Renter: Existing cavities: insect burrows in dead wood and drilled borings in wooden blocks; hollow stems (e.g. Phragmites); insect burrows in the ground; empty snail shell (Cepaea) in the fissure of a stone wall; abandoned cells in exposed nests of Chalicodoma.
LeGoff (pers.comm) reports occasional nesting in large snail shells lodged in holes in walls. He notes Eobania vermiculata and Helix aspersa (in the Vaucluse)
Nesting material: Cell partitions and nest plug are made of mud. (Benoist, 1931; O’Toole and Raw, 1991; Vicens, Bosch and Blas, 1993, 1994; A. Müller, personal observation)