It is found, that where the saccharine substance has dropped from aphides for a length of time, as from the aphis salicis in particular, it gives to the silrface of the bark, foliage, Ike. that sooty kind of ap pearance, which arises from the explosion of gunpowder : it looks like, and is some times taken for, a Maid of black mildew. In most seasons the natural enemies attic aphides are sufficient to keep them in check, and to prevent them from doing essential injury to plants in the open air: hut there are times, once perhaps in four, five, or six years, in which they are mul tiplied to such an excess, that the usual means of diminution fail in preventing them from doing irreparable injury to certain crops.
To prevent the calamities which would infallibly result from an accumulates multiplication of the !Imre prolific animals. it has been ordained by the Author of nature, that such should be diminished by serving as food for others. On this principle, most animals of this kind have one or more natural enemies. The help less aphis, which is the scourge of the vegetable kingdom, has to contend with mane : of these, the principal are, the, coecinella, the ichneumon aphidum, and the muses aphidevom. The greatest de stroyer of the aphides is the coecinefia, or common ladybird. During the winter this insect secures itself under the bark of trees and elsewhere. When the spring expands the foliage of plants; the female deposits its eggs on them in great num bers, froin whence, in a short time, pro ceeds the larva, a small grub, of a dark lead-colour spotted with orange. These
may be observed in the summer season running pretty briskly over all kinds of plants, and, if narrowly watched, they will be found to devour the aphides wher ever they find them. The same may be observed of the lady-bird, in its perfect state. Another most formidable enemy to the aphis is a very minute, black, and slender ichneumon fly, -which eats its way out of the aphis, leaving the dry inflated skin of the insect adhering to the leaf like a small pearl : such may always be found where aphides are in plenty. Different species of aphides are.infested with dif ferent ichneumons. There is scarcely- a division of nature, in which the musezi or fly is not found : of these, one division, the aphidivora, feeds entirely on aphides. Of the different species of aphichvorous flies, which are numerous, having mostly bodies variegated with transverse stripes, their females may be seen hovering over plants infested with aphides, among which they deposit their eggs on.the surface of the leaf The larva, or maggot, produced from Such eggs, feeds, as selbn as hatched, on the younger kinds of aphis, and as it increases in size, attacks and devours those which are larger. The.larva of the hemerobius feeds also on the aphides, and deposits its eggs on the leaves of such plants as are beset with them. The earwig is likewise an enemy to them, especially such as reside in the curled leaves of fruit-trees, and the purses formed by cer tain aphides oti the poplars and other trees. To these may be added the small er soft-billed birds that feed on inseCts.