As this is a cleptoparasitic species, all flower visits will be for nectar only.
The following nectar sources are reported from Germany: Daucus carota (Apidae); Achillea millefolium, Taraxacum officinale, Leontodon autumnale (Asteraceae); Berteroa incana, Sisymbrium officinale (Brassicaceae); Melilotus alba (Fabaceae); Reseda lutea (Resedaceae).(Westrich, 1989)
Celary (1991) lists the following nectar sources in Poland: Achillea millefolium, Leontodon autumnalis, Taraxacum officinalis, Hieracium pilosella (Asteraceae).
Mavromoustakis (1948)(reporting data for S. subovalis), reports nectar foraging at Ballota sp. (Lamiaceae) in Cyprus
Schmidt et al (2017) report visitation to Ranunculus sp. (Ranunculaceae) on Bornholm (Denmark)