land, or the puma and the wolverine in the settled
States of America, we should be so comparatively weak against the
Colorado beetle or the fourteen-year locust, and so absolutely powerless
against the hop-fly, the turnip-fly, and the phylloxera. The smaller and
the more insignificant our enemy, viewed individually, the more
difficult is he to cope with in the mass. All the elephants in the world
could have been hunted down and annihilated, in all probability, with
far less labour than has been expended upon one single little all but
microscopic parasite in France alone. The enormous rapidity of
reproduction in the family of aphides is the true cause of our
helplessness before them. It has been calculated that a single aphis may
during its own lifetime become the progenitor of 5,904,900,000
descendants. Each imperfect female produces about ninety young ones,
and lives long enough to see its children's children to the fifth
generation. Now, ninety multiplied by ninety four times over gives the
number above stated. Of course, this makes no allowance for casualties
which must be pretty frequent: but even so, the sum-total of aphides
produced within a small garden in a single summer must be something very
extraordinary.

It is curious, too, that aphides on the whole seem to escape the notice
of insect-eating birds very tolerably. I cannot, in fact, discover that
birds ever eat them, their chief real enemy being the little lizard-like
larva of the lady-bird, which devours them everywhere greedily in
immense numbers. Indeed, aphides form almost the sole food of the entire
lady-bird tribe in their earlier stages of existence; and there is no
better way of getting rid of blight on roses and other garden plants
than to bring in a good boxful of these active and voracious little
grubs from the fields and hedges. They will pounce upon the aphides
forthwith as a cat pounces upon the mice in a well-stocked barn or
farmyard. The two-spotted lady-bird in particular is the determined
exterminator of the destructive hop-fly, and is much beloved accordingly
by Kentish farmers. No doubt, one reason why birds do not readily see
the aphis of the rose and most other species is because of their
prevailing green tint, and the close way in which they stick to the
leaves or shoots on whose juices they are preying. But in the case of
many black and violet species, this protection of imitative colour is
wanting, and yet the birds do not seem to ca