re for the very conspicuous
little insects on the broad bean, for example, whose dusky hue makes
them quite noticeable in large masses. Here there may very likely be
some special protection of nauseous taste in the aphides themselves (I
will confess that I have not ventured to try the experiment in person),
as in many other instances we know that conspicuously-coloured insects
advertise their nastiness, as it were, to the birds by their own
integuments, and so escape being eaten in mistake for any of their less
protected relatives.

On the other hand, it seems pretty clear that certain plants have
efficiently armed themselves against the aphides, in turn, by secreting
bitter or otherwise unpleasant juices. So far as I can discover, the
little plunderers seldom touch the pungent 'nasturtiums' or tropsaelums
of our flower-gardens, even when these grow side by side with other
plants on which the aphides are swarming. Often, indeed, I find winged
forms upon the leaf-stem of a nasturtium, having come there evidently in
hopes of starting a new colony; but usually in a dead or dying
condition--the pungent juice seems to have poisoned them. So, too,
spinach and lettuce may be covered with blight, while the bitter
spurges, the woolly-leaved arabis, and the strong-scented thyme close by
are utterly untouched. Plants seem to have acquired all these devices,
such as close networks of hair upon the leaves, strong essences, bitter
or pungent juices, and poisonous principles, mainly as deterrents for
insect enemies, of which caterpillars and plant-lice are by far the most
destructive. It would be unpardonable, of course, to write about
honey-dew without mentioning tobacco; and I may add parenthetically that
aphides are determined anti-tobacconists, nicotine, in fact, being a
deadly poison to them. Smoking with tobacco, or sprinkling with
tobacco-water, are familiar modes of getting rid of the unwelcome
intruders in gardens. Doubtless this peculiar property of the tobacco
plant has been developed as a prophylactic against insect enemies: and
if so, we may perhaps owe the weed itself, as a smokable leaf, to the
little aphides. Granting this hypothetical connection, the name of
honey-dew would indeed be a peculiarly appropriate one. I may mention in
passing that tobacco is quite fatal to almost all insects, a fact which
I present gratuitously to the blowers of counterblasts, who are at
liberty to make whatever use they choose of it. Quas