452 
ECONOMIC RELATIONS OF OUR BIRDS. 
spiders, during tlieir larval stages. In the adult stages they are found in the 
water and are there occasionally picked up by Sui];)es. 
Considering some of the effects of *entozoa in man in connection with Dr. 
Leidy’s statement that “ their (Gordii) bulk and weight are frequently gi’eater 
than all the soft parts, including the muscles, of tlieir living habitation; never¬ 
theless, with this relatively immense mass of parasites, the insects jump about 
almost as freely as those not infested,’’ there may be a chance for error in decid¬ 
ing just which species of these worms are beneficial and which are detrimental. 
If, in the case of the gi'asshoppers, the parasites do not kill their hosts nor pre¬ 
vent them from laying perfect eggs, they must be classed as detrimental, for 
their presence in the insect must have the effect of increasing the amount of 
food consumed by it. It amounts to the same thing as hair-worms eating vegeta¬ 
tion; but the reverse of this would be true of species infesting spidem, for they 
would be required to kill more insects than if not infested. 
It will be observed that in the foregoing classification nothing has been said of 
what are commonly known as “neutral” plants and “neutral ” insects. Not¬ 
withstanding such statements as ^ “ Birds destroy insects enormously, but these 
are in the gi-eat part neutral,” it is doubtful if any such insects exist,-at least 
when life is considered in its broadest relations to man. What noxious insect 
or plant have we which, wRen judged by the usual standard of neutrality, was 
not once neutral? Nineteen years ago the Colorado potato beetle, feeding in its 
original habitat upon a wild species of Solarium, would have been classed as 
neutral, and yet it only needed the encroachment of civilization upon its home 
to enable it to march eastward and take possession of the whole potato gi’owing 
region of the United States, which it now holds with a tenacity that baffles all 
opposition. There are now feeding upon the potato beetle between twenty-five 
and thirty insects, all of which, until their j)os&ibilities of usefulness became 
known, would have been classed with the beetle upon which they prey as 
neutral. Now they are acknowledged friends, while the beetle is a pronounced 
enemy. All those insects which may feed upon plants under cultivation, or 
upon those which are yet to come under cultivation, are, with the utmost 
consideration for them, to be looked upon as but latent enemies, and guarded 
as such, while those animals which hold them in check should be looked upon 
as latent allies, to be held in reserve for future needs. But when vegetation 
not under cultivation, and not to be regarded as weeds, is considered with refer¬ 
ence to its soil-producing function, to its influence upon climate, and to the 
production of lumber and fuel, the insects which feed upon it are injurious, and 
the birds and insects which hold them in check are beneficial. Viewed in this 
light, the life of the Rocky Mountains and that of the wilds of the British 
Possessions are as directly connected with human interests as the winds and the 
waters which flow from them. The food of birds cannot, therefore, be said to 
consist of insects which are, in the great part, neutral. 
When it is proposed to utilize birds as insect destroyers, to increase the abun¬ 
dance of certain species and to exterminate or hold in check others, to encourage 
the breeding of certain birds in given places and to prevent others from doing 
so; or, when it is jDroposed to introduce into a countiy a foreign species, other 
questions than those of food simply must be considered. 
Some of the more important of these are the following: 
(1) The relations which the bird holds to dijferent industries. The failure to 
recognize the dissimilar relations which various birds sustain to different indus- 
> Nature's Jleans of Limiting the Number of Insects. Aih. Nat,, Vol, VIII, p. 270, 
