Let us observe the tactics employed by the Tachinid, whose object is to confide her egg to the nest of the miner. It is an invariable rule that the fly should never penetrate into the burrow, even if left open and the owner absent. The crafty parasite would take good care not to entangle itself in a passage, where, having no possibility of flight, it might pay dearly for its effrontery. The only moment for its designs—a moment watched for with the greatest patience—is that when the Hymenopteron enters the gallery, clasping her prey. At that instant, brief as it is, when the Bembex or any other miner has half her body within the entrance, and is about to disappear underground, the Miltogramma arrives on the wing, perches on the prey slightly, projecting beyond the hinder end of the Bembex, and while she is delayed by the difficulties of entering, the Miltogramma, with unparalleled promptitude, lays an egg on the prey, or two, or even three eggs, successively. The hesitation of the Bembex, embarrassed by her load, lasts but the twinkling of an eye; but that matters not—it is long enough for the fly to accomplish its misdeed without being dragged beyond the threshold. What must not be the suppleness of organs to achieve this instantaneous laying of the egg! The Bembex disappears, herself introducing the enemy, and the Tachinid goes and crouches in the sun, close to the burrow, and meditates fresh crimes. If one would make sure that the Dipteron’s eggs have really been deposited during this rapid manœuvre, it suffices to open the burrow and follow the Bembex to the bottom of her abode. The prey which one takes from her bears underneath at least one egg—sometimes more, according to the length of the delay at the entrance. These very minute eggs could only belong to a parasite, and if any doubt remained, you can bring up the brood in a box, and the result will be Diptera larvæ—later pupæ, and finally Miltogramma. The fly shows wonderful sagacity in the moment selected by it—the only one which could permit of her carrying out her purpose with neither peril nor vain efforts. The Bembex, half-way through the entrance, cannot see her enemy audaciously perched on the hind quarters of the prey, or, if she suspects the bandit’s presence, cannot drive it away, having no freedom of movement in the strait passage, and in spite of all precautions to facilitate speedy entrance, cannot always vanish underground with the celerity required, so quick is the parasite. In fact, this is the only propitious moment, since prudence forbids the Dipteron to penetrate into the den, where other Diptera, far stronger than itself, are served up as food for the larvæ. Outside, in the open air, the difficulty is insurmountable, so great is the vigilance of the Bembex. Let us give a moment to the arrival of the mother, when the nest is being watched by the Miltogramma.