As this is a cleptoparasitic species, all flower visits will be for nectar only.
Flowers visited for nectar: Cynoglossum officinale (Boraginaceae)appears to be the only British record (Nevinson, 1902).
In the Netherlands it visits Lithospermum officinale (Boraginaceae); Lamium album and Nepeta cataria (Lamiaceae) for nectar (Lieftinck, 1980).
Celary (1990) lists the following nectar sources in Poland: Salix sp. (Salicaceae); Trifolium sp., Lotus corniculatus (Fabaceae); Ajuga sp., Glechoma hederaceae (Lamiaceae).