In the course of the long and very able studies which they devoted to the biological investigations of the solitary wasps, George and Elizabeth Peckham1 have shown numerous individual variations in the habits of these insects. I will content myself with recalling one of the most striking. Ammophila urnaria examines its nest carefully before provisioning it, >and closes it each time that it carries a caterpillar to it. This closing is rapidly done, but after the last journey, when all of the victims have been put into place, the wasp closes its nest with much more care, each individual working according to his whim and the character of the place. This one contents itself with closing the orifice with a little sand which it rapidly collects, doing the wThole job in five minutes; another spends more than an hour in the work, carefully selecting its sand, which it mixes with fragments of leaves, covering the nest with a fine layer which it spreads out equally over the surface. These authors say:
1 G. W. and Elizabeth Peckham, Instincts and Habits of the Solitary Wasps, 1898. (Wisconsin Geol. & Nat. Hist. Surv. Bui. 2, sci. ser. 1).
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, 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 . . . and intent only on doing her work and doing it well, gavei one final comprehensive glance around, and flew away.
To smooth the earth which closes the nest is an instinctive habit of the species, but to employ in this operation a pebble which serves as a tool is no longer instinct ; it is a reasoning act, of which we find very few examples among animals. The Peokhams are exact and minute observers, confining themselves to facts, and quite opposed to anthropocentrism, which they ardently attack in their work. One can imagine the emotion which seized them when they found themselves in the presence of such a surprising case of individual variation. What adds to the interest of their observation is that it is not an isolated one. Several years before, Dr. S. W. Williston of Kansas had observed a variation of habit identical with this, with another species of Ammophila, namely Am-mophila yarrowi. Dr. Williston's observation was published in 1892 in "Entomological News," and the Peckhams rightfully believed it their duty to republish it in their book, the latter observation also relating to a single individual.