There is ample evidence that the Bembex is conscious of danger, and knows how disastrous for the future of her nest is the presence of the hated fly; her long efforts to throw the parasites off her track, her hesitation and flights, leave not a doubt on the subject. How is it then, I ask myself once more, that the enemy of Diptera should allow herself to be annoyed by another Dipteron—a tiny robber, incapable of the least resistance, which, if she chose, she could destroy instantly? Why, when once free from the prey which hampers her, does she not pounce on these ill-doers? What is needed to exterminate the evil brood around her burrow? Merely a battle which would take but a few instants. But the harmony of those laws which govern the preservation of species will not have it so, and the Bembex will always allow herself to be harassed without ever learning from the famous “struggle for life” the radical means of extermination. I have seen some which, pressed too closely, let fall their prey and flew off wildly, but without any hostile demonstration, although dropping their game left them full liberty of action. The prey, so ardently desired a moment earlier by the Tachinidæ, lay on the ground at the mercy of them all, and not one cared about it. It had no value for the flies, whose larvæ need the shelter of a burrow. It was valueless also to the Bembex, who came back, felt it for an instant and left it disdainfully. The little break in her custody of it had rendered her suspicious of it. Let us end this chapter by the history of the larva. Its monotonous life offers nothing remarkable during the two weeks while it eats and grows. Then comes making a cocoon. The slight development of silk-producing organs does not allow of a dwelling of pure silk, like those of the Ammophila and Sphegidæ—made of several wrappers which protect the larva, and later the nymph, from damp in the ill-protected, shallow burrow during autumn rains and winter snows. Yet this Bembex burrow is in worse conditions than those of the Sphex, being made at a depth of only a few inches in very permeable soil. To fashion a sufficient shelter the larva supplements by its industry the small amount of silk at its disposal. With grains of sand artistically put together and connected by silky matter, it constructs a most solid cocoon—impenetrable to damp.