A Sphex appeared suddenly, whence I know not, dragging an ephippiger apparently just caught hard by. As things were she had to burrow, but the position was as bad as possible—a highway, hard as stone. There was no time for difficult mining, since the prey must be stored as soon as possible; she needed light soil where the cell could be quickly made. I have already described her favourite soil—dust deposed by years at the bottom of some hole in a wall, or in some little hollow of a rock. The Sphex which I was observing stopped at the foot of a country house with a newly whitewashed façade, and measuring from six to eight metres in height. Instinct told her that under the roof tiles she would find hollows rich in ancient dust. Leaving her prey at the foot of the façade, she flew on to the roof. For some time I saw her seek vainly about. Then, having found a suitable position, she set to work under the hollow of a tile. In ten minutes or a quarter of an hour at most the domicile was ready; she flew down, promptly found the ephippiger, and then had to carry up her prey. Would it be on the wing, as circumstances suggest? Not at all; the Sphex adopted the difficult method of escalading a vertical wall with a surface smoothed by the mason’s trowel and from six to eight metres high. Seeing her take this road, dragging her game between her feet, I thought at first that it was impossible, but was soon reassured as to the outcome of this audacious attempt. Supporting herself by the little roughnesses of the mortar, the vigorous insect, in spite of the embarrassment of her heavy load, made her way up this vertical plane with the same security, the same speed, as on horizontal ground. The top is reached without any hindrance, and the prey provisionally deposited at the edge of the roof on the rounded bark of a tile. While the Sphex was retouching her burrow the ill-balanced prey slipped and fell to the foot of the wall. She must begin again, and again by means of an escalade. The same imprudence is repeated; once more left on the curved tile the prey slips and falls to the ground. With a calm which such accidents cannot disturb, the Sphex for the third time hoists the ephippiger by climbing the wall, and, better advised, drags it straight to the bottom of the hole. If carrying the prey on the wing has not been attempted even in such conditions as the above, it is clear that the Sphex is incapable of flight with so heavy a load. To this impotence we owe the few details of habits which are the subject of this chapter. A prey not too heavy to be carried on the wing makes a semi-sociable species of S. flavipennis—that is to say, one seeking the company of its fellows; a heavy prey impossible to carry through the air renders S. occitanica a species devoted to solitary labour—a kind of savage, disdainful of the solace derived from neighbourhood of one’s fellows. The greater or lesser weight of their prey decides the fundamental character. XI