6o TRANSACTIONS OF THE ILLINOIS 



summers had passed we would have no more destruction by noxious 

 insects than we had during the season just passed, and that the chances 

 are at least even that there would be fewer insects the fifth season after 

 the birds were all destroyed than there were before. Why ? Simply for 

 the reason that the great destroyers of insect-life are insects themselves, 

 and though the birds destroy myriads, their effect on the great mass 

 practically amounts to but very little ; and besides, the birds generally 

 destroy at least as many beneficial parasitic insects as they do noxious, 

 and I will only qualify this seemingly rash assertion by saying that they 

 destroy more beneficial insects than they do of those that are known 

 to us as noxious ; yet, it is also a fact that some birds keep in entire 

 subjection certain classes of insects that would be extremely noxious were 

 it not for the birds ; but the swallow, the swift and the night-hawk, as 

 they flash through the air of an evening, may, and do, in a kw moments 

 overbalance the good work of all other birds combined during the day, 

 by gathering to their destruction in their carnivorous mouths the tiny 

 parasitic gnats that swarm in their love-flights through the air ; each and 

 every pair of these gnats, so destroyed, was capable of the destruction of 

 fifty to two hundred and fifty ravCnous caterpillars or other noxious 

 larvae. The orchardist who with intense satisfaction watches the visits of 

 the Baltimore oriole to the nest of the tent-caterpillar in his apple-tree, 

 at each visit carrying ofl" a grub, becomes disgusted when on investigation 

 he finds that the oriole is only rendering the existence of this noxious 

 caterpillar possible by tearing the captured grubs open and taking from 

 their bodies the grub of a parasitic ichneumon fly that had a foreclosed 

 trust-deed on the caterpillar's life. But strange as it may appear, the 

 oriole is doing a double duty, he is not only rendering it possible for 

 the caterpillar to increase and multiply his species, but the ichneumon 

 a,s well, for if he did not thin out and decimate the fly it would soon 

 entirely destroy the tent-caterpillar race, and then it would necessarily 

 cease to exist for want of its proper food ; but it is not possible for such 

 catastrophies to happen unless the wheel of Nature is badly obstructed. 

 The more we study this great law of "eat and be eaten," the greater our 

 astonishment becomes at the vast and intricate system of checks and 

 counter-checks in all life. The entire dependence of the life of one 

 species on that of another has led some naturalists to believe and assert 

 that the entire destruction of a certain species would destroy the harmony 

 of Nature and bring about almost chaotic results. But I think there is no 

 fear of such results, were one, ten or a hundred species of life completely 

 destroyed, for each void place in Nature is covered from ten thousand 

 different points, and is instantly occupied, and the disappearance, the 

 sudden destruction of even a prominent species would, it seems to me, 

 be like the casting of a pebble on the surface of a glassy lake ; it would 

 only cause a slight disturbance, possibly wide-spread, but soon quieting, 

 with ilo appreciable effect on the great mass of life, good or bad. 



Another great and general mistake made in this relation is this, that 

 because birds of a certain species are entirely insectivorous they are 

 necessarily the particular ones that are the most beneficial. This is far 



