Renter: Existing cavities. Nests in existing cavities (eg beetle emergence holes).
Very little is apparently known about the nesting habits of this species (Koster, 1986), although V. Lefeber states that in the Netherlands he has reared it from nests in holes in wooden posts and Crataegus wood (pers.comm.); Peeters, Raemakers & Smit (1999) additionally list nests found in holes in Salix wood. An opened nest showing a series of consecutively arranged cells is illustrated by Müller, Krebs & Amiet (1997).