64 THE MEANING OF EVOLUTION 
it was with greatest delight that Philadelphia heard of 
the new birds which ate the pest. One wonders why 
some ornithologist did not look at the bird long 
enough to see that it had the sort of a bill character- 
istic of birds that eat seeds. It is true that most birds 
feed their young on insects, hence there is a time when 
any bird is apt to be insectivorous. But the structure 
of the sparrow’s bill, like that of all finches, should 
have warned these bird-lovers that the sparrow was 
not to be depended upon to earn his living by catching 
worms. It is easy, however, to be wise after the 
event. Philadelphia believed she was engaging in a 
particularly advanced movement when she imported 
from England one thousand English sparrows, nearly 
as many as were liberated by all other cities together. 
These birds were turned loose among the shady streets 
and wide spreading parks of the City of Brotherly 
Love. 
It is a serious matter lightly to disturb the balance 
of nature by the introduction of a new species. It is 
true that the sparrow did eat some spanworms and 
for a while enthusiastic bird-lovers hoped that here 
was the solution of the difficulty. Philadelphians will 
also remember that, with the spanworm removed from 
competition, the tussock moth, whose caterpillar car- 
ries on his back a series of yellow, red, and black 
paint brushes, at once become the permanent parasite 
