APHIS, (Encycl.) These insects are found in great numbers on the stems, leaves, and even roots of many trees and plants. Those trees that are most loaded with the insects, suffer greatly from them. The plant-lice thrust their sharp-pointed rostrum into the substance of the leaf to draw out their sustenance, which warps the stems and leaves, and occasions in the latter cavities underneath, and swellings above; nay, even in some, a kind of hollow gall filled with insects, as is often seen on elm-leaves.
It appears astonishing, that the slight puncture of so small an animal should so greatly disfigure a plant: but it must be remembered, that plant-lice always live in numerous associations, which increase visibly by the prodigious fruitfulness of those insects; so that altho' each puncture be slight, yet the number of them is so great, so reiterated, that it is no longer a wonder the leaves should be disfigured. And indeed lovers of gardening and plants seek to free and cleanse their trees from this vermin; but their care often proves unavailing, the insect is so fruitful that it soon produces a fresh colony. The best and surest method of extirpating it, is to put on the trees infested with them some larvae of the plant-louse-lion, or aphidivorous flies; for those voracious larvae destroy every day a great number of the insects, and that with so much the more facility, as the latter remain quiet and motionless in the neighbourhood of these dangerous enemies, who range over heaps of plant-lice, which they gradually waste and diminish.