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At all events, the Bembex is not so infatuated with Fly as to refuse to abandon it for other game. The failure which I foresaw has proved a magnificent success. It is fairly convincing, is it not? Without the evidence of experiment, what can we rely upon?
These researches show us that in the Cerceris instinct is still subject to defect. In some neighbouring genera we can seize it, as it were, in process of formation. The way in which the Bembex, or Sand Wasp, provisions burrows by maternal foresight is much less mechanical than that of the Sphex. It is again Fabre who has described with most care the customs of this hymenopterous insect.
However this may be, the Bembex, returning to its burrow, is able to find it again with marvellous certainty, in spite of the care taken to hide it by removing every trace that might reveal its existence. It is guided by an extraordinary topographic instinct, which men not only do not possess, but cannot even understand the nature of. Souvenirs entomologiques, 1879, pp. 225 et seq.
Why a label which prepares the mind for an exceptional velocity and announces a race of peerless coursers? Nimble diggers of burrows and eager hunters the Tachytes are, to be sure, but they are no better than a host of rivals. Not the Sphex, nor the Ammophila, nor the Bembex, nor many another would admit herself beaten in either flying or running.
The Odynerus has for its instinctive mission to arrest the excessive multiplication of a lucerne weevil, no less than twenty-four of whose grubs are necessary to rear the offspring of the brigand, and nearly sixty gadflies are sacrificed to the growth of a single Bembex. Everywhere craft is organized to triumph over force.
Similarly those which have reason to fear for their offspring, if not for themselves, do nothing to evade the enemy which watches for them; the Megachile, although it could easily destroy it, is indifferent to the presence of a miserable midge, "the bandit who is always there, meditating its crime"; the Bembex, confronted with the Tachinarius, cannot control its terror, but nevertheless resigns itself, while squeaking with fright.
The same mode of work is employed by the Bembex-, Stizus-and Tachytes-wasps and other inlayers, who strengthen the inadequate woof of their cocoons with grains of sand; only, in their cotton-wool purses, the Anthidium's grubs substitute for the mineral particles the only solid materials at their disposal. For them, excrement takes the place of pebbles. And the work goes none the worse for it.
There, "lying flat on the ground, his head in the shadow of some rabbit's burrow," or sheltered from the sun by a great umbrella, "while the blue-winged locusts frisked for joy," he would follow the rapid and sibilant flight of the elegant Bembex, carrying their daily ration of diptera to her larvae, at the bottom of her burrow, deep in the fine sand."
Only the Bembex-wasps, which are plentiful in the sand of the neighbouring hills, might still afford me, without too prolonged a search, a few subjects on which to experiment. The Tarsal Bembex furnished me with what I wanted: larvae young enough to have still before them a long period of feeding and yet sufficiently developed to endure the trials of a removal.
Thus the Bembex, which especially attacks Diptera to make them the prey of its larvæ, throws itself suddenly on them and kills them with one blow in any part of the body. It is unable in this way to amass in advance sufficient provision for its larvæ; the corpses would putrefy. It is obliged to return from time to time bearing new pasture.
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