The mirror. (Stillwater, Minn.) 1894-1925, 1918-01-17

with small rodents, to save the
western farmers upwards of a hun
dred thousand dollars year.
If all insects preyed upon vege-
tation, our inquiry into the value
of insect eating birds need 60 nc
further, since all of them might be
set down as beneficial. But by nc
means all insects are destructive OF
vegetation. and their relations tt
each other and to birds are very
complex and puzzling.
| The insects that feed on vegeta-
tion at some stage or other of their
extence probably outnumber all
others, both in number of species
and of individuals; but there are
two other classes of insects which
deserve attention here, the pre-
daceous and the parasitic. The
predaceous insects, either in the
adult or larval state, feed upon
other insects and hence in the main
are beneficial.
| It would seem, therefore, that
in so far as birds destroy preda-
ceous insects they do harm. That
birds do destroy a greater or less
number cannot be denied, but as
many species of this group secrete
nauseous fluids, which serve to, in
a measure at least, to protect them,
and as many are of retiring habits
and are not readily found. the num-
Der destroyed by birds is relatively
not large.
| Moreover, some of the preda-
ceous insects, when insect food is
not available, become vegetarians,
and hence assume the role of ene-
mics of the farmer; so that when
birds destroy predaceous insects
they may be doing the farmer
either a good turn or an i'll turn,
according to circumstances. The
, relation of birds to the so-called
parasitic insects is still more intri-
cate and puzzling.
| Parasitic insects fill very i'm
portant place in the economy of
nature. 1t is even claimed by en-
tomologists that they do more ef-
fective service in aiding to keep a
true balance in the insect world
than any other agency. They at
tack insects in every stage of exist.
ence and insure their destruction
by depositing eggs on, or in, the
bodies of adults, their larvae, or
their eggs. Now, birds recognize
no fine distinction in the insect
world; all is grist that comes to
the avian mill, and parasitic insects
are snapped up by birds without
the slightest regard to the fact that
} they are useful to man. Hence,
we have a complicated problem to
! unravel in respect to the inter-re-
lation of insect pests, of insect
parasites that destroy them, and OF
the birds that destroy both pests
and their parasites.
After due recognition of the
part insect parasites play in the
economy of nature, it is evident
that, unassisted, they are unequal
} to the task of keeping insect life in
. a proper state of balance. In this
work birds play an important,
though it may be relatively some
i. what subordinate part. Had para
site and predaceous insects been
J equal to the task of holding in
!. check insect pests, there would be
: no place in the world for insect
eating birds. In the progress OF
evolution, however, long after in
sects and insect parasites appeared,
birds found a place vacant, which
even their reptilian ancestors had
not been able to occupy, and pro.
ceeded to fill it. Having once
gained a place in the world, birds
entered into competitive struggle
Z with each other and with other in.
sect-eaters. In course of time they
/ developed into a great number O1
families, each distinguished by pc.
culiarities of form, plumage anc
) habits, and each endowed with
i