I will add but a few words to the history of the C. bupresticida. This Hymenopteron, common in the Landes, as we have heard, seems to be rare in the department of Vaucluse. It is only at long intervals that I have met with it, in autumn, and always isolated specimens, on the spiny heads of Eryngium campestre, in the environs of Avignon or round Orange and Carpentras. In the latter spot, so favourable to burrowing hymenoptera, from its sandy soil of Mollasse, I had the good fortune, not indeed of being present at the exhumation of such entomological riches as Léon Dufour describes, but of finding some old nests which I feel certain belonged to Cerceris bupresticida, from the shape of the cocoons, the kind of provender stored up, and the existence of the Hymenopteron in the neighbourhood. These nests, hollowed in a very friable sandstone, called safre in those parts, were filled with remains of beetles, easily recognised, and consisting of detached wing-cases, empty corslets, and whole feet. Now these remains of the larva’s feast all belonged to one species, and this was a Buprestis, Sphænoptera geminata. Thus from the west to the east of France, from the department of the Landes to Vaucluse, the Cerceris remains faithful to its favourite prey; longitude does not affect its predilections, a hunter of Buprestids among the maritime pines of the ocean sand-hills, it is equally so amid the evergreen oaks and olives of Provence. [[50]]The species is changed according to place, climate, and vegetation—causes influencing greatly the insect population, but the Cerceris keeps to its chosen genus, the Buprestis. For what strange reason? That is what I shall try to demonstrate. [[51]]
[1] The beetles dug up belonged to the following species:—Buprestis octoguttata, B. bifasciata, B. pruni, B. tarda, B. biguttata, B. micans, B. flavomaculata, B. chrysostigma, B. novem-maculata. [↑]
IV
CERCERIS TUBERCULATA
With my mind full of the great deeds of the Buprestis hunter, I watched for an opportunity of observing in my turn the labours of the Cerceris, and I watched so closely that finally I got my chance. True, it was not the Hymenopteron celebrated by Dufour, with such sumptuous provisions that when dug up they made one think of the powder from a nugget broken by the miner’s pickaxe in some gold field: it was a closely related species, a giant brigand which contents itself with more modest prey—in short, Cerceris tuberculata or C. major, the largest and strongest of the genus.
The last fortnight in September is the time when our Hymenopteron makes its burrows, and buries in the depths the prey destined for its brood. The position of the domicile, always sagaciously chosen, is governed by those mysterious laws varying with the species, but unchangeable for any one of them. The Cerceris of Léon Dufour requires a horizontal, beaten, compact soil, like that of a path, to avoid landslips and changes which would ruin its gallery with the first rain. Ours, on the [[52]]contrary, selects vertical ground. By this slight architectural modification she avoids most of the dangers which might threaten her tunnel; therefore she is not particular as to the nature of the soil, and hollows her gallery either in friable earth with a little clay, or in the crumbling soil of the Mollasse, which makes the labour of excavation much easier. The only indispensable condition seems to be that the soil should be dry, and exposed to the sun for the greater part of the day. It is therefore in the steep bank along a road, and in the sides of hollows made by rain in the sandy Mollasse, that our Hymenopteron makes its abode. Such conditions are frequent near Carpentras in what is known as the hollow way, and it is there that I have found C. tuberculata in the greatest abundance, and have collected most of the facts relating to its history.
It is not enough to choose this vertical situation; other precautions are taken to guard against the already advanced season. If some bit of hard sandstone project like a shelf, or if a hole the size of one’s fist should have been hollowed naturally in the ground, it will be under this shelter or in this cavity that the gallery is made, a natural vestibule being thus added by the Cerceris to its own edifice. Although there is no kind of community among them, these insects like to associate in small parties, and I have always found their nests in groups of about ten, with orifices, though usually far apart, sometimes touching.
When the sun shines it is wonderful to see the ways of these hard-working miners. Some patiently extract bits of gravel from the bottom of a hole [[53]]with their mandibles, and push out the heavy mass; others scratch the walls of their tunnel with the sharp rakes of their tarsi, forming a heap of rubbish which they sweep out backward, and send sliding down the steep incline in long dusty streams. It was these periodical sand waves thrown out of galleries in process of construction which betrayed my first Cerceris, and led to the discovery of the nests. Others, either weary, or having completed their hard task, rested and polished their antennæ and wings under the natural caves which usually protect their dwelling, or else sat motionless at the mouth of their holes, only displaying their wide, square faces, barred with yellow and black. Others again were flying with a deep hum on the bushes near the cochineal oak, where the males, always on the watch near the burrows in process of construction, speedily join them. Couples form, often troubled by the arrival of a second male, which tries to supplant the happy possessor. The humming grows menacing, quarrels begin, and often both males roll in the dust until one acknowledges the superiority of his rival. Not far off the female waits with indifference the upshot of the struggle, accepting finally the male bestowed on her by the chances of the fight, and the pair fly out of sight to seek peace in some distant thicket. Here the part of the male ends. One half smaller than the females, they prowl about the burrows but never enter, and never take any part in the hard work of excavation, or that perhaps yet harder of provisioning the cells.