As this is a cleptoparasitic species, all flower visits will be for nectar only.
Westrich (1989) lists the following plant species as nectar sources: Salix (Salicaceae); Potentilla verna (Rosaceae); Frangula alnus (Rhamnaceae); Sedum acre (Crassulaceae); Origanum vulgare (Lamiaceae); Melilotus alba (Fabaceae); Cirsium arvense, Taraxacum officinale (Asteraceae).
Smit (2004) lists Tussilago farfara (Asteraceae) as a nectar source.
Monsevicius (2004) lists Melilotus albus (Fabaceae) as a nectar source in Lithuania.