Renter: Existing cavities. Existing cavities such as vertical or horizontal fissures of rocks or between stones.
Nesting material: The cells, which are generally built side by side, are two-layered: the outer layer is made of rather coarsely chewed leaf pieces (e.g. Helianthemum), the inner layer consists of petals (e.g. Geranium, Linum, Lactuca)(Müller et al., 1997; Westrich, 1989, 1996).