10 
THE RELATION OF 8PARHOW8 To AGRICULTURE. 
Fk.. 5.— Ichneumon fly (after Howard; 
Division of Entomology). 
loaned by 
and although some (of the genus Zjasius), and perhaps others, pos- 
Bess certain injurious traits, while a few may have trails thai are 
beneficial, yel tin- effects in any evenl arc of minor importance; 
so thai ants as a whole may safely be classed as neutral. Spiders, 
which for purposes of convenience arc here classed with insects, are 
carnivorous, bul their prey 
seems to include about as 
many beneficial insects as 
pests. The damage done by 
weevils, grasshoppers, and 
smooth caterpillars is noto- 
rious. Cutworms and army 
worms often do an immense 
amount of harm, and grass- 
hoppers frequently occur in 
such voracious hosts thai 
they sweep away every ves- 
tige of green vegetation be- 
fore them. On the other 
hand, carnivorous ground- 
beetles (Carabida 1 , see fig. 
<l) kill multitudes of insect 
pests, and certain parasitic wasp-like hymenopterous insects of the 
families Braconidse, Chalcididae, and Ichneumonidse destroy greal 
numbers of caterpillars. One of these parasitic insects will deposit 
in the back of a caterpillar from 20 to 2,000 eggs, which soon hatch 
into grub-like Larvae that feed upon the fatty tissues and exhaust 
the caterpillar so thai it is not able to transform 
into a perfect insect. 
The fact that birds do not discriminate between 
insects that aid the farmer, such as parasitic Hy- 
menoptcra and carnivorous ground-beetles, and 
those that are harmful to his interests, led the 
entomologist, Benjamin I). Walsh, to deny their 
asefulness as insect destroyers. He asserts that 
the good done by the consumption of insect pests 
is more than counterbalanced by the destruction 
of useful species. His argumenl is that there are 
thirty times as many individual insect pests as 
there are insect enemies which subsist upon them, 
and that therefore do insectivorous bird can be considered a 'public 
benefactor' until it can be shown to destroy at least thirty times as 
many injurious as beneficial insects. ' Applied to the destruction by 
birds of highly effective parasites of important pests which annually 
oral intervals cause a Large 1088 to Staple crops. Walsh's statement 
Kki.iI- Ground -lx-e tie 
• after Biley; loaned 
by Division <>f Ento- 
mology). 
«al Entomologist, Vol II. No. I. p. »;. 1807. 
