The nests are almost always chambered cavities, hollowed out either in the ground, in walls, and similar situations, or in dead and decaying wood. One of the commonest examples in our own country is the Garden Ant (_Formica nigra_), which may be found everywhere in gardens making its nest in the ground. Another common species is the pretty Turf Ant (_Formica flava_), which generally haunts commons and heaths, casting up small hills, which serve to throw off the rain; and this species in some localities makes its nest under stones. The Wood Ant (_Formica lignipeda_) is another familiar species. [Illustration: Fig. 27.--Formica Lignipeda (Worker). (Mag.)] A very large group of ants belong to the section _Myrmicinæ_, the best-known species of which are the Red Ants, _Myrmica rubra_, and their allies. [Illustration: Fig. 28.--Myrmica Rubra (Male). (Mag.)] A very minute species which has been introduced into this country, probably from Brazil or the West Indies, is the Horse Ant (_Myrmica molesta_). It is a very small brownish-yellow species, which seems to have been first observed in England in 1828. It takes up its abode in houses, frequently in the neighbourhood of the kitchen fireplace, and when it multiplies becomes such a pest as to render the house uninhabitable. Some of the metropolitan districts have been particularly infested. TRIBE II.--ENTOMOPHAGA. Most of the insects belonging to this tribe are parasitic on other insects. The _larvæ_ are footless. There are seven families included in the _Entomophaga_. [Illustration: Fig. 29.--Cynips Gallæ Tinctoriæ (Mag.)] _Family 18, Cynipidæ._--This family includes most of the gall flies. The number of species is very considerable. Of the great majority the females pierce with their ovipositor the tissues of plants and trees, and there deposit their eggs, from which the _larvæ_ are soon hatched. The irritation caused by this intrusion of a foreign body into the tissues produces the galls which are so commonly met with. [Illustration: Fig. 30.--Smicra Sispes (Mag.)] The galls produced by different species of flies differ greatly in form and structure. Some of them are round and smooth, like fruits, such as the cherry gall of the oak leaves, produced by the puncture of _Cynips quercus-foli_. The most singular, however, of all the galls is perhaps the Bedeguar, which is formed on the stems of wild roses by the puncture of a small species, _Rhodites rosæ_. _Family 19, Chalcididæ._--To this family belong many gall insects, principally found, however, in foreign countries. The _Chalcididæ_ include a great number of small species, few exceeding half an inch in expanse. Many of these are singular in shape, and others brilliantly metallic; but, owing to their small size, they have hitherto been studied by comparatively few entomologists. [Illustration: Fig. 31.--Thoracamba Furcata (Mag.)]