Then ants have little "cows" of their own, which they "milk" regularly every day. These are the greenfly or aphis insects which do so much harm in our gardens and fields, plunging their beaks into the tender shoots and fresh green leaves of the plants, and sucking up their sap unceasingly. And as fast as they do so they pour the sap out again through two little tubes in their backs, in the form of a thin, sticky, very sweet liquid which we call honeydew. Now the ants are very fond of this liquid, and if you watch the greenfly insects which are almost always so plentiful on rose-bushes, you may see the ants come and tap them with their feelers. Then the little creatures will pour out a small quantity of honeydew from the tubes on their backs, which the ants will lick up. That is the way in which ants milk their little cows, and they are so fond of the honeydew that they will carry large numbers of these aphides into their nests and keep them, like a herd of cattle, all through the winter, so that they may never be without a supply of their favorite beverage! Ants, like bees and wasps, almost always consist of drones, queens, and workers. Only the drones and queens have wings, and these are seldom seen until the end of August. But then they make their appearance in vast swarms, which are sometimes so dense that from a little distance the insects really look like a column of smoke. They only take one short flight, however, and when this is over they come down to the ground and snap off their wings close to their bodies, just as termites do. One of the most curious of all these insects is the parasol-ant, of South America, which makes enormous dome-shaped nests of clay. But as the clay will not bind properly by itself, the insects work little pieces of green leaf up with it. These pieces of leaf are generally obtained from an orange plantation, perhaps half a mile distant. And when the ants are returning from their expedition, each holds its little piece of leaf over its head as it marches along, just as if it were carrying a tiny green parasol! Another very famous ant is the African driver, which owes its name to the way its vast armies drive every living creature before them. Insects, reptiles, antelopes, monkeys, even man himself, must give way before the advancing hosts of the drivers; for it is certain death to stand in their path. SAW-FLIES The saw-flies also belong to the order of the _Hymenoptera_. These flies are so called because the female insects have two little saws at the end of the body, which work in turns, one being pushed forward as the other is drawn back. With these they cut little grooves in the bark of twigs, or in the midribs of leaves, in which they place their eggs by means of the ovipositor between the saws.