CHAPTER 4. MORE ENQUIRIES INTO MASON-BEES.
This chapter was to have taken the form of a letter addressed to Charles Darwin, the illustrious naturalist who now lies buried beside Newton in Westminster Abbey. It was my task to report to him the result of some experiments which he had suggested to me in the course of our correspondence: a very pleasant task, for, though facts, as I see them, disincline me to accept his theories, I have none the less the deepest veneration for his noble character and his scientific honesty. I was drafting my letter when the sad news reached me: Darwin was dead; after searching the mighty question of origins, he was now grappling with the last and darkest problem of the hereafter. (Darwin died at Down, in Kent, on the 19th of April 1882.—Translator's Note.) I therefore abandon the epistolary form, which would be unwarranted in view of that grave at Westminster. A free and impersonal statement shall set forth what I intended to relate in a more academic manner.
One thing, above all, had struck the English scientist on reading the first volume of my "Souvenirs entomologiques", namely, the Mason-bees' faculty of knowing the way back to their nests after being carried to great distances from home. What sort of compass do they employ on their return journeys? What sense guides them? The profound observer thereupon spoke of an experiment which he had always longed to make with Pigeons and which he had always neglected making, absorbed as he was by other interests. This experiment, he thought, I might attempt with my Bees. Substitute the insect for the bird; and the problem remained the same. I quote from his letter the passage referring to the trial which he wished made:
'Allow me to make a suggestion in relation to your wonderful account of insects finding their way home. I formerly wished to try it with pigeons; namely, to carry the insects in their paper cornets about a hundred paces in the opposite direction to that which you intended ultimately to carry them, but before turning round to return, to put the insects in a circular box with an axle which could be made to revolve very rapidly first in one direction and then in another, so as to destroy for a time all sense of direction in the insects. I have sometimes imagined that animals may feel in which direction they were at the first start carried.'
This method of experimenting seemed to me very ingeniously conceived. Before going west, I walk eastwards. In the darkness of their paper bags, the mere fact that I am moving them gives my prisoners a sense of the direction in which I am taking them. If nothing happened to disturb this first impression, the insect would be guided by it in returning. This would explain the homing of my Mason-bees carried to a distance of two or three miles amid strange surroundings. But, when the insects have been sufficiently impressed by their conveyance to the east, there comes the rapid twirl, first this way round, then that. Bewildered by all these revolutions first in one direction and then in another, the insect does not know that I have turned round and remains under its original impression. I am now taking it to the west, when it believes itself to be still travelling towards the east. Under the influence of this impression; the insect is bound to lose its bearings. When set free, it will fly in the opposite direction to its home, which it will never find again.
This result seemed to me the more probable inasmuch as the statements of the country-folk around me were all of a nature to confirm my hopes. Favier (The author's gardener and factotum. Cf. "The Life of the Fly": chapter 4.—Translator's Note.), the very man for this sort of information, was the first to put me on the track. He told me that, when people want to move a Cat from one farm to another at some distance, they place the animal in a bag which they twirl rapidly at the moment of starting, thus preventing the animal from returning to the house which it has quitted. Many others, besides Favier, described the same practice to me. According to them, this twirling round in a bag was an infallible expedient: the bewildered Cat never returned. I communicated what I had learnt to England, I wrote to the sage of Down and told him how the peasant had anticipated the researches of science. Charles Darwin was amazed; so was I; and we both of us almost reckoned on a success.
These preliminaries took place in the winter; I had plenty of time to prepare for the experiment which was to be made in the following May.
'Favier,' I said, one day, to my assistant, 'I shall want some of those nests. Go and ask our next-door neighbour's leave and climb to the roof of his shed, with some new tiles and some mortar, which you can fetch from the builder's. Take a dozen tiles from the roof, those with the biggest nests on them, and put the new ones in their place.'
Things were done accordingly. My neighbour assented with a good grace to the exchange of tiles, for he himself is obliged, from time to time, to demolish the work of the Mason-bee, unless he would risk seeing his roof fall in sooner or later. I was merely forestalling a repair which became more urgent every year. That same evening, I was in possession of twelve magnificent rectangular blocks of nest, each lying on the convex surface of a tile, that is to say, on the surface looking towards the inside of the shed. I had the curiosity to weigh the largest: it turned the scale at thirty-five pounds. Now the roof whence it came was covered with similar masses, adjoining one another, over a stretch of some seventy tiles. Reckoning only half the weight, so as to strike an average between the largest and the smallest lumps, we find the total weight of the Bee's masonry to amount to three-quarters of a ton. And, even so, people tell me that they have seen this beaten elsewhere. Leave the Mason-bee to her own devices, in the spot that suits her; allow the work of many generations to accumulate; and, one fine day, the roof will break down under the extra burden. Let the nests grow old; let them fall to pieces when the damp gets into them; and you will have chunks tumbling on your head big enough to crack your skull. There you see the work of a very little-known insect. (The insect is so little known that I made a serious mistake when treating of it in the first volume of these "Souvenirs." Under my erroneous denomination of Chalicodoma sicula are really comprised two species, one building its nests in our dwellings and particularly under the tiles of outhouses, the other building its nests on the branches of shrubs. The first species has received various names, which are, in order of priority: Chalicodoma pyrenaica, LEP. (Megachile); Chalicodoma pyrrhopeza, GERSTACKER; Chalicodoma rufitarsis, GIRAUD. It is a pity that the name occupying the first place should lend itself to misconception. I hesitate to apply the epithet of Pyrenean to an insect which is much less common in the Pyrenees than in my own district. I shall call it the Chalicodoma, or Mason-bee, of the Sheds. There is no objection to the use of this name in a book where the reader prefers lucidity to the tyranny of systematic entomology. The second species, that which builds its nests on the branches, is Chalicodoma rufescens, J. PEREZ. For a like reason, I shall call it the Chalicodoma of the Shrubs. I owe these corrections to the kindness of Professor Jean Perez, of Bordeaux, who is so well-versed in the lore of Wasps and Bees.—Author's Note.)
These treasures were insufficient, not in regard to quantity, but in regard to quality, for the main object which I had in view. They came from the nearest house, separated from mine by a little field planted with corn and olive-trees. I had reason to fear that the insects issuing from those nests might be hereditarily influenced by their ancestors, who had lived in the shed for many a long year. The Bee, when carried to a distance, would perhaps come back, guided by the inveterate family habit; she would find the shed of her lineal predecessors and thence, without difficulty, reach her nest. As it is the fashion nowadays to assign a prominent part to these hereditary influences, I must eliminate them from my experiments. I want strange Bees, brought from afar, whose return to the place of their birth can in no way assist their return to the nest transplanted to another site.