feeler; a
pair of mandibles (_b_), often covered with several rows of fine teeth,
and ending in three or four larger hooks and a serrated labium (_a_).
These parts form a beak which the mite or tick insinuates into the flesh
of its host, upon the blood of which it subsists. While many of the
mites are parasitic on animals, some are known to devour the eggs of
insects and other mites, thrusting their beaks into the egg, and sucking
the contents. We have seen a mite (Nothrus ovivorus, Fig. 143) busily
engaged in destroying the eggs of a moth like that of the Canker worm,
and Dr. Shimer has observed the Acarus? malus sucking the eggs of the
Chinch bug. I have also observed another mite devouring the Aphides on
the rose leaves in my garden, so that a few mites may be set down as
beneficial to vegetation. While a few species are injurious to man, the
larger part are beneficial, being either parasitic and baneful to other
noxious animals, or more directly useful as scavengers, removing
decaying animal and vegetable substances.

[Illustration: 142, Ixodes albipictus and young.[8]]

The transformations of the mites are interesting to the philosophic
zoologist, since the young of certain forms are remarkably different
from the adults, and in reaching the perfect state the mite passes
through a metamorphosis more striking than that of many insects. The
young on leaving the egg have six legs, as we have seen in the case of
the Ixodes. Sometimes, however, as, for example, in the larva, as we may
call it, of a European mite, Typhlodromus pyri, the adult of which,
according to A. Scheuten, is allied to Acarus, and lives under the
epidermis of the leaves of the pear in Europe (while Mr. T. Taylor, of
the Department of Agriculture at Washington, has found a species in the
pear leaves about Washington, and still another form in peach leaves),
there are but two pairs of legs present, and the body is long,
cylindrical and in a degree worm-like.

I have had the good fortune to observe the different stages of a bird
mite, intermediate in its form between the Acarus and Sarcoptes, or Itch
mite. On March 6th, Mr. C. Cooke called my attention to certain little
mites which were situated on the narrow groove between the main stem of
the barb and the outer edge of the barbules of the feathers of the Downy
Woodpecker, and subsequently we found the other forms in the down under
the feathers. These long worm-like mites were evidently the young of