The nests of ants (Figs. 361, 362) are known under the name of ant-hills. They vary very much, both as to their form and the materials employed in making them--wood and earth are the principal. That which strikes one at first sight, is the size of these dwellings, which form a curious contrast to the smallness of their builders. Each species of ant has an order of architecture peculiar to it. The Red Ant (_Formica rufa_), one of the commonest in our woods, constructs a little rounded hillock with all kinds of objects--fragments of wood, bits of straw, dry leaves, the remains of insects, &c. This hillock, the base of which is protected by material of greater solidity, is nothing more than the exterior envelope of the nest, which is carried underground to a very great depth. Avenues, cleverly contrived, lead from the summit to the interior. The openings vary in width; and, as night approaches, are carefully barricaded. They are opened every morning, except on rainy days, when the doors remain shut, and the inhabitants confined within. The ant-hill, or _formicarium_, is at first simply a hole hollowed out in the soil, the entrance to which is masked by the building materials. But the miners do not cease to hollow out galleries and chambers, arranged by stories. The earth and rubbish are carried out, and serve to construct the upper edifice, which rises at the same time that the excavation grows deeper. It is a labyrinth bored in all directions. It contains corridors, landings, chambers, and spacious rooms, which communicate with each other by passages which are often vertical. All the corridors lead to a large central space, loftier than the others, and supported by pillars; it is here that the greater number of the ants congregate. These ant-hills often rise to a height of fifteen inches above the ground, and descend to an equal depth. Fig. 362 shows the interior of an ant-hill, drawn from Nature. Outside it are to be seen some ants occupied in sucking plant-lice. [Illustration: Fig. 362.--Section of an Ant-hill.] The group of Mason Ants contains a great number of varieties: the Ashy-black Ant (_Formica nigra_, Fig. 363), the Brown, the Yellow (_Formica flava_), the Blood-red, the Russety (_Polyergus rufescens_), the Black, the Miner (_Formica cunicularia_), the Turf Ant, &c. All these species employ a mortar, more or less fine, in raising their hillocks, at the same time that they hollow out their underground dwellings. The Jet Ant (_Formica fuliginosa_) excavates wood, hollowing out its labyrinth in the trunk of a tree with consummate skill. The Red Ant (_Myrmica rubra_) plies, according to circumstances, the trade of a mason or excavator. [Illustration: Fig. 363.--Ashy-black Ant (_Formica nigra_). Male, female, and worker.] [Illustration: Fig. 364.--Ashy Ant. Male, worker, and female.]