Essays on the Microscope: Containing a Practical Description of the Most Improved Microscopes, a General History of Insects, etc., etc.Adams, George
Science
Essays on the Microscope: Containing a Practical Description of the Most Improved Microscopes, a General History of Insects, etc., etc.
Adams, George
Insects -- Early works to 1800; Microscopy -- Early works to 1800
some tender shoots, and left to provide for itself.
In the spring months there appear on the rose-trees but two generations
of aphides, including those which proceed immediately from the last
year’s eggs; the warmth of the summer adds so much to their fertility,
that no less than five generations succeed one another in the interval.
One is produced in May, which casts off its covering; while the months
of June and July each supply two more, which cast off their coverings
three or four times, according to the different warmth of the season.
This frequent change of their outward coat is the more extraordinary,
because it is repeated more often when the insects come the soonest to
their growth, which sometimes happens in ten days, where warmth and
plenty of nourishment conspired.
Early in the month of June, some of the third generation, which were
produced about the middle of May, after casting off their last covering,
discover four erect wings, much longer than their bodies; and the same
is observable in all the succeeding generations which are produced
during the summer months, but still without any diversity of sex; for
some time before the aphides come to their full growth, it is easy to
distinguish which will have wings, by a remarkable fullness of the
breast, which in the others is hardly to be distinguished from the body.
When the last covering is rejected, the wings, which were before folded
up in a very narrow compass, are gradually extended in a surprizing
manner, till their dimensions are at last very considerable.
The increase of these insects in the summer time is so very great, that
by wounding and exhausting the tender shoots, they would frequently
suppress all vegetation, had they not many enemies to restrain them.
Notwithstanding these insects have a numerous tribe of enemies, they are
not without friends, if those may be considered as such, who are
officious in their attendance for the good things they expect to reap
thereby. The ant and the bee are of this kind, collecting the honey in
which the aphides abound, but with this difference, that the ants are
constant visitors, the bee only when flowers are scarce; the ants will
suck in the honey while the aphides are in the act of discharging it,
the bees only collect it from the leaves on which it has fallen.
In the autumn three more generations of aphides are produced, two of
which generally make their appearance in the month of August, and the
third before the middle of September. The two first differ in no respect
from those which are found in summer; but the third differs greatly from
all the rest. Though all the aphides which have hitherto appeared were
females, in this tenth generation several male insects are found, but
not by any means so numerous as the females.
Public-domain text, read in full here on John Shaqi.
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