Renter: Existing cavities. Nests in existing cavities (eg beetle emergence holes).
Nest illustrated by Westrich (1989). Nests are established in dead Rubus stems (F. Smith, 1855a), in hard clay banks, and occasionally in the mortar of masonry (V.R. Perkins, 1892). A large nesting aggregation has been observed in recent years in the vertical face of a sandpit near Oxford (O'Toole & Raw, 1991). In the latter site O'Toole found that the females either excavated their own nest burrows, or occupied the vacated burrows of old Colletes daviesanus nests (in these adding their own cell linings to those of the former occupants).
It has also been reared from dead, pithy stems on the continent: Rubus and Rosa (Janvier, 1972). In the Netherlands, Peeters, Raemakers & Smit (1999) report that, in addition to nesting in dry stems, H. signatus will also occupy old nests of various wall-nesting wasps and bees.
Weissmann et al (2017) report that in the Azores, the species will nest in existing cavities (eg twigs, earth, abandoned nests of other hymenoptera)
sometimes in dense aggregations