ECONOMIC RELATIONS OF OUR BIRDS. 
451 
How far birds are destructive to parasitic insects cannot be stated with cer¬ 
tainty at present. The fact, however, that the contents of not more than 
thirty-two out of six hundred stomachs, examined carefully under the micro¬ 
scope, gave any evidence of parasitic hymenoptera, and that, if we set aside the 
probably exceptional case of the Pewee, already mentioned, usually but one, or 
occasionally two of these insects were found in a stomach, indicates that this 
group of parasites is not preyed npouby birds to the same extent that other in¬ 
sects are. It should be said, however, that some sixteen species of l:)irds are 
lu'oved to feed upon those insects to some extent, and that these species represent 
Thrushes, Titmice, Warblers, Swallows, Flycatchers and Finches as well as the 
Hummers. Large birds, like the Robin and CheAvink, as Avell as the small 
Kinglets and the Humming Bird, eat these hymenopterous friends. Birds, 
doubtless, destroy large numbers of parasites with the insects which they infest, 
but such a destruction is admissible. 
(7) A bird may be classed as an enemy in so far as it feeds upon beneficial 
predaceous insects, spiders and myriapods. It is in the destruction of these 
forms that we are to apprehend the greatest injury from our birds. They are 
large, conspicuous, and, as a rule, easily captured. They are extremely numer¬ 
ous, and frequent CA^ery situation vUich a bird may visit. The majority of 
them, to obtain food, are obliged to lead roAung lives, and are thus more exposed 
and consequently more liable to be discoA^ered by birds than many of the i^lant- 
eating insects are. In the directness of their effect upon insect life, they take 
the same rank with birds, for wheir they secure their prey its deA’astations are 
at an end. Like birds, too, they feed more or less indiscriminately upon Avhat- 
ever insects they may capture; nor does this trait detract so much from their 
general usefulness as might be expected. It is, in fact, this habit Avhich enables 
them to maintain a somewhat steady abundance even when the caprices of 
climate or an over-abundance of parasites nearly exterminates certain insects 
upon which they commonly feed. A parasitic insect confined to one, or at 
most to but a few, species, must fluctuate in abundance with it, and no matter 
hoAv abundant or how destructive another insect may become, it is poAverless to 
destroy it, or to saA*e itself. With predaceous forms, hoAvever, this case 
is quite different, and their general tendency, like that of birds, is to maintain 
a steady, rather than a A'acillating, abundance. Many of the Avasps, the Tiger 
and Ground beetles, the Lady-birds, a feAv moths (Report of Department of 
Agriculture for 1879), the Asilus and Syrphian flies, many of the true Bugs, the 
Dragon-flies and Lace-wings, nearly all of the Spiders and many of the Myria¬ 
pods, are representatives of this group, and, as Avill be seen beyond, all of them 
are destroyed to a greater or less extent by A^ery many of our birds. 
(8) A bird does us harm when it feeds upon carrion insects. Hoav much of 
health we owe to these scavengers Ave can only imagine, but that they do exert 
a great influence in checking malarial diseases Ave have no reason to doubt. 
Fortunately for us, birds do not appear to be very destructiA’e to these insects, 
especially in their larA'al states. 
(9) A bird is harmf ul when it eats beneficial ivorms. In the light of the in¬ 
vestigations made by Charles Dai'Avin on the “Origin of Vegetable Mould,” 
angle-worms, or earth-AA’orms, appear to render an important service in the ac¬ 
cumulation of this most essential material to the growth of shalloAv-rooted 
vegetation. Not a small number of our birds feed on angle-Avorms to some 
extent. 
Hair-worms (Gordii) and some other similar forms are other members of this 
group, some of w^hich are parasitic on grasshoppei's and other insects, including 
