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.
Some of these insects are extremely mischievous. The grub of the turnip saw-fly, for instance, often destroys whole fields of turnips, while the currant saw-fly is equally destructive to currants and gooseberries. One often sees bushes which it has entirely stripped of their leaves.
You may always know a saw-fly grub by the fact that it has no less than twenty-two legs—three pairs of true legs on the front part of the body, and eight pairs of false legs, or prolegs, as they are often called, on the hinder part.
There is one little family of saw-flies, however, which are quite unlike all the rest, for instead of having saws at the ends of their bodies, they have long boring instruments, very much like brad-awls. With these they bore deep holes in the trunks of fir-trees, in order to place their eggs at the bottom; and the grubs feed, when they hatch out, on the solid wood.
These insects are known as horn-tailed saw-flies, and one, which is very common in pine woods, is very large, sometimes measuring an inch and a half from the head to the tip of the tail, and very nearly three inches across the wings, while the boring tool is fully an inch long. It is a very handsome insect, and looks rather like a hornet, the head and thorax being deep glossy black and the hind body bright yellow, with a broad black belt round the middle. The feelers are also yellow, and the legs are partly yellow and partly black.
Gall-Flies
Another group of the Hymenoptera consists of the gall-flies. These are all small insects, which lay their eggs in little holes which they bore in roots, twigs, and the ribs and nervures of leaves. In each hole, together with the egg, they place a tiny drop of an irritating liquid, which causes a swelling to take place, on the substance of which the little grub feeds. Sometimes these galls, as they are called, take most curious forms. The pretty red and white oak-apples of course you know; and no doubt, too, you have often found the hard, woody, marble-shaped galls which are so common on the twigs of the same tree. Then some galls look like bunches of currants, and some look like scales, and some look like pieces of sponge. And if you cut one of them open you will find perhaps one little grub, or perhaps several, curled up inside them.