Many species of caterpillars are not only skilful in concealing themselves in their cocoons, but also in the concealment of the cocoon itself; so that even when that is large, as in the instance of the death's-head hawk-moth (_Acherontia atropos_), it is almost impossible to find it. We allude to the numerous class of caterpillars which, previous to their changing into the pupa state, bury themselves in the earth. This circumstance would not be surprising, were it confined to those which are but too well known in gardens, from their feeding upon and destroying the roots of lettuce, chicory, and other plants, as they pass a considerable portion of their lives under ground; nor is it surprising that those which retire under ground during the day, and come abroad to feed in the night, should form their cocoons where they have been in the habit of concealing themselves. But it is very singular and unexpected, that caterpillars which pass the whole of their life on plants and even on trees, should afterwards bury themselves in the earth. Yet, the fact is, that perhaps a greater number make their cocoons under than above ground, particularly those which are not clothed with hair. Some of those caterpillars which go into the ground previous to their change make no cocoon at all, but are contented with a rude masonry of earth as a nest for their pupæ: into the details of their operations it will not be so necessary for us to go, as into those which exhibit more ingenuity and care. When one of the latter is dug up it has the appearance of nothing more than a small clod of earth, of a roundish or oblong shape, but, generally, by no means uniform. The interior, however, when it is laid open, always exhibits a cavity, smooth, polished, and regular, in which the cocoon or the chrysalis lies secure (Fig. B, p. 221). The polish of the interior is precisely such as might be given to soft earth by moistening and kneading it with great care. But beside this, it is usually lined with a tapestry of silk, more or less thick, though this cannot always be discovered without the aid of a magnifying glass. This species of caterpillars, as soon as they have completed their growth, go into the earth, scoop out, as the cossus does in wood, a hollow cell of an oblong form, and line it with pellets of earth, from the size of a grain of sand to that of a pea--united, by silk or gluten, into a fabric more or less compact, according to the species, but all of them fitted for protecting the inhabitant, during its winter sleep, against cold and moisture. [Illustration: Outside view of Nests of Earth-mason Caterpillars.] One of the examples of this occurs in the ghost-moth (_Hepialus humuli_), which, before it retires into the earth, feeds upon the roots of the hop or the burdock. Like other insects which construct cells under ground, it lines the cemented earthen walls of its cell with a smooth tapestry of silk, as closely woven as the web of the house-spider.