The nesting habits of urnaria closely resemble those of the other members of the genus, as reported by various observers. The spot chosen is in firm soil, sometimes in open ground, but much more frequently under the leaves of some plant. The plan is a very simple one. A tunnel of about an inch in length leads to the pocket in which the caterpillars are stored. There is no hardening of the walls in any part. We took pains to draw every nest that we opened, and there was a very considerable variation in the minor details, such as the obliquity of the entrance tunnel, the shape of the pocket, and the angle at which the tunnel and pocket were joined. The work is done with the mandibles and the first legs. When it has proceeded so far that the wasp is partly hidden, she begins to carry the earth away from the nest. In doing this she backs up to the edge of the opening and, flying a little way, gives a sort of flirt which throws the pellet that she carries in her mandibles to a distance. She then alights where she is and pauses a moment before she runs back to the hole, or, in some cases, darts back on the wing. We watched the process of nest–making five times during the summer. In the first instance Ammophila, having made her excavation, ran off and after some search returned with a good–sized lump of earth. This she laid over the opening, which was now entirely hidden. She then flew to the bean patch close by, but after ten minutes she came back and looked at her nest. It was so neatly covered as to be almost indistinguishable, but to this fastidious little creature something seemed lacking. She pulled away the cover, carried out three or four more loads, and then began to search for another piece for closing. After a time she came hurrying back with a lump of earth, but when close to the nest she concluded that it would not do, dropped it, and ran off in another direction. Presently she found one which fitted into the hole exactly, and after placing it she brought a much smaller piece which she put above and to one side. She then stood back and surveyed the whole, and it seemed to us that we could read pride and satisfaction in her mien. She then flew away, and we supposed that that stage of the work was completed. Upon coming back two hours later, however, we found that she had been trying some more improvements, as a number of little pellets had been piled up over the nest. This wasp, by the way, never succeeded in finding a caterpillar, since when we opened the burrow a few days later it was still empty. Perhaps she came to some untimely end.