The moment adopted by the Gnat is chosen with great discrimination: it is the only moment when she is able to accomplish her designs without danger, and without useless dodging about. The Wasp, half-trapped in the entrance-hall, cannot see the foe so daringly perched on the hind-quarters of the prey; if she suspects the parasite’s presence, she cannot drive her away, having no liberty of movement in the narrow corridor; lastly, in spite of all the precautions which she takes to facilitate her entrance, she cannot always vanish underground with the necessary speed, the fact being that the bandit is much too quick for her. This indeed is the auspicious moment and the only one, since prudence forbids the Fly to penetrate into the cave where other Flies, far stronger than herself, serve as food for the grub. Outside, in the open air, the difficulty is insurmountable, thanks to the intense vigilance of the Bembex. Let us turn for a minute to the arrival of the mother while her home is being watched by Miltogrammæ. A number of these Midges, greater or less from time to time but usually three or four, station themselves on the sand and remain perfectly still, all gazing at the burrow, of which they well know the entrance, carefully hidden though it be. Their dull-brown colour, their great blood-red eyes, their indefatigable patience have often suggested to me a picture of brigands, clad in dark frieze, with a red handkerchief round their heads, waiting in ambush for the moment to strike a felon blow. The Wasp arrives carrying her prey. If nothing of an alarming nature troubled her, she would then and there alight at her door. But she hovers at a certain height, comes down slowly and circumspectly, hesitates; and a plaintive whimpering, resulting from a special vibration of her wings, expresses her fears. She has seen the malefactors therefore. They too have seen the Bembex: they follow her with their eyes, as the movement of their red heads shows; every gaze is turned towards the coveted booty. Now come the marches and countermarches of craft striving to outwit prudence.