds, forming an 

 important element of the food of many species. The hairy caterpillars 

 are eaten by cuckoos and blue-jays and the large saturniid caterpillars, 

 such as cecropia and polyphemus, by some of the hawks. Almost all 

 kinds of Coleoptera are food for birds, but especially the grubs of Scara- 

 baeidae, which are eagerly devoured by robins, blackbirds, crows and 

 other birds. Of the Diptera, Cecidomyiidae and other gnats are eaten 

 by swallows, swifts and night hawks; while Tipulidae are often found in 

 the stomachs of birds. Among Hymenoptera, ants are eaten exten- 

 sively by woodpeckers, catbirds and many other species, as are also 

 Ichneumonidae and other parasitic forms these last by the flycatchers 

 in particular. 



The Regulative Action of Birds upon Insect Oscillations. 

 The worst injuries by insects are done by species that fluctuate exces- 

 sively in number as the result of variations in those manifold forces that 

 act as checks upon the multiplication of the species. 



In order to determine whether birds do anything to reduce existing 

 oscillations of injurious insects, Professor Forbes made some admirable 

 studies upon the food of birds which were shot in an Illinois apple or- 

 chard which was being ravaged by canker-worms. In this orchard, 

 birds were present in extraordinary number and variety, there being at 

 least thirty-five species, most of which were studied by Forbes, from 

 whose exhaustive tables the following food-percentages are taken: 



Birds Examined. Insects. Canker-worms. 



Robin, 9 93% 21% 



Catbird, 14 98 15 



Brown Thrush, 4 94 12 



Bluebird, 5 98 12 



Black-capped Chickadee, 100 61 



House Wren, 5 91 46 



Tennessee Warbler, i 100 80 



Summer Yellow Bird, 5 94 67 



Black-throated Green Warbler, .... i 100 70 



Maryland Yellow-throat, 2 100 37 



Baltimore Oriole, 3 100 40 



16 



