Cleptoparasitic: Hosts; This bee has long been known in Britain as a cleptoparasite of Hoplitis claviventris (F. Smith, 1876; E. Saunders, 1896a; R.C.L. Perkins, 1923; Hallett, 1928; Chambers, 1949; pers. obs.) having been reared on many occasions from Rubus, Rosa and Senecio stem-nests of this species.
On the continent two Hoplitis species have been reported as hosts: H. claviventris (Friese, 1895b; Höpper, 1904b; Jørgensen, 1921; Enslin, 1925; Bischoff, 1927; van der Zanden, 1982; Banaszak & Romasenko, 1998) and H. leucomelana (Friese, 1895b; Höpper, 1904b; E. Stöckhert, 1919; Jørgensen, 1921; Enslin, 1925; Bischoff, 1927; Micheli, 1935; van der Zanden, 1982 and Banaszak & Romasenko, 1998). H. leucomelana is only doubtfully native to Britain. The mature larva and cocoon of S. ornatula have been described and illustrated by Micheli (1935), and cells of H. claviventris occupied by of both host and cleptoparasite have been figured by Höpper (1904b) and Müller Krebs & Amiet, (1997). Westrich (1989) also cites Osmia caerulescens as a host.
Banaszak & Romasenko (1998) additionally list as hosts Hoplitis tridentata, Osmia maritima, Ceratina cucurbitina. None of these three species has been found in Britain, and the relationship between them and Stelis ornatula requires confirmation.