Wasps, Social and Solitary

by George W. Peckham; E. G. Peckham

NEST OF AMMOPHILA

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.

Of the other wasps that we saw making a temporary closure of their nests, one wedged a good-sized stone deep down into the neck of the burrow and then filled the space above, solidly, with smaller stones and earth. Another placed two lumps of earth just below the surface of the ground, filled the opening with pellets loosely thrown in, and then kicked some light dust over the whole. The others used only two or three lumps of earth, which they fitted neatly into the opening just below the surface. Although it is usual for urnaria to leave her nest closed while she is off searching for her prey, there is no invariable rule in the matter, even for single individuals. Once having seen a wasp dig her nest and close it up, we drew some radiating lines from the spot, in the light dust that covered the place, that we might find it again. When we returned, two hours later, the same wasp had made a nest four or five inches distant from the first one, and had left it wide open, while she had gone off to search for her caterpillar. She had probably been alarmed by the marks that we had made, and had felt it necessary to dig a new nest, but being in a hurry to lay her egg had omitted the usual process of closing it. We witnessed the storing of the caterpillar and the final closing.

From Fabre we learn that argentata and sabulosa close the nest as soon as it has been made, at least when the provisioning is to be postponed until the next day, while holosericea leaves it open until it is completely stored. He suggests an explanation for this variation by dwelling upon the inconvenience that would result if it were opened every time that the wasp brought in a caterpillar, since holosericea stores up five or six small larvæ instead of one or two large ones. But what, then, shall be said of polita and yarrowii, which, while they also store a number of small caterpillars, take pains to close and conceal the entrance every time they come out? We see the same habit in other genera where the mother continually passes in and out, as in Bembex and Oxybelus.

Fabre thinks that hirsuta has the habit, unusual for Ammophila, of catching her prey first and then digging the hole in which she bestows it. As she takes only one large caterpillar she is thus relieved of the necessity of closing the nest more than once.

As has been said, urnaria usually hunts a long time before she finds her caterpillar, and one or two days may pass before anything is put into the nest. During this prolonged search she often revisits the spot, and thus keeps fresh the memory of its locality. As soon as the first caterpillar is stored she lays an egg on it, and then closes the nest as before. The second one may be brought in within a few hours; but in one instance that came under our notice we feel sure that the interval was as much as three days. We saw the interment of the second caterpillar, and upon excavating, found on the first one a larva at least a day old; we suppose that at least two days had elapsed between the laying and the hatching of the egg.

When the provisioning is completed the time arrives for the final closing of the nest; and in this, as in all the processes of Ammophila, the character of the work differs with the individual. For example, of two wasps that we saw close their nests on the same day, one wedged two or three pellets into the top of the hole, kicked in a little dust, and then smoothed the surface over, finishing it all within five minutes. This one seemed possessed by a spirit of hurry and bustle, and did not believe in spending time on non-essentials. The other, on the contrary, was an artist, an idealist. She worked for an hour, first filling the neck of the burrow with fine earth which was jammed down with much energy,—this part of the work being accompanied by a loud and cheerful humming,—and next arranging the surface of the ground with scrupulous care, and sweeping every particle of dust to a distance. Even then she was not satisfied, but went scampering around, hunting for some fitting object to crown the whole. First she tried to drag a withered leaf to the spot, but the long stem stuck in the ground and embarrassed her. Relinquishing this, she ran along a branch of the plant under which she was working and, leaning over, picked up from the ground below a good-sized stone; but the effort was too much for her, and she turned a somersault on to the ground. She then started to bring a large lump of earth; but this evidently did not come up to her ideal, for she dropped it after a moment, and seizing another dry leaf carried it successfully to the spot and placed it directly over the nest. A third instance of the final closing of the nest was intermediate between these two, the work occupying twenty minutes. The wasp first put a plug well down, then dropped in several large pellets, brushed in a quantity of fine earth, and finally smoothed the surface over.

We had another much less worthy example, one, indeed, that went to the extreme of carelessness. We first saw her in the morning carrying her caterpillar across the field. She frequently dropped it and ran or flew to a little distance, and when she took it again the venter was sometimes up and sometimes down, whichever way it happened. Her nest was a very poor affair just beneath the surface, and after the caterpillar was carried in, it was visible from above. She filled the hole with loose particles of earth and then scratched the surface of the ground a little in a perfunctory sort of way, as different as possible from the painstaking labor that we had been accustomed to in her sisters. That afternoon we opened the nest and removed its contents. The next morning we saw this wasp bringing home her second caterpillar. She was much puzzled and disturbed at the destruction of her nest, and hunted for it for an hour and a half, leaving the caterpillar on the ground near by. We could not help feeling sorry that we had interrupted the contented routine of her life. She finally gave up in despair, and we took possession of the deserted caterpillar.

Just here must be told the story of one little wasp whose individuality stands out in our minds more distinctly than that of any of the others. We remember her as the most fastidious and perfect little worker of the whole season, so nice was she in her adaptation of means to ends, so busy and contented in her labor of love, and so pretty in her pride over the completed work. In filling up her nest she put her head down into it and bit away the loose earth from the sides, letting it fall to the bottom of the burrow, and then, after a quantity had accumulated, jammed it down with her head. Earth was then brought from the outside and pressed in, and then more was bitten from the sides. When, at last, the filling was level with the ground, she brought a quantity of fine grains of dirt to the spot, and picking up a small pebble in her mandibles, used it as a hammer in pounding them down with rapid strokes, thus making this spot as hard and firm as the surrounding surface. Before we could recover from our astonishment at this performance she had dropped her stone and was bringing more earth. We then threw ourselves down on the ground that not a motion might be lost, and in a moment we saw her pick up the pebble and again pound the earth into place with it, hammering now here and now there until all was level. Once more the whole process was repeated, and then the little creature, all unconscious of the commotion that she had aroused in our minds,—unconscious, indeed, of our very existence and intent only on doing her work and doing it well,—gave one final, comprehensive glance around and flew away.