f the other Osmiae, of the Chalicodomae and of the
Bees in general were all traceable to a common law. It seemed to me that
the arrangement in a succession first of females and then of males did
not account for everything. There must be something more. And I was
right: that arrangement in series is only a tiny fraction of the
reality, which is remarkable in a very different way. This is what I am
going to prove by experiment.

CHAPTER 4. THE MOTHER DECIDES THE SEX OF THE EGG.

I will begin with the Mason-bee of the Pebbles. (This is the same
insect as the Mason-bee of the Walls. Cf. "The Mason-bees":
passim.--Translator's Note.) The old nests are often used, when they are
in good enough repair. Early in the season the mothers quarrel fiercely
over them; and, when one of the Bees has taken possession of the coveted
dome, she drives any stranger away from it. The old house is far from
being a ruin, only it is perforated with as many holes as it once had
occupants. The work of restoration is no great matter. The heap of earth
due to the destruction of the lid by the outgoing tenant is taken out of
the cell and flung away at a distance, atom by atom. The remnants of
the cocoon are also thrown away, but not always, for the delicate silken
wrapper sometimes adheres closely to the masonry.

The victualling of the renovated cell is now begun. Next comes the
laying; and lastly the orifice is sealed with a mortar plug. A second
cell is utilized in the same way, followed by a third and so on, one
after the other, as long as any remain unoccupied and the mother's
ovaries are not exhausted. Finally, the dome receives, mainly over the
apertures already plugged, a coat of plaster which makes the nest look
like new. If she has not finished her laying, the mother goes in search
of other old nests to complete it. Perhaps she does not decide to found
a new establishment except when she can find no second-hand dwellings,
which mean a great economy of time and labour. In short, among the
countless number of nests which I have collected, I find many more
ancient than recent ones.

How shall we distinguish one from the other? The outward aspect tells
you nothing, owing to the great care taken by the Mason to restore the
surface of the old dwelling equal to new. To resist the rigours of the
winter, this surface must be impregnable. The mother knows that and
therefore repairs the dome. Inside, it is another matter: the old nest
stands