Aphides (ăf′ĭ-dēz), small insects very injurious to plants and commonly called plant-lice. The number of species is very large, and they live on a great variety of plants. They are usually greenish in color, with short bodies and long slender legs. Their mouth parts are formed into a short stylet, through which they suck the juices of plants. They prey practically upon all cultivated plants, and increase so rapidly that were it not for their numerous enemies plant life would almost be destroyed. The grapevine phylloxera is very destructive to vineyards; a great pest is the root-louse of the apple, mistakenly called the American blight; another great pest the hop plant louse; and others, the aphides of the cabbage, potato, bean, apple, pear, etc., have carried wide destruction. They are produced in large numbers, and have natural enemies, like the larvae of the lady-bird. Tobacco and a strong solution of soap and kerosene emulsion are used in combating them.
Many forms of aphide produce a sweet liquid, called honey-dew, of which ants are very fond. Ants are known to keep herds of them as "milch cows" in captivity, protecting them from their enemies and stroking them with their antennae in order to make them give up the honey-dew.