The carder-bees select for their nest a shallow excavation about half a foot in diameter; but when they cannot find one to suit their purpose, they undertake the Herculean task of digging one themselves. They cover this hollow with a dome of moss--sometimes, as we have ascertained, of withered grass. They make use, indeed, of whatever materials may be within their reach; for they do not attempt to bring anything from a distance, not even when they are deprived of the greater portion by an experimental naturalist. Their only method of transporting materials to the building is by pushing them along the ground--the bee, for that purpose, working backwards, with its head turned from the nest. If there is only one bee engaged in this labour, as usually happens in the early spring, when a nest is founded by a solitary female who has outlived the winter, she transports her little bundles of moss or grass by successive backward pushes, till she gets them home. In the latter part of the season, when the hive is populous and can afford more hands, there is an ingenious division of this labour. A file of bees, to the number sometimes of half a dozen, is established, from the nest to the moss or grass which they intend to use, the heads of all the file of bees being turned from the nest and towards the material. The last bee of the file lays hold of some of the moss with her mandibles, disentangles it from the rest, and having _carded_ it with her fore legs into a sort of felt or small bundle, she pushes it under her body to the next bee, who passes it in the same manner to the next, and so on till it is brought to the border of the nest,--in the same way as we sometimes see sugar-loaves conveyed from a cart to a warehouse, by a file of porters throwing them from one to another. The elevation of the dome, which is all built from the interior, is from four to six inches above the level of the field. Beside the moss or grass, they frequently employ coarse wax to form the ceiling of the vault, for the purpose of keeping out rain, and preventing high winds from destroying it. Before this finishing is given to the nest, we have remarked, that on a fine sunshiny day the upper portion of the dome was opened to the extent of more than an inch, in order, we suppose, to forward the hatching of the eggs in the interior; but on the approach of night this was carefully covered in again. It was remarkable that the opening which we have just mentioned was never used by the bees for either their entrance or their exit from the nest, though they were all at work there, and, of course, would have found it the readiest and easiest passage; but they invariably made their exit and their entrance through the covert-way or gallery which opens at the bottom of the nest, and, in some nests, is about a foot long and half an inch wide. This is, no doubt, intended for concealment from field-mice, polecats, wasps, and other depredators.