If these favourite haunts are lacking, then a hiding-place in the wall, a round hole in some bit of wood, the tube of a reed, the spiral of a dead Snail under a heap of stones are adopted, according to the tastes of the several species.

The retreat selected is divided into chambers by partition-walls, after which the entrance to the dwelling receives a massive seal.

That is the sum-total of the building done.
For this plasterer's rather than mason's work, the Horned and the Three-horned Osmia employ soft earth.

This 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.