the horizon, is incapable of
finding it at a yard's distance: I interpret the occurrence as meaning
something quite different. The proper inference appears to me to be
this: the Bee retains a rooted impression of the site occupied by the
nest and returns to it with unwearying persistence even when the nest is
gone. But she has only a very vague notion of the nest itself. She does
not recognize the masonry which she herself has erected and kneaded with
her saliva; she does not know the pollen-paste which she herself has
stored. In vain she inspects her cell, her own handiwork; she abandons
it, refusing to acknowledge it as hers, once the spot whereon the pebble
rests is changed.

Insect memory, it must be confessed, is a strange one, displaying such
lucidity in its general acquaintance with locality and such limitations
in its knowledge of the dwelling. I feel inclined to call it
topographical instinct: it grasps the map of the country and not the
beloved nest, the home itself. The Bembex-wasps (Cf. "Insect Life":
chapters 16 to 19.--Translator's Note.) have already led us to a like
conclusion. When the nest is laid open, these Wasps become wholly
indifferent to the family, to the grub writhing in agony in the sun.
They do not recognize it. What they do recognize, what they seek and
find with marvellous precision, is the site of the entrance-door of
which nothing at all is left, not even the threshold.

If any doubts remained as to the incapacity of the Mason-bee of the
Walls to know her nest other than by the place which the pebble occupies
on the ground, here is something to remove them: for the nest of one
Mason-bee, I substitute that of another, resembling it as closely as
possible in respect to both masonry and storage. This exchange and
those of which I shall speak presently are of course made in the owner's
absence. The Bee settles without hesitation in this nest which is not
hers, but which stands where the other did. If she was building, I offer
her a cell in process of building. She continues the masonry with the
same care and the same zeal as if the work already done were her
own work. If she was fetching honey and pollen, I offer her a
partly-provisioned cell. She continues her journeys, with honey in her
crop and pollen under her belly, to finish filling another's warehouse.
The Bee, therefore, does not suspect the exchange; she does not
distinguish between what is her property and what is not; she imagines