BIRDS, CATERPILLARS, AND PLANT LICE. 



121 



Fig. 40. — Cateriiillar of tlie white niarkeil tussock 

 niotli, a destructive shade-tree pest, eaten hy many 

 liirds. 



country from injury by these insect.s is largely due to the 

 good work of natiye birds, while the greater destructiveness 

 of this insect in our cities is no doubt in oonseijuence of (he 

 scarcity of such Ijirds there. 



Regarding the immunity of brightly colored caterpillars 

 from destruction l)y birds, my evidence is mainly of a nega- 

 tiye character, and 

 therefore of little 

 value. I have never 

 known birds to eat 

 certain of the most 

 gaudily colored cater- 

 pillars, while others 

 are commonly eaten 

 by them. It would 

 seem that such larvte 

 as are made conspicuous by their coloring must have some 

 means of protection against their enemies. In some instances 

 these bright colors ma}' serve to warn birds that the creature 

 displaying them is distasteful or unfit for food. Usually, 

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

 fore, be pre^'ed upon hy natural enemies. 



In that most adnural)le local economic study of liird 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 l)y birds 

 has been mentioned in the notes on the pea })laiit louse" 

 (p. 'i'i)^. I cannot understand how Dr. Judd could have 

 been led into making such erroneous statements, for the 

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

 ignored l)y 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 cal)bage 

 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 Avinter 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- 



