Here is the home uncovered, in the bright light, under the sun’s rays. How will the mother behave on her return? Let us consider the question in detail, according to scientific precepts: it is a perplexing position for the observer, as my recent experiences make me suspect. Here is the problem: the mother on arriving has the feeding of her larva as her object in view; but to reach this larva she must first find the door. The grub and the entrance-door: those are the two aspects of the question that appear to me to merit separate consideration. I therefore take away the grub, together with the provisions, and the end of the passage becomes a clear space. After making these preparations there is nothing to do but exercise patience. The Wasp arrives at last and goes straight to where its door ought to be, that door of which naught but the threshold remains. Here, for more than an hour, I see her digging on the surface, sweeping, making the sand fly, and persisting, not in scooping out a new gallery, but in looking for that loose door which ought easily to give way before a mere push of the head and let the insect through. Instead of yielding materials, she finds firm soil, not yet disturbed. Warned by this resistance, she confines herself to exploring the surface, always in close proximity to the spot where the entrance should be. A few inches on either side is all that she allows herself. The places which she has already tested and swept twenty times over she returns to test and sweep again, unable to bring herself to leave her narrow radius, so obstinate is her conviction that the door must be here and not elsewhere. Several times in succession I push her gently with a straw to some other point. She will not be put off: she returns straightway to the place where her door once stood. At rare intervals the gallery, now an open trench, seems to attract her attention, though very faintly. The Bembex takes a few steps towards it, still raking, and then goes back to the entrance. Twice or thrice I see her run the whole length of the conduit and reach the blind alley, the abode of her grub; here she gives a few careless strokes of the rake and hurries back to the spot where the entrance used to be, continuing her quest there with a persistency that ends by wearying mine. More than an hour has passed and the stubborn Wasp is still pursuing her search on the site of the vanished doorway. What will happen when the larva is present? This is the next aspect of the question. To continue the experiment with the same Bembex would not have given me the positive evidence which I wanted, for the insect, rendered more obstinate by its vain quest, seemed to me now obsessed by a fixed idea, which would certainly have obscured the facts which I wished to ascertain. I needed a fresh subject, one not over-excited and solely concerned with the impulses of the first moment. An opportunity soon presented itself.