Bramble-Bees and Others

by Jean-Henri Fabre

Besides the Bees who arrange their laying in a row, I have consulted others whose cells are grouped in a way that makes it possible to ascertain the relative order of the two sexes, though not quite so precisely. One of these is the Mason-bee of the Walls. I need not describe again her dome-shaped nest, built on a pebble, which is now so well-known to us. (Cf. "The Mason-bees": chapter 1.—Translator's Note.)

Each mother chooses her stone and works on it in solitude. She is an ungracious landowner and guards her site jealously, driving away any Mason who even looks as though she might alight on it. The inhabitants of the same nest are therefore always brothers and sisters; they are the family of one mother.

Moreover, if the stone presents a large enough surface—a condition easily fulfilled—the Mason-bee has no reason to leave the support on which she began her laying and go in search of another whereon to deposit the rest of her eggs. She is too thrifty of her time and of her mortar to involve herself in such expenditure except for grave reasons. Consequently, each nest, at least when it is new, when the Bee herself has laid the first foundations, contains the entire laying. It is a different thing when an old nest is restored and made into a place for depositing the eggs. I shall come back later to such houses.

A newly-built nest then, with rare exceptions, contains the entire laying of one female. Count the cells and we shall have the total list of the family. Their maximum number fluctuates round about fifteen. The most luxuriant series will occasionally reach as many as eighteen, though these are very scarce.

When the surface of the stone is regular all around the site of the first cell, when the mason can add to her building with the same facility in every direction, it is obvious that the groups of cells, when finished, will have the oldest in the central portion and the more recent in the surrounding portion. Because of this juxtaposition of the cells, which serve partly as a wall to those which come next, it is possible to form some estimate of the chronological order of the cells in the Chalicodoma's nest and thus to discover the sequence of the two sexes.

In winter, by which time the Bee has long been in the perfect state, I collect Chalicodoma-nests, removing them bodily from their support with a few smart sideward taps of the hammer on the pebbles. At the base of the mortar dome the cells are wide agape and display their contents. I take the cocoon from its box, open it and take note of the sex of the insect enclosed.

I should probably be accused of exaggeration if I mentioned the total number of the nests which I have gathered and the cells which I have inspected by this method during the last six or seven years. I will content myself with saying that the harvest of a single morning sometimes consisted of as many as sixty nests of the Mason-bee. I had to have help in carrying home my spoils, even though the nests were removed from their stones on the spot.

From the enormous number of nests which I have examined, I am able to state that, when the cluster is regular, the female cells occupy the centre and the male cells the edges. Where the irregularity of the pebble has prevented an even distribution around the initial point, the same rule has been observed. A male cell is never surrounded on every side by female cells: either it occupies the edges of the nest, or else it adjoins, at least on some sides, other male cells, of which the last form part of the exterior of the cluster. As the surrounding cells are obviously of a later date than the inner cells, it follows that the Mason-bee acts like the Osmiae: she begins her laying with females and ends it with males, each of the sexes forming a series of its own, independent of the other.

Some further circumstances add their testimony to that of the surrounded and surrounding cells. When the pebble projects sharply and forms a sort of dihedral angle, one of whose faces is more or less vertical and the other horizontal, this angle is a favourite site with the Mason, who thus finds greater stability for her edifice in the support given her by the double plane. These sites appear to me to be in great request with the Chalicodoma, considering the number of nests which I find thus doubly supported. In nests of this kind, all the cells, as usual, have their foundations fixed to the horizontal surface; but the first row, the row of cells first built, stands with its back against the vertical surface.

Well, these older cells, which occupy the actual edge of the dihedral angle, are always female, with the exception of those at either end of the row, which, as they belong to the outside, may be male cells. In front of this first row come others. The female cells occupy the middle portion and the male the ends. Finally, the last row, closing in the remainder, contains only male cells. The progress of the work is very visible here: the Mason has begun by attending to the central group of female cells, the first row of which occupies the dihedral angle, and has finished her task by distributing the male cells round the outside.