These insects are not distinguished for any elaborate economy. Varying in the species, some prefer vertical banks, others sloping undulations, and again others horizontal flat ground or hard down-trodden pathways. Some burrow singly, and others are gregarious, collected in great numbers upon one spot. They are, perhaps, the most inartificial burrowers of all the bees. Their tunnels vary from five to nine or ten inches in depth, and in some species they are formed with other small tunnels slanting off from the main cylinder. The sides and bottom are merely smoothed, without either drapery or polish. The little cells thus formed are then supplied with the usual mixture of pollen and honey kneaded together, which in the larger species forms a mass of about the size of a moderate red currant, its instinct teaching it the quantity necessary for the nurture of the young which shall proceed from the egg that it then deposits upon this collected mass of food. The aperture of each little tunnel is closed with particles of the earth or sand wherein the insect burrows, and it proceeds to the elaboration of another receptacle for a fresh brood until its stock of eggs becomes exhausted. Some species have two broods hatched in the year, especially the earlier ones,—for several present themselves with the earliest flowers,—but others are restricted to but one. The quantity of pollen they collect is considerable, and in fact they are supplied with an apparatus additional to what is furnished to any of the other genera in a curled rather long lock of hair that emanates from the posterior trochanters. This, with the fringes that edge the lower portion and sides of the metathorax, as well as the usual apparatus upon the posterior legs, enables the insect to carry in each flight home a comparatively large quantity of pollen, but perhaps scarcely enough at once for the nurture of one young one, and it therefore repeats the same operation until sufficient is accumulated. The exact period occupied by their transformations is not strictly known; it will, of course, vary in the species, as also in those in which two broods succeed each other in the year, but the larva rapidly consumes its store and then undergoes its transformation. It does not spin a cocoon, but in its pupa state it is covered all over with a thin pellicle, which adheres closely to all the distinct parts of the body. It is not known how this is formed; perhaps it is a membrane which transudes in a secretion through the skin of the larva, or it may be this itself converted to its new use, which seems to be for the protection of all the parts of the now transmuting imago, until these in due course shall have acquired their proper consistency.