Yet she must have known that the burrow was empty, since she had gone inside, and made prolonged stay, but yet after this visit to the plundered dwelling, she set to work to close it with as much care as if nothing had happened. Did she propose to turn it later to account, returning with a fresh prey, and laying a new egg? In that case the burrow was closed to defend it from indiscreet visitors while the Sphex was away. Or it was a measure of prudence against other miners who might covet a ready-made chamber, or a wise precaution against internal wear and tear, and, in fact, some predatory Hymenoptera are careful when obliged to suspend work to defend the mouth of their burrow by closing it up temporarily. I have seen certain Ammophilæ, whose burrow is a vertical well, close the entrance with a little flat stone when the insect goes a-hunting, or stops mining when the hour to leave off work comes at sunset. But in that case the stoppage is slight—a mere slab set on the top of the well. It takes but a moment when the insect comes to displace the little flat stone, and the door is open. But what we have just seen the Sphex construct is a solid barrier—strong masonry, where layers of alternate dust and gravel occupy the whole passage. It is definitive, and no temporary work, as is sufficiently shown by the careful way in which it is constructed. Besides, as I think I have already proved, it is very doubtful, considering the manner in which she acted, whether the Sphex would return to use the dwelling which she had prepared. A new ephippiger will be caught elsewhere, and elsewhere too will the storehouse destined for it be hollowed. As, however, these are but conclusions drawn by reasoning, let us consult experiment, more conclusive here than logic. I let nearly a week pass in order to allow the Sphex to return to the burrow so methodically closed, and use it if she liked for her nest-laying. Events answered to the logical deduction; the burrow was just as I had left it, well closed, but without food, egg, or larva. The demonstration was decisive; the Sphex had not returned.