The evidence of the Shrike, confirmed by that of all the other workers--weavers, basket-makers or woodcutters--whom we may care to call as witnesses, shows us what a large part must be assigned to discernment in the bird's choice of materials for its nest. Is the insect as highly gifted? When it works with vegetable matter, is it exclusive in its tastes? Does it know only one definite plant, its special province? Or has it, for employment in its manufactures, a varied flora, in which its discernment exercises a free choice? For answers to these questions we may look, above all, to the Leaf-cutting Bees, the Megachiles. Reaumur has told the story of their industry in detail; and I refer the reader who wishes for further particulars to the master's Memoirs.
The man who knows how to use his eyes in his garden will observe, some day or other, a number of curious holes in the leaves of his lilac- and rose-trees, some of them round, some oval, as if idle but skilful hands had been at work with the pinking-iron. In some places, there is scarcely anything but the veins of the leaves left. The author of the mischief is a grey-clad Bee, a Megachile. For scissors, she has her mandibles; for compasses, producing now an oval and anon a circle, she has her eye and the pivot of her body. The pieces cut out are made into thimble-shaped wallets, destined to contain the honey and the egg: the larger, oval pieces supply the floor and sides; the smaller, round pieces are reserved for the lid. A row of these thimbles, placed one on top of the other, up to a dozen or more, though often there are less: that is, roughly, the structure of the Leaf-cutter's nest.
When taken out of the recess in which the mother has manufactured it, the cylinder of cells seems to be an indivisible whole, a sort of tunnel obtained by lining with leaves some gallery dug underground.
The real thing does not correspond with its appearance: under the least pressure of the fingers, the cylinder breaks up into equal sections, which are so many compartments independent of their neighbours as regards both floor and lid. This spontaneous break up shows us how the work is done. The method agrees with those adopted by the other Bees. Instead of a general scabbard of leaves, afterwards subdivided into compartments by transverse partitions, the Megachile constructs a string of separate wallets, each of which is finished before the next is begun.
A structure of this sort needs a sheath to keep the pieces in place while giving them the proper shape. The bag of leaves, in fact, as turned out by the worker, lacks stability; its numerous pieces, not glued together, but simply placed one after the other, come apart and give way as soon as they lose the support of the tunnel that keeps them united. Later, when it spins its cocoon, the larva infuses a little of its fluid silk into the gaps and solders the pieces to one another, especially the inner ones, so much so that the insecure bag in due course becomes a solid casket whose component parts it is no longer possible to separate entirely.
The protective sheath, which is also a framework, is not the work of the mother. Like the great majority of the Osmiae, the Megachiles do not understand the art of making themselves a home straight away:
they want a borrowed lodging, which may vary considerably in character. The deserted galleries of the Anthophorae, the burrows of the fat Earth-worms, the tunnels bored in the trunks of trees by the larva of the Cerambyx-beetle (The Capricorn, the essay on which has not yet been published in English.--Translator's Note.), the ruined dwellings of the Mason-bee of the Pebbles, the Snail-shell nests of the Three-horned Osmia, reed-stumps, when these are handy, and crevices in the walls are all so many homes for the Leaf-cutters, who choose this or that establishment according to the tastes of their particular genus.
For the sake of clearness, let us cease generalizing and direct our attention to a definite species. I first selected the White-girdled Leaf-cutter (Megachile albocincta, PEREZ), not on account of any exceptional peculiarities, but solely because this is the Bee most often mentioned in my notes. Her customary dwelling is the tunnel of an Earth-worm opening on some clay bank. Whether perpendicular or slanting, this tunnel runs down to an indefinite depth, where the climate would be too damp for the Bee. Besides, when the time comes for the hatching of the adult insect, its emergence would be fraught with peril if it had to climb up from a deep pit through crumbling rubbish. The Leaf-cutter, therefore, uses only the front portion of the Worm's gallery, two decimetres at most. (7.8 inches.--Translator's Note.) What is to be done with the rest of the tunnel?
It is an ascending shaft, tempting to an enemy; and some underground ravager might come this way and destroy the nest by attacking the row of cells at the back.
The danger is foreseen. Before fashioning her first honey-bag, the Bee blocks the passage with a strong barricade composed of the only materials used in the Leaf-cutter's guild. Fragments of leaves are piled up in no particular order, but in sufficient quantities to make a serious obstacle. It is not unusual to find in the leafy rampart some dozens of pieces rolled into screws and fitting into one another like a stack of cylindrical wafers. For this work of fortification, artistic refinement seems superfluous; at any rate, the pieces of leaves are for the most part irregular. You can see that the insect has cut them out hurriedly, unmethodically and on a different pattern from that of the pieces intended for the cells.
