The Chalicodoma of the Walls employs the same building-methods as Eumenes Amadei: in the courses of cement, she fixes, on the outside, small stones of minor bulk. Her work begins by being a turret of rustic art, not without a certain prettiness; then, when the cells are placed side by side, the whole construction degenerates into a lump governed apparently by no architectural rule. Moreover, the Mason-bee covers her mass of cells with a thick layer of cement, which conceals the original rockwork edifice. The Eumenes does not resort to this general coating: her building is too strong to need it; she leaves the pebbly facings uncovered, as well as the entrances to the cells. The two sorts of nests, though constructed of similar materials, are therefore easily distinguished.
The Eumenes’ cupola is a piece of artist’s work; and the artist would be sorry to hide [[10]]her masterpiece under whitewash. I crave forgiveness for a suggestion which I advance with all the reserve befitting so delicate a subject. Would it not be possible for the cromlech-builder to take a pride in her handiwork, to look upon it with some affection and to feel gratified by this evidence of her cleverness? Might there not be an insect science of æsthetics? I seem at least to catch a glimpse, in the Eumenes, of a propensity to beautify her product. The nest must be first and foremost a solid habitation, an inviolable stronghold; but, should ornament intervene without jeopardizing the power of resistance, will the worker remain indifferent to it? Who could say?
Let us set forth the facts. The orifice at the top, if left as a mere hole, would suit the purpose quite as well as an elaborate door: the insect would lose nothing in regard to facilities for coming and going and would gain by shortening the labour. Yet we find, on the contrary, the mouth of an amphora, gracefully curved, worthy of a potter’s wheel. Choice cement and careful work are needed for the confection of its slender, funnelled shaft. Why this nice finish, [[11]]if the builder be wholly absorbed in the solidity of her work?
Here is another detail: among the bits of gravel employed for the outer covering of the cupola, grains of quartz predominate. They are polished and translucent; they glitter slightly and please the eye. Why are these little pebbles preferred to chips of limestone, when both materials exist in equal abundance around the nest?
A yet more remarkable feature: we find pretty often, encrusted on the dome, a few tiny empty Snail-shells, bleached by the sun. The species usually selected by the Eumenes is one of the smaller Helices, Helix strigata, frequent on our parched slopes. I have seen nests where this Helix took the place of pebbles almost entirely. They were like boxes made of shells, the work of a patient hand.
A comparison suggests itself. Certain Australian birds, notably the Bower-birds, build themselves covered walks or arbours with interwoven twigs and decorate the two entrances to the portico by strewing the threshold with anything that they can find in the shape of glittering, polished or bright-coloured objects. Every doorsill is a cabinet [[12]]of curiosities where the collector gathers smooth pebbles, variegated shells, empty Snail-shells, Parrots’ feathers, bones that have come to look like sticks of ivory. Even the odds and ends mislaid by man find a home in the bird’s museum, where we see pipe-stems, brass buttons, strips of cotton stuff and stone axe-heads.
The collection at either entrance to the bower is large enough to fill half a bushel. As these things are of no use to the bird, its only motive for accumulating them must be an art-lover’s hobby. Our common Magpie has similar tastes: any shiny thing that he comes upon he picks up, hides and hoards.
Well, the Eumenes, who shares this passion for bright pebbles and empty Snail-shells, is the Bower-bird of the insect world; but she is a more practical collector, knows how to combine the useful and the ornamental and employs her discoveries in the construction of her nest, which is both a fortress and a museum. When she finds bits of translucent quartz, she rejects everything else: the building will be all the prettier for them. When she comes across a little white shell, she hastens to beautify her dome with it; should fortune smile and empty Snail-shells [[13]]abound, she encrusts the whole fabric with them, until it becomes the supreme expression of her artistic taste. Is this so or not? Who shall decide?
The nest of Eumenes pomiformis is the size of an average cherry and constructed of pure mortar, without any outer pebblework. Its shape is exactly similar to that which we have just described. When built upon a large enough horizontal base, it is a dome with a central neck, funnelled like the mouth of an urn. But, when the foundation is reduced to a mere point, as on the twig of a shrub, the nest becomes a spherical capsule, always, of course, surmounted by a neck. It is then a miniature specimen of exotic pottery, a big-bellied alcarraza. Its thickness is very slight, less than that of a sheet of paper; it crushes under the least finger-pressure. The outside is not quite even. It displays wrinkles and seams, due to the different courses of mortar, or else knotty projections distributed almost concentrically.
Both Wasps accumulate caterpillars in their coffers, whether domes or jars. Let us give an abstract of the bill of fare. These documents, for all their dryness, possess a value: they will enable whoso [[14]]cares to interest himself in the Eumenes to perceive to what extent instinct modifies the diet, according to place and season. The food is plentiful but lacks variety. It consists of tiny caterpillars, by which I mean the grubs of small Butterflies or Moths. This is proclaimed by the structure, for we observe the usual caterpillar organism in the prey selected by either Wasp. The body is composed of twelve segments, not including the head. The first three have true legs, the next two are legless, then come four segments with prolegs, two legless segments and, lastly, a terminal segment with prolegs. It is exactly the same organization which we saw in the Ammophila’s Grey Worm.