Here is the only fact observed by myself that may throw a little light on the problem. Amid a colony of Sphex-wasps in full swing, a colony from which any other Wasp is usually excluded, I one day surprised a huntress of a different genus, Tachytes nigra, carrying one by one, without hurrying, in the midst of the crowd where she was but an intruder, grains of sand, bits of little dry stalks and other diminutive materials to stop up a burrow of the same shape and width as the adjacent burrows of the Sphex. The labour was too carefully performed to allow of any doubt of the presence of the worker’s egg in the tunnel. A Sphex moving about uneasily, apparently the lawful owner of the burrow, did not fail, each time that the strange Wasp entered the gallery, to rush in pursuit of her; but she emerged swiftly, as though frightened, followed by the other, who impassively continued her work. I inspected this burrow, evidently an object in dispute between the two Wasps, and found in it a cell provisioned with four Crickets. Suspicion almost makes way for certainty: these provisions are far in excess of the needs of a Tachytes-grub, who is certainly not more than half the size of the larva of the Sphex. She whose impassiveness, whose care to stop up the burrow would at first have made one take her for the mistress of the house, was in reality a mere usurper. How is it that the Sphex, who is larger and more powerful than her adversary, allows herself to be robbed with impunity, confining herself to fruitless pursuits and fleeing like a coward when the interloper, who does not even appear to notice her presence, turns round to leave the burrow? Can it be that, in insects as in man, the first chance of success lies in de l’audace, encore de l’audace et toujours de l’audace? The usurper certainly had audacity and to spare. I see her still, with imperturbable calmness, moving in and out in front of the complaisant Sphex, who stamps her feet with impatience but does not fall upon the thief.