These details leave us with one obvious conclusion, which is contrary to our original ideas, based on the unvarying character of insect industry. In constructing their jars, the Leaf-cutters, each following the taste peculiar to her species, do not make use of this or that plant to the exclusion of the others; they have no definite flora, no domain faithfully transmitted by heredity. Their pieces of leaves vary according to the surrounding vegetation; they vary in different layers of the same cell. Everything suits them, exotic or native, rare or common, provided that the bit cut out be easy to employ. It is not the general aspect of the shrub, with its fragile or bushy branches, its large or small, green or grey, dull or glossy leaves, that guides the insect: such advanced botanical knowledge does not enter into the question at all. In the thicket chosen as a pinking-establishment, the Megachile sees but one thing: leaves useful for her work. The Shrike, with his passion for plants with long, woolly sprigs, knows where to find nicely-wadded substitutes when his favourite growth, the cotton-rose, is lacking; the Megachile has much wider resources: indifferent to the plant itself, she looks only into the foliage. If she finds leaves of the proper size, of a dry texture capable of defying the damp and of a suppleness favourable to cylindrical curving, that is all she asks; and the rest does not matter. She has therefore an almost unlimited field for her labour.
These sudden and wholly unprovoked changes give cause for reflection. When my geranium-flowers were devastated, how had the obtrusive Bee, untroubled by the profound dissimilarity between the petals, snow-white here, bright scarlet there, how had she learnt her trade? Nothing tells us that she herself was not for the first time exploiting the plant from the Cape; and, if she really did have predecessors, the habit had not had time to become inveterate, considering the modern importation of the geranium. Where again did the Silvery Megachile, for whom I created an exotic shrubbery, make the acquaintance of the lopezia, which comes from Mexico? She certainly is making a first start. Never did her village or mine possess a stalk of that chilly denizen of our hot-houses. She is making a first start; and behold her straightway a graduate, versed in the art of carving unfamiliar foliage.
People often talk of the long apprenticeships served by instinct, of its gradual acquirements, of its talents, the laborious work of the ages. The Megachiles affirm the exact opposite. They tell me that the animal, though invariable in the essence of its art, is capable of innovation in the details; but at the same time they assure me that any such innovation is sudden and not gradual. Nothing prepares the innovations, nothing improves them or hands them down; otherwise a selection would long ago have been made amid the diversity of foliage; and the shrub recognized as the most serviceable, especially when it is also plentiful, would alone supply all the building-materials needed. If heredity transmitted industrial discoveries, a Megachile who thought of cutting her disks out of pomegranate-leaves and found them satisfactory ought to have instilled a liking for similar materials into her descendants; and we should this day find Leaf-cutters faithful to the pomegranate-leaves, workers who remained exclusive in their choice of the raw material. The facts refute these theories.
People also say:
'Grant us a variation, however small, in the insect's industry; and that variation, accentuated more and more, will produce a new race and finally a fixed species.'
This trifling variation is the fulcrum for which Archimedes clamoured in order to lift the world with his system of levers. The Megachiles offer us one and a very great one: the indefinite variation of their materials. What will the theorists' levers lift with this fulcrum? Why, nothing at all! Whether they cut the delicate petals of the geranium or the tough leaves of the lilac-bushes, the Leaf-cutters are and will be what they were. This is what we learn from the persistence of each species in its structural details, despite the great variety of the foliage employed.
CHAPTER 9. THE COTTON-BEES.
The evidence of the Leaf-cutters proves that a certain latitude is left to the insect in its choice of materials for the nest; and this is confirmed by the testimony of the Anthidia, the cotton-manufacturers. My district possesses five: A. Florentinum, LATR., A. diadema, LATR., A. manicatum, LATR., A. cingulatum, LATR., A. scapulare, LATR. None of them creates the refuge in which the cotton goods are manufactured. Like the Osmiae and the Leaf-cutters, they are homeless vagrants, adopting, each to her own taste, such shelter as the work of others affords. The Scapular Anthidium is loyal to the dry bramble, deprived of its pith and turned into a hollow tube by the industry of various mining Bees, among which figure, in the front rank, the Ceratinae, dwarf rivals of the Xylocopa, or Carpenter-bee, that mighty driller of rotten wood. The spacious galleries of the Masked Anthophora suit the Florentine Anthidium, the foremost member of the genus so far as size is concerned. The Diadem Anthidium considers that she has done very well if she inherits the vestibule of the Hairy-footed Anthophora, or even the ordinary burrow of the Earth-worm. Failing anything better, she may establish herself in the dilapidated dome of the Mason-bee of the Pebbles. The Manicate Anthidium shares her tastes. I have surprised the Girdled Anthidium cohabiting with a Bembex-wasp. The two occupants of the cave dug in the sand, the owner and the stranger, were living in peace, both intent upon their business. Her usual habitation is some hole or other in the crevices of a ruined wall. To these refuges, the work of others, we can add the stumps of reeds, which are as popular with the various cotton-gatherers as with the Osmiae; and, after we have mentioned a few most unexpected retreats, such as the sheath provided by a hollow brick or the labyrinth furnished by the lock of a gate, we shall have almost exhausted the list of domiciles.
Like the Osmiae and the Leaf-cutters, the Anthidium shows an urgent need of a ready-made home. She never houses herself at her own expense. Can we discover the reason? Let us first consult a few hard workers who are artificers of their own dwellings. The Anthophora digs corridors and cells in the road-side banks hardened by the sun; she does not erect, she excavates; she does not build, she clears. Toiling away with her mandibles, atom by atom, she manages to contrive the passages and chambers necessary for her eggs; and a huge business it is. She has, in addition, to polish and glaze the rough sides of her tunnels. What would happen if, after obtaining a home by dint of long-continued toil, she had next to line it with wadding, to gather the fibrous down from cottony plants and to felt it into bags suitable for the honey-paste? The hard-working Bee would not be equal to producing all these refinements. Her mining calls for too great an expenditure of time and strength to leave her the leisure for luxurious furnishing. Chambers and corridors, therefore, will remain bare.