Renter: Existing cavities. Typical nests are built within exit burrows of the cerambycid beetle Rhagium inquisitor, in the thicker, corky bark of old pine trees which are standing in sunny positions (dead bees within these nests confirmed them as belonging to O.uncinata) (M. Edwards, 1999 and 2001). The cells vary in number from one to at least three, the cell partitions being constructed from leaf mastic. The full fed larva spins a reddish-brown cocoon consisting of two separate layers. Photographs of opened nests in Pinus sylvestris bark, with cells containing cocoons, are provided by M. Edwards (2001). It is assumed that the species over-winters as an adult within the sealed cocoon, emerging for the first time the following spring or early summer. However, an obligate two-year life cycle may exist (as occurs with the closely related O. inermis), with the first winter (and perhaps as many as several sequencial winters) spent as a prepupa, and the fllowing winter being passed as an adult.
F.K. Stöckhert (1933) similarly reports that in Germany the bee nests in bark on trunks and stumps of pines,and sometimes in small detached pieces lying on the ground. Also in Germany, P. Westrich (pers. comm.) has found the bee nesting in trap nests in montane forests.
Nesting material: Cell partitions and nest plug are made of chewed leaves. (Amiet et al., 2004; Banaszak and Romasenko, 2001; Friese, 1923; Stoeckhert, 1933; Westrich, 1989; G. Else, unpublished manuscript)