In a few days the galleries are ready, especially as after some repairs those of the preceding year [[54]]are used again. Other Cerceris, as far as I know, have no fixed home, transmitted from one generation to another. True Bohemians, they establish themselves wherever the chances of their vagabond life may lead them, so long as the soil suits them. But C. tuberculata is faithful to her penates. The projecting shelf of sandstone used by its predecessors is used again; it hollows out the same layer of sand hollowed by its forbears, and, adding its own labour to theirs, obtains deep-seated retreats sometimes only visited with difficulty. The diameter of the galleries would admit a thumb, and the insect can move about easily, even when laden with the prey which we shall see it capture. Their direction is horizontal, from four to eight inches, then makes a sudden turn downward more or less obliquely, now in one direction, now in another. Except the horizontal part, and the angle of the tunnel, the direction seems to depend on the difficulties of the ground, as is proved by the windings and changes in the farthest part of this kind of canal, which is half a yard in length. At the far end are the cells, not numerous, and provisioned with five or six dead beetles. But let us leave the details of how a Cerceris builds, and turn to more wonderful facts.
[To face p. 54.
CERCERIS TUBERCULATA DRAGGING WEEVIL TO ITS BURROW
The victim chosen to feed the larvæ is a large weevil (Cleonus ophthalmicus). One sees the captor arrive, carrying the victim between its feet, body to body, head to head. It alights heavily some way from the hole to complete the journey without the aid of wings, and drags the prey laboriously with its jaws, on ground if not vertical, at least very steeply inclined, which often results in sending [[55]]captor and captive headlong to the bottom, but the indefatigable mother finally darts into her burrow, covered with dust, but with the prey of which she has never let go. If she does not find walking with such a burden easy, it is otherwise with her flight, which is surprisingly powerful, if one considers that the strong little creature is carrying a prey nearly as large as and heavier than herself. I have had the curiosity to weigh the Cerceris and her prey separately, and the first weighed 150 milligrammes, and the second about 250, almost double.
These weights speak eloquently for the vigorous huntress, and I never wearied of watching how swiftly and easily she resumed her flight, and rose out of sight with the game between her feet when approached too closely. But she did not always fly away, and then, though it was difficult to do so, and yet avoid hurting her, I would make her drop the prey by worrying and upsetting her with a straw. Then I would take possession of the victim, and the Cerceris, thus despoiled, would hunt about, go into her hole for a moment, come out, and resume the chase. In less than ten minutes the sharp-sighted insect would find a new victim, murder it and carry it off, not seldom to my profit. Eight times running have I stolen from the same individual; eight times did the indefatigable Cerceris resume her fruitless journey. Her perseverance tired out mine, and I let her keep the ninth capture.
By this means, and by breaking open cells already filled with provisions, I got nearly a hundred weevils, and in spite of what I had a right to [[56]]expect from what Léon Dufour has told us of the habits of the Cerceris bupresticida, I could not repress my astonishment at the sight of the singular collection which I had made. His Cerceris, though it limits itself to one genus, yet takes any species within that limit, but the more exclusive C. tuberculata preys exclusively on Cleonus ophthalmicus. On looking through my booty I met with but one single exception, and that belonged to a closely allied species, C. alternans—one which I never met with again in my frequent visits to the Cerceris. Later researches furnished me with a second exception, Bothynoderes albidus, and these are all. Can a specially succulent and savoury prey explain this predilection for a single species? Do the larvæ find in this unvaried diet juices which suit them peculiarly, and which they would not find elsewhere? I do not think so, and if Léon Dufour’s Cerceris hunted all the kinds of Buprestids, no doubt it was because they all have the same nutritive properties. But this must generally be the case with all the Curculionidæ; their alimentary properties must be identical, and in that case this amazing choice can only be one of size, and therefore of economy of labour and time. Our Cerceris, the giant of its race, chooses C. ophthalmicus as the largest in our district, and perhaps the commonest. But if this favourite prey fail, it must fall back upon other species, even if smaller, as is proved by the two exceptions above mentioned.
Moreover, it is by no means the only one to hunt the long-nosed class of weevils. Many other Cerceris, according to their size, strength, and the [[57]]chances of the chase, capture Curculionidæ most various in genus, species, shape, and size. It has long been known that Cerceris arenaria feeds her young with similar food. I myself have found in its burrows Sitona lineata, S. tibialis, Cneorhinus hispidus, Brachyderes gracilis, Geonemus flabellipes, Otiorhynchus maleficus. Cerceris aurita is known to prey on Otiorhynchus raucus and Phytonomus punctatus. In the larder of Cerceris ferreri I saw Phytonomus murinus, P. punctatus, Sitona lineata, Cneorhinus hispidus, Rhynchites betuleti. This weevil, which rolls up vine leaves into the shape of cigars, is sometimes of a superb metallic blue, but more usually of a splendid golden copper. I have found as many as seven of these brilliant insects laid up in one cell, and the gorgeous colours of the little heap might almost bear comparison with the jewels buried by the huntress of the Buprestids. Other species, especially the weaker, hunt smaller game, the lesser size being compensated by numbers. Thus, Cerceris quadricincta heaps in each cell some thirty Apion gravidum, but does not disdain on occasion bigger weevils, such as Sitona lineata, Phytonomus murinus. Cerceris labiata also lays up small species. Finally, the smallest Cerceris in my part of France, C. julii, hunts the least weevils, Apion gravidum and Bruchus granarius, game proportioned to its own size. To end this list of provender, let us add that some Cerceris follow other gastronomic laws, and bring up their families on Hymenoptera. Such is C. ornata. These tastes being alien to our subject, let us pass on.
We see that out of eight species of Cerceris [[58]]which lay up Coleoptera as food, seven hunt weevils and one Buprestids. What singular reason confines the chase of these Hymenoptera within such narrow limits? What are the motives of such an exclusive selection? What internal likeness is there between the Buprestids and the weevils, outwardly quite dissimilar, that both should become food for carnivorous and nearly related larvæ? No doubt between such and such a victim there are differences as to taste and nutritive qualities which the larvæ thoroughly appreciate, but there must be a far graver reason than these gastronomic considerations to explain these strange predilections.
