Some of these flies—more or fewer, generally three or four—have settled on the sand and are quite motionless, all gazing at the burrow, the entrance of which they know very well, carefully hid though it be. Their dull-brown colour, their large crimson-red eyes, their intense stillness, have often made me think of bandits who, dressed in a dark material, with a red kerchief over their heads, are lying in wait to do some evil deed. The Hymenopteron comes, loaded with prey. Had she no anxieties she would alight straightway at her door. Instead, she hovers at a certain height, descends slowly and circumspectly, hesitates, and vibrates her wings, producing a plaintive hum denoting apprehension. She must have seen the malefactors. They too have seen the Bembex. The movement of their red heads shows that they are following her with their eyes; every gaze is fixed on the coveted booty. Then come marches and counter-marches of cunning versus prudence. The Bembex drops straight down with an imperceptible flight, as if she let herself sink gently, making a parachute of her wings. Now she is hovering just above the ground; the flies take wing, placing themselves one and all behind her,—some nearer, some farther,—in a geometrical line. If she turns round to disconcert them, they turn too, with a precision which keeps them all in the same straight line; if she advances, so do they; if she draws back, they draw back too, measuring their flight, now slow, now stationary, on that of the Bembex at the head of the file. They do not attempt to fling themselves on the desired object, their tactics being merely to hold themselves in readiness in the position of rearguard, so as to avoid any hesitation when the rapid final manœuvre shall come. Sometimes, wearied out by their obstinate pursuit, the Bembex alights, and the flies instantly settle on the sand, still behind her, and keep quite still. She rises again, with a sharper hum—the sign no doubt of increasing indignation; the flies follow her. One last means remains to throw the tenacious Diptera off the track; the Bembex flies far away—perhaps hoping to mislead the parasites by rapid evolutions over the fields. But the crafty flies are not taken in; they let her go, and settle down again on the sand round the burrow. When the Bembex returns the same manœuvres begin again until the obstinacy of the parasites has exhausted her prudence. At a moment when her vigilance fails, the flies are instantly there. Whichever is at the most favourable point drops upon the vanishing prey, and the thing is done—the egg is laid.