UTILITY OF BIRDS IN NATURE. 11 
The Crow is also a destroyer of cutworms. These are 
the young or larve of such noctuid moths or “millers” 
as are commonly seen fluttering from the grass by any one 
who disturbs them by walking in the 
fields. Robins also feed largely on Be 
cutworms, as well as on the white Fig. 3.—Cutworm. 
grub of the May beetle. When these insects are few in 
number, a part of the usual food supply of both Robin 
and Crow is cut off. This being the case, the hungry 
Crows are likely to destroy more young 
m Robins and other young birds than 
y usual, in order to make up the supply 
of animal food for themselves and their 
ravenous nestlings. In afew years this 
would decrease perceptibly the number 
of Robins and other small birds, and would be likely in 
turn to allow an increase of May beetles and cutworms. 
As these insects became more plentiful, the Crows would 
naturally turn again to them, paying less attention to the 
young of Robins and other birds for the time, and allowing 
them to increase once more, until their multiplication put 
a check on the insects, when the Crows would of necessity 
again raid the Robins. 
The Blue Jay may be taken as another instance of this 
means of preserving the balance of nature. Hawks and 
Owls kill Blue Jays, Crows destroy their eggs and young ; 
thus the Jays are kept in check. Jays are omnivorous 
feeders. They eat the eggs and young of other birds, par- 
ticularly those of Warblers, Titmice, and Vireos, — birds 
which are active caterpillar hunters. But Jays are also 
extremely efficient caterpillar hunters. Thus the Jays 
compensate in some measure for their destruction of cat- 
erpillar-eating birds, by themselves destroying the cater- 
pillars which they unconsciously have allowed to increase 
in numbers by destroying these birds. Like the Crow, 
they virtually kill the young of the smaller birds, and eat 
them, that they (the Jays) may eventually have more in- 
sect food for their own young. When this object has been 
attained, the Jays may again, perhaps, allow an increase of 
Fig. 4.—Noctuid moth. 
