Here is an example: in July, I split some bramble-stems in which Osmia tridentata has built her nests. In the long series of cells, the lower already hold the Osmia's cocoons, while the upper contain the larva which has nearly finished consuming its provisions and the topmost show the victuals untouched, with the Osmia's egg upon them. It is a cylindrical egg, rounded at both extremities, of a transparent white and measuring four to five millimetres in length. (.156 to.195 inch.—Translator's Note.) It lies slantwise, one end of it resting on the food and the other sticking up at some distance above the honey. Now, by multiplying my visits to the fresh cells, I have on several occasions made a very valuable discovery. On the free end of the Osmia's egg, another egg is fixed; an egg quite different in shape, white and transparent like the first, but much smaller and narrower, blunt at one end and tapering into a rather sharp point at the other. It is two millimetres long by half a millimetre wide. (.078 and.019 inch.—Translator's Note.) It is undeniably the egg of a parasite, a parasite which compels my attention by its curious method of installing its family.
It opens before the Osmia's egg. The tiny grub, as soon as it is born, begins to drain the rival egg, of which it occupied the top part, high up above the honey. The extermination soon becomes perceptible. You can see the Osmia's egg turning muddy, losing its brilliancy, becoming limp and wrinkled. In twenty-four hours, it is nothing but an empty sheath, a crumpled bit of skin. All competition is now removed; the parasite is the master of the house. The young grub, when demolishing the egg, was active enough: it explored the dangerous thing which had to be got rid of quickly, it raised its head to select and multiply the attacking-points. Now, lying at full length on the surface of the honey, it no longer shifts its position; but the undulations of the digestive canal betray its greedy absorption of the Osmia's store of food. The provisions are finished in a fortnight and the cocoon is woven. It is a fairly firm ovoid, of a very dark-brown colour, two characteristics which at once distinguish it from the Osmia's pale, cylindrical cocoon. The hatching takes place in April or May. The puzzle is solved at last: the Osmia's parasite is a Wasp called the Spotted Sapyga (Sapyga punctata, V.L.)
Now where are we to class this Wasp, a true parasite in the strict sense of the word, that is to say, a consumer of others' provisions. Her general appearance and her structure make it clear to any eye more or less familiar with entomological shapes that she belongs to a species akin to that of the Scoliae. Moreover, the masters of classification, so scrupulous in their comparison of characteristics, agree in placing the Sapygae immediately after the Scoliae and a little before the Mutillae. The Scoliae feed their grubs on prey; so do the Mutillae. The Osmia's parasite, therefore, if it really derives from a transformed ancestor, is descended from a flesh-eater, though it is now an eater of honey. The Wolf does more than become a Sheep: he turns himself into a sweet-tooth.
'You will never get an apple-tree out of an acorn,' Franklin tells us, with that homely common-sense of his.
In this case, the passion for jam must have sprung from a love of venison. Any theory might well be deficient in balance when it leads to such vagaries as this.
I should have to write a volume if I would go on setting forth my doubts. I have said enough for the moment. Man, the insatiable enquirer, hands down from age to age his questions about the whys and wherefores of origins. Answer follows answer, is proclaimed true to-day and recognized as false tomorrow; and the goddess Isis continues veiled.
CHAPTER 10. THE TRIBULATIONS OF THE MASON-BEE.
To illustrate the methods of those who batten on others' goods, the plunderers who know no rest till they have wrought the destruction of the worker, it would be difficult to find a better instance than the tribulations suffered by the Chalicodoma of the Walls. The Mason who builds on the pebbles may fairly boast of being an industrious workwoman. Throughout the month of May, we see her black squads, in the full heat of the sun, digging with busy teeth in the mortar-quarry of the road hard by. So great is her zeal that she hardly moves out of the way of the passer-by; more than one allows herself to be crushed underfoot, absorbed as she is in collecting her cement.
The hardest and driest spots, which still retain the compactness imparted by the steam-roller, are the favourite veins; and the work of making the pellet is slow and painful. It is scraped up atom by atom; and, by means of saliva, turned into mortar then and there. When it is all well kneaded and there is enough to make a load, the Mason sets off with an impetuous flight, in a straight line, and makes for her pebble, a few hundred paces away. The trowel of fresh mortar is soon spent, either in adding another storey to the turret-shaped edifice, or in cementing into the wall lumps of gravel that give it greater solidity. The journeys in search of cement are renewed until the structure attains the regulation height. Without a moment's rest, the Bee returns a hundred times to the stone-yard, always to the one spot recognized as excellent.