Renter: Existing cavities. The female of this species nests in almost any suitable cavity, from existing burrows in sandy soil and dead wood, to more unusual situations, including, for example, the insides of locks, a cuckoo clock and between the folds of an “Austrian blind” in a room (the bee entering the latter via a permanently open window). Crevices or fissures in crumbling mortar are frequently occupied, and it is possible that new nesting burrows can be excavated by the bee in intact, but friable mortar. In Kent, G.H.L. Dicker (pers. comm.) observed several females sharing a common entrance burrow in the decayed mortar of a wall. He counted five bees entering this burrow in under a minute and some time later three were actually queueing on the wing, whilst another emerged to leave the hole free for their entry. Nests may also be built behind ventilator grills in walls and beneath roofing tiles. On rare occasions, very large nesting aggregations occur, threatening the stability of affected masonry.
Nesting material: Cell walls, partitions and the closing plug are constructed from mud, and for this reason (and perhaps also because of the bee’s habit of nesting in walls) the species is commonly referred to as the Red Mason or Mortar Bee. In burrows where cells are arranged end to end only the transverse partitions may be built from mud, the internal surface of the burrow serving as the lateral walls to the cell. However, where more space is available a honeycomb-like aggregation of cells may result, in which entire cell walls are made from mud. Grandi (1961) describes and figures such a nest in what must have been a very broad, dead Phragmites stem; he additionally describes other nests. Nests and early stages of this species are also illustrated by Westrich (1989), O’Toole & Raw (1991), Bellmann (1995) and Müller, Krebs & Amiet (1997).
One female Osmia rufa which Raw (1974) studied, built several nests in paper drinking straws (a total of 21 cells in 20 days). The female carries a pellet of mud to the nest held in her mandibles, sometimes supported by the forelegs (see photograph in O’Toole & Raw, 1991). On its arrival at the nest, the mud is tamped into position by the prong-like clypeal projections. The nesting habits and life-history of this species are described, for example, by Raw (1972), Westrich (1989) and O’Toole & Raw (1991)(Banaszak and Romasenko, 2001; Benoist, 1931; Bonelli, 1966, 1967a, 1968; Brechtel, 1986; Friese, 1923; Grandi, 1961; Ivanov, 2006; Le Goff, 2006; Malyshev, 1937; Müller et al., 1997; Olifir, 1980; O’Toole and Raw, 1999; Raw, 1972; Schmiedeknecht, 1885-1886; Smith, 1844; Tasei, 1973; Vicens, Bosch and Blas, 1993; Westrich, 1989).