material is a sort of dried
mud, which turns to pap on the addition of a drop of water. The two
Osmiae limit themselves to gathering natural soaked earth, mud in
short, which they allow to dry without any special preparation on their
part; and so they need deep and well-sheltered retreats, into which the
rain cannot penetrate, or the work would fall to pieces.

Latreille's Osmia uses different materials for her partitions and her
doors. She chews the leaves of some mucilaginous plant, some mallow
perhaps, and then prepares a sort of green putty with which she builds
her partitions and finally closes the entrance to the dwelling. When
she settles in the spacious cells of the Masked Anthophora (Anthophora
personata, Illig.), the entrance to the gallery, which is wide enough
to admit a man's finger, is closed with a voluminous plug of this
vegetable paste. On the earthy banks, hardened by the sun, the home is
then betrayed by the gaudy colour of the lid. It is as though the
authorities had closed the door and affixed to it their great seals of
green wax.

So far then as their building-materials are concerned, the Osmiae whom
I have been able to observe are divided into two classes: one building
compartments with mud, the other with a green-tinted vegetable putty.
To the latter belongs Latreille's Osmia. The first section includes the
Horned Osmia and the Three-horned Osmia, both so remarkable for the
horny tubercles on their faces.

The great reed of the south, Arundo donax, is often used, in the
country, for making rough garden-shelters against the mistral or just
for fences. These reeds, the ends of which are chopped off to make them
all the same length, are planted perpendicularly in the earth. I have
often explored them in the hope of finding Osmia-nests. My search has
very seldom succeeded. The failure is easily explained. The partitions
and the closing-plug of the Horned and of the Three-horned Osmia are
made, as we have seen, of a sort of mud which water instantly reduces
to pap. With the upright position of the reeds, the stopper of the
opening would receive the rain and would become diluted; the ceilings
of the storeys would fall in and the family would perish by drowning.
Therefore the Osmia, who knew of these drawbacks before I did, refuses
the reeds when they are placed perpendicularly.

The same reed is used for a second purpose. We make canisses of it,
that is to say, hurdles, which, in spring, serve for