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 



