BIRDS, CATERPILLARS, AND PLANT LICE. 121 



country from injury by these insects is largely due to the 

 good work of native birds, while the greater destructiveness 

 of this insect in our cities is no doubt in consequence of the 

 scarcity of such birds there. 



Eegarding the immunity of brightly colored caterpillars 

 from destruction by birds, my evidence is mainly of a nega- 

 tive character, and 

 therefore of little 

 value. I have never 

 known birds to eat 

 certain of tlie most 

 gaudily colored cater- 

 pillars, while others 

 are commonly eaten ^, ,„ „. ... 



•> Fig. 40. — Caterpillar of the white-miirked tussock 



by them. It would moth, a destructive shade-tree pest, eaten by many 



seem that such larvfe 



as are made conspicuous by their coloring must have some 

 means of protection against their enemies. In some instances 

 these bright colors may serve to warn birds that the creature 

 displaying them is distasteful or unfit for food. Usually, 

 however, such caterpillars are not numerous, and must, there- 

 fore, be preyed upon by natural enemies. 



In that most admirable local economic study of bird life 

 by Dr. Judd, " The Birds of a Maryland Farm," we find the 

 following statements : "The pea plant louse is a new species, 

 unfamiliar to birds, which, however, seldom eat plant lice" 

 (p. 28) ; "The fact that plant lice are not selected by birds 

 has been mentioned in the notes on the pea plant louse" 

 (p. 29). I cannot understand how Dr. Judd could have 

 been led into making such erroneous statements, for the 

 facts are that, Avhile some species of plant lice appear to be 

 ignored by birds, other species often form for them a staple 

 food supply. For example, I have never seen any bird eat 

 the melon plant louse, but several species eat the cabbage 

 plant louse, and the birch aphis is a favorite food for birds. 

 It is also a well-known and undisputed fact that some birds 

 subsist largely during the winter on the eggs of plant lice. 

 Before Dr. Judd's paper was given to the public, several in- 

 vestigators had published the fact that certain birds eat cer- 



