10 USEFUL BIRDS. 
when insect food is not plentiful, and so be ready to check 
any increase of insects which may occur. On the other 
hand, if they become too numerous, they may create serious 
disturbances by destroying grass, grain, or fruit. I have 
witnessed attacks made by certain of these beetles on grain 
and strawberries; and were they not held in check by 
birds, it is probable that they would soon become serious 
pests. Their destruction by Robins and other birds tends 
to keep these beetles within those normal bounds where 
they will do most good and least harm; while the check 
kept by the Crow on the increase of the Robin may pre- 
vent the latter from destroying too many ground beetles. 
If certain low-feeding caterpillars became so numerous as to 
be injurious, ground beetles and Robins would feed largely 
on them. The caterpillars would then largely take the place 
of the beetles in the Robin’s food. The beetles, therefore, 
would increase in numbers, and the force of both bird and 
beetle would be exerted to reduce the caterpillars to their 
normal limit. This accomplished, the Robin would again 
attack the ground beetles, and thus tend to reduce them 
to normal numbers. 
Let us now go back to the beginning of our chain of 
destruction. The Eagles, Hawks, Owls; and raccoons may 
indirectly allow an increase in the number of Robins by 
preventing too great an increase of the Crow. But Hawks 
and Owls also prey on the Robin, and, by dividing their 
attention between Robin and Crow, assist in keeping both 
birds to their normal numbers. Whenever Crows became 
rare, Robins as a consequence would become very numerous, 
were it not that the Hawks also eat Robins. (Hawks and 
Owls eat also some species of insects that are eaten by both 
Robin and Crow.) 
There are compensations in the apparently destructive 
career of the Crow. An omnivorous bird, it seems inclined 
to turn its attention to any food which is plentiful and readily 
obtained. It is a great feeder on May beetles (miscalled 
“June bugs”), the larve of which, known as white grubs, 
burrowing in the ground, sometimes devastate grass lands 
and also injure the roots of many plants, including trees. 
