INDIVIDUALLY the aphis is insignificant; collectively the aphides are a mighty army working incessant damage to man. Whether the locust, the caterpillar, or the aphis effects the greatest injury upon the vegetation necessary to man’s existence is a moot point. Were the locust to be found in all parts of the world, instead of being confined within comparatively limited regions, the palm would certainly be awarded to it, for the locust spares nothing, and destroys every green thing as its armies march along. The caterpillar and the aphis, although far more widely distributed, are less universal in their tastes, and fortunately neither of them has any partiality for cereals, the great staple of man’s food. It may well be believed, however, that were it not that the caterpillar is kept down by the ichneumon, and the aphis by the ladybird and other foes, both would in a very short time multiply so vastly that having devoured every other green thing they would be driven to fall upon the corn crops in their green stage; for when approaching ripeness the cereals are far too hard for mastication even by the jaws of the caterpillar, while the aphis might as well endeavour to obtain sustenance from a stone-wall. It is needless, however, here to enter into a detailed consideration as to the respective merits, or rather demerits, of the three insect scourges; it is enough that one aphis alone is fully capable, if left to its own devices, of developing in the course of a single year into a host so mighty that it would cover the land and wither up and devour all green things. While the caterpillar devours the substance of plants, the aphis only sucks their juices, and kills by so enfeebling the shoots that they are unable to put forth their leaves. It is an awkward, slow-moving creature, with its heavy green body swelled almost to bursting with vegetable juice, supported by legs so thin and fragile that they can scarce hold up its weight; and yet it seems to pervade all nature, and to appear at its season in vast armies, which fall almost simultaneously, it would seem, upon the plants it affects. So sudden and unaccountable is their appearance, that there are many persons who have maintained, and vast numbers still firmly believe, that the aphis is spontaneously produced from the juices of the plants it affects. The rose-grower will go into his garden and watch the young shoots from the leaves making vigorous progress, and he smiles to himself at the thought of how soon the sprays will be covered with rich blossoms. A cold night comes, followed perhaps by a day or two of dull weather. He shakes his head as he inspects his bushes, and marks how the delicate young leaves are slightly discoloured. He knows what will follow. Two or three days later every shoot is closely packed with a layer of the green fly sucking up its vital juices. It is not surprising that the grower absolutely refuses to believe that the whole of this infinite number of creatures were floating in the air waiting to pounce upon his plants at the very instant when, weakened by the frost, they are the less able to resist its attacks.

What renders the problem still more difficult is that the aphis army is not homogeneous. Each plant has its own tribe that prey upon its juices. The bean aphis differs from that of the rose, and this again from the hop fly; and, indeed, the number of varieties of aphis is exceedingly large. This greatly adds to the difficulty of explaining their simultaneous appearance in such countless numbers, for it would be necessary to imagine not only one army of aphides ready to sweep down upon vegetation weakened by frost or east wind, but a number of them, each selecting the particular plants they love, and rejecting all others—one hovering round the town looking out for the rose-trees in its suburbs, another scouring the rural districts in search of beans or peas, a third biding its time until drought or long spell of wet weather shall have weakened the hop bines to a point when they may be in a condition to suit its palate. It must be remembered that their appearance upon a certain plant is not gradual, but almost simultaneous. A week after a sharp frost on a May morning the whole of the rose growers in the district affected by the frost will find their plants attacked by the aphis, while the wail of the hop growers at the appearance of the fly will rise simultaneously over a whole district. The scientific explanation is that the appearance of the aphis in such vast numbers simultaneously is due to its prolific nature, but the practical man refuses to credit the suggestion. The aphis is prolific, but not prolific in the same way as is the white ant. The aphis will produce twenty-five offspring daily, but this will not account in any way for the fact that within a day or two of the pest making its appearance hundreds of thousands are to be found on every rose bush. Could the female aphis, like the termite, produce eighty thousand per day, the argument that the whole of the rose trees in a garden have been covered by the offspring of comparatively few females who found their way there might be accepted readily enough; but the rate of increase is incredible when we know that each female can produce but twenty-five young in twenty-four hours. It would need, then, not a few, but an infinite host of winged females, to account for the phenomenon. That many may pass the winter as eggs in the bark of trees and other places may be granted, but no one has yet observed the vast hordes streaming out from their places of concealment ready to start off in search of peas or beans, roses or hops. Moreover, in seasons favourable to vegetation, when neither frost nor east winds nor prolonged wet nor drought weaken the plants, and they grow robust and strong, what becomes of the armies of green fly that would, had the vegetation been sickly, have pounced down upon it? Nothing could be less scientific than these arguments, but as somehow there is common sense in them, they commend themselves to the minds of the foolish multitude, who, in spite of the teaching of their instructors, still believe the evidence of their own eyes that the aphis is the product of a certain unhealthy state of the juice of plants.

But although the increase at the rate of twenty-five per day by no means accounts for the almost simultaneous appearance of countless millions, it is a ratio that unless checked would by the end of the season absolutely cover the face of the earth, for the young ones so speedily become mothers that it is calculated the descendants of one aphis will during the season number 5,904,900,000. One objection on the part of scientific men to the spontaneous generation theory is that the aphis in other respects is an exception to the general law that governs the lives of all other creatures. It is not necessary for the aphis to have a father. The aphides that appear in spring are all females, and the process of multiplication and re-multiplication goes on with as much regularity as if the male sex had no part whatever in the economy of the world. It is only late in the autumn that the males appear, and it is not until after pairing that the females take to laying eggs, all the previous generations having been born alive. It is clear that when treating of a creature so unique in its habits and ways, the word “impossible” should never be used even by men so absolutely sure of what they assert as are scientific men. It is well, indeed, for man that the six thousand million possible descendants from each spring aphis do not put in their appearance. Happily nature, while in a moment of light-heartedness producing creatures possessed of such extraordinary powers of multiplication, and of no visible place or advantage in the general scheme of creation, thought proper to furnish them with a vast number of foes, whose life should be spent in ceaseless efforts to counteract the effects of this fertility. Chief among these stands the ladybird, but there are numerous others almost as indefatigable and voracious, even without counting man, with his tobacco juice, soap-suds, and fumigating apparatus. Nature has handed over the aphis defenceless to its destroyers. It possesses neither jaws nor sting; it is unprovided with armour, it cannot coil itself up like a wood louse, or assume a threatening aspect like the Devil’s Coach-horse. It is simply a helpless and unresisting victim, whose destiny is to do as much damage as it can to vegetation, and then to be slain. The closest observers have been unable to detect any signs of playfulness or of any other form of enjoyment in the aphis. Its existence is as monotonous as that of the vegetable the juices of which it drinks, and from the juices of which it is popularly believed to have sprung.