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In conformity with the Darwinian ideas, we have accepted an unknown precursor, who by dint of repeated experiment, adopted as the victuals to be hoarded the larvae of the Scarabaeidae.
They are all open but still fresh: they date from the present generation; the Scoliae whom I unearth have quitted them not long since. I learnt later, in fact, that the hatching took place in the course of July. In the same heap of mould is a swarming colony of Scarabaeidae in the form of larvae, nymphs and adult insects.
My lack of success was due to the uncertainty of my excavations, in which I had nothing to guide me over the indefinite area covered. If I could at least identify the Scarabaeidae whose larvae form the prey of the two Scoliae, the problem would be half solved. Let us try. I collect all that the luchet has turned up: larvae, nymphs and adult Beetles.
Environment, diet, industry and internal structure are all similar; and yet one of these three larvae, the Cetonia's, reveals a most singular dissimilarity from its fellow-trenchermen: alone among the Scarabaeidae and, more than that, alone in all the immense order of insects, it walks upon its back.
I examined this shred of skin with all the care that it deserved. My first suspicions were confirmed: a Lamellicorn, a Scarabaeid in the larval state, is the first food of the Wasp whose cocoon I have just unearthed. But which of the Scarabaeidae? And does this cocoon, my precious booty, really belong to the Scoliae? The problem is beginning to take shape.
Perhaps she even assails other larvae, inhabitants, like the foregoing, of heaps of rotting vegetable-matter. I therefore set down the Cetonia genus generally as forming the prey of the Two-banded Scolia. Oryctes, Cetoniae and Anoxiae in the larval state: here then is the prey of the three Scoliae whose habits we know. The three Beetles are Lamellicorns, Scarabaeidae.
The Garden Scolia attacks Oryctes nasicornis; the Two-banded Scolia the Cetonia; the Interrupted Scolia the Anoxia. All three operate below ground, under the most unfavourable conditions; and all three have for their victim a larva of one of the Scarabaeidae, which, thanks to the exceptional arrangement of its nerve-centres, lends itself, alone of all larvae, to the Wasp's successful enterprises.
Physiology perceived what anatomy had not yet revealed, at all events to my eyes, for since then, on dipping into my books, I have learnt that these anatomical peculiarities, which were then so new to me, are now within the domain of current science. We know that, in the Scarabaeidae, both the larva and the perfect insect are endowed with a concentrated nervous system.
The Scoliae, then, whose destiny it is to hunt and paralyse under the soil the victuals for their family, require a prey made highly vulnerable by the close assemblage of the nerve-centres, as are the Weevils and Buprestes of the Cerceres; and this is why it has fallen to their lot to share among them the larvae of the Scarabaeidae.
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