which may be central or wholly lateral. Usually a varnish is rubbed on the cells to prevent them being wetted by rain (Fig. 1).
The envelope of a typical cardboard-maker (Chartergus chartarius) is of a veritable cardboard, white, gray, yellow, or buff in color, smooth and solid, and impervious to the weather. It may be conical, cylindrical, almost globe-shaped, straight, but more often is a little curved. In the interior the platforms of cells differ from those of the common paper-making wasp in stretching right across like so many floors, being fastened on all sides to the walls. A simple hole perforates each, enabling the wasps to get from story to story. The form arises from the mode of enlargement of the dwelling. When the number of inhabitants becomes great and a fresh series of cells is required, these wasps do not, as a preliminary proceeding, amplify the envelope so as to extend the tiers; they first build cells, and cover them afterward. Beginning with the bottom of the nest, they set cells upon it, then lengthen the outer wall so as to include this fresh stage, and close in the end with a new floor, in its turn to become the ceiling of the next tier of cells when enlargement is again desired. No trace of the addition is suffered to remain and mar the covering, which would seem constructed at one stroke. Probably these wasps, like Myrapetra scutellaris (see Fig. 2), deviate from the ordinary habits of wasps in being collectors of honey.
It would be difficult to find a more peculiar nest than that of Myrapetra scutellaris. It is huge as compared with the insects, its brown cardboard wonderfully thick, hard, firm, and coarse in texture, and composed, not of wood fibers, but of the dung of the capincha, an aquatic cavy. The strange, fairly conical knobs that beset the surface of the envelope may defend the abode, which hangs low, against mammalia, such as tigers, jaguars, and cougars, that would plunder it of its honey; they appear to protect and conceal the entrance ways—of which, opposed to the custom of wasps, there are many—but they may be simple freaks of Nature. It seems odd for beings so sensible to put these projections on the end of the nest, no less than on the sides, necessitating their gnawing them away each time they add a stage; but probably they possess some means of softening the cardboard, and doubtless the same material, worked up afresh, helps to establish the new tier and the new cells.