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. . 
Regarding 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 the most 
gaudily colored cater- 
pillars, while others 
are commonly eaten 
Fig. 40.— Caterpillar of the white-marked tussock 
by them. It would moth, a destructive shade-tree pest, eaten by many 
birds. 
seem that such larve 
as are made conspicuous by their coloring must have some 
means of protection against theirenemies. 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, while 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- 
