As this is a cleptoparasitic species, all flower visits will be for nectar only.
The following nectar sources are cited for Germany: Ballota nigra, Ajuga reptans, Nepeta cataria, Stachys recta (Lamiaceae); Lycium barbarum (Solanaceae); Echium vulgare (Boraginaceae); Knautia arvensis (Dipsacaceae) (Westrich, 1989)
Celary (1990) lists the following nectar sources in Poland: Anchusa sp. (Boraginaceae); Marrubium sp., Hyssopus officinalis (Lamiaceae); Carduus sp., Cirsium sp. (Asteraceae).