visited by the Leucopsis' probe do not contain the
one thing which the insect is seeking, namely, the young larva of the
Mason-bee enclosed in its cocoon. Their contents consist of the
refuse so often met with in old Chalicodoma-nests: liquid honey left
unemployed, because the egg has perished; spoilt provisions, sometimes
mildewed, or sometimes a tarry mass; a dead larva, stiffened into a
brown cylinder; the shrivelled corpse of a perfect insect, which lacked
the strength to effect its deliverance; dust and rubbish which has
come from the exit-window afterwards closed up by the outer coating of
plaster. The odoriferous effluvia that can emanate from these relics
certainly possess very diverse characters. A sense of smell with any
subtlety at all would not be deceived by this stuff, sour, 'high,'
musty or tarry as the case may be; each compartment, according to its
contents, has a special aroma, which we might or might not be able to
perceive; and this aroma most certainly bears no resemblance to
that which we may assume the much-desired fresh larva to possess. If
nevertheless the Leucopsis does not distinguish between these various
cells and drives the probe into all of them indifferently, is this not
an evident proof that smell is no guide whatever to her in her search?
Other considerations, when I was treating of the Hairy Ammophila,
enabled me to assert that the antennae have no olfactory powers. To-day,
the frequent mistakes of the Leucopsis, whose antennae are nevertheless
constantly exploring the surface, make this conclusion absolutely
certain.

The perforator of clay nests has, so it seems to me, delivered us from
an old physiological fallacy. She would deserve studying, if for no
other result than this; but her interest is far from being exhausted.
Let us look at her from another point of view, whose full importance
will not be apparent until the end; let us speak of something which
I was very far from suspecting when I was so assiduously watching the
nests of my Mason-bees.

The same cell can receive the Leucopsis' probe a number of times, at
intervals of several days. I have said how I used to mark in black the
exact place at which the laying-implement had entered and how I wrote
the date of the operation beside it. Well, at many of these already
visited spots, concerning which I possessed the most authentic
documents, I saw the insect return a second, a third and even a
fourth time, either on the same day