The Mason-Wasps

by Jean-Henri Fabre

Why do I linger over a petty detail which the famous historian of the Odyneri tells in half-a-dozen words? A petty detail? It is nothing of the kind; on the contrary, it is a circumstance of paramount importance. And this is why: the egg is laid at the back, necessitating an empty cell which will be victualled after the egg is laid. The provisions are now stored, piece by piece, layer upon layer, in front of the egg; the cell is crammed with game right up to the entrance, which in the end is sealed.

Of all these pieces, the obtaining of which may take several days, which are the earliest in point of date? Those nearest the egg. Which are the latest? Those by the entrance. Now it is obvious—besides, it may be proved, if necessary, by direct observation—it is obvious, I say, that the heaped worms lose strength from day to day. The effects of a prolonged fast would be enough to produce this result, to say nothing of the disorders due to a wound which becomes worse as time goes on. The larva born at the back of the cell has therefore beside it, in its first youth, the less dangerous provisions, the oldest in date and consequently the feeblest. As it works its way through the heap, it finds more recent [[53]]game, which is also more vigorous; but this is attacked without danger, because the larva’s own strength has come.

This progress from the more to the less nearly mortified victims presumes that the grubs do not disturb the order in which they have been stacked. That in fact is what happens. Former historians of the Odyneri have all remarked that the grubs provided for the larva are curled in the shape of a ring:

“The cell,” says Réaumur, “was occupied by green rings, to the number of eight or twelve. Each of these rings consisted of a vermiform larva, alive, curled up and with its back fitting exactly against the wall of the hole. These grubs, laid in this way one on top of the other and even pressed together, had no liberty of movement.”

I, in my turn, remark similar facts in my two dozen grub-worms. They are curled in a ring; they are stacked one upon another, but with a certain confusion in the ranks; their backs touch the wall. I will not attribute this circular curve to the effect of the sting which was very probably administered, for I have never observed it in [[54]]the caterpillars stabbed by the Ammophilæ; I believe rather that the position is natural to the grub during inaction, even as it is natural for the Iuli[12] to coil themselves into a spiral. In this living bracelet there is a tendency to return to the rectilinear conformation; it is a bent bow fighting against the obstacle that surrounds it. By the very fact, therefore, of being curled up, each grub keeps more or less steady by pressing its back a little against the wall; and it retains its place even when the cell approaches the vertical.

Moreover, the shape of the cell has been calculated with a view to this manner of storing. In the part next the entrance, the part which one might call the store-room, the cell is cylindrical and narrow, so as to afford the living rings as little space as possible; they are thus kept in position and are unable to slip. It is here that the grubs are stacked, squeezed one against the other. At the other end, near the back, the cell expands into an ovoid to give the larva elbow-room. The differences between the two diameters is very perceptible. At the entrance I find only four millimetres:[13] at [[55]]the back I find six.[14] Thanks to this inequality of width, the cell comprises two apartments: the provision-store in front and the dining-room behind. The Eumenes’ spacious cupola does not permit of this arrangement; there the game is heaped up in disorder, the oldest in date promiscuously with the most recent; and each piece is merely bent, not rolled. The ascending-sheath provides a remedy for the disadvantages of this confusion.

Note also that the packing of the victuals is not the same from one end of the Odynerus’ skewerful to the other. In the cells whose provisions have not yet or have only recently been broached, I observe this detail: near the egg or the newly-hatched larva, in the part which I have just described as the dining-room, the space is not fully occupied; there are just a few grubs here, three or four, somewhat isolated from the bulk and leaving enough room to ensure the safety of either the egg or the young larva. This is the food supplied for the early meals. If there be danger in the first mouthfuls, which are the most risky of all, the life-line provides a means of withdrawal. More towards the front, the game [[56]]is piled in close-packed layers, the stack of worms is continuous.

Will the larva, now that it possesses a modicum of strength, force itself imprudently into this heap? Far from it. The victuals are consumed in due order, from the bottommost to the topmost. The larva drags towards it, to a little distance, into the dining-room, the first ring that offers, devours it without danger of being inconvenienced by the others and thus, layer by layer, consumes the batch of two dozen, always in complete security.

Let us retrace our steps and end with a brief summary. The large number of grubs provided for a single cell and their very incomplete paralysis jeopardize the security of the Wasp’s egg and of her new-born larva. How is the danger to be averted? This is the problem; and it has several solutions. The Eumenes, with her sheath, which enables the larva to climb back to the ceiling, gives us one; the Odynerus, in her turn, gives us hers, a solution no less ingenious and much more complicated.

The egg and also the newly-hatched larva have to be saved from the danger of contact with the game. A suspension-thread solves [[57]]the difficulty. Up to this point, that is the method adopted by the Eumenes; but soon the young larva, having eaten its first grub, drops off the thread that gave it a support whereby to shrink out of harm’s way. A sequence of conditions now begins, all directed towards its welfare.