As this is a cleptoparasitic species, all flower visits will be for nectar only.
Celary (1995, 2007) lists the following nectar sources in Poland: Fragaria vesca, Potentilla erecta (Rosaceae); Heracleum sphondylium (Apiaceae); Veronica chamaedrys (Scrophulariaceae); Erigeron annuus, Achillea millefolium, Taraxacum officinale, Hieracium pilosella (Asteraceae).