As this is a cleptoparasitic species, all flower visits will be for nectar only.
Flowers visited in UK (Else & Edwards, 2018): Heracleum, Pimpinella saxifraga, (Apiaceae); Tripleurospermum, Picris (Asteraceae).
The following plant species are listed as nectar sources in Poland: Daucus carota (Apiaceae); Jasione montana (Campanulaceae); Achillea millfolium, Senecio jacobaea (Asteraceae)(Celary, 1999; Celary & Wisniowski, 2001).