As this is a cleptoparasitic species, all flower visits will be for nectar only.
Nectar sources in Germany include: Thymus pulegioides (Lamiaceae), Jasione montana (Campanulaceae); Sedum reflexum (Crassulaceae); Reseda lutea (Resedaceae); Rubus fruticosus (Rosaceae); Hieracium (Asteraceae); Epilobium angustifolium (Onagraceae) (Westrich, 1989)
In addition to the species listed by Westrich (1989), Kasparek (2015) also lists Centaurea virgata, Hieracium umbellatum (Asteraceae); Lotus corniculatus, Trifolium aureum (Fabaceae); Potentilla argentea (Rosaceae).
Mavromoustakis (1948; 1952) notes the following nectar sources in Cyprus: Mentha longifolia, Teucrium polium micropodioides, Marrubium vulgare apolum Lamiaceae; Calycotome villosa (Fabaceae); Heliotropium europeum, Heliotropium villosum (Boraginaceae); Limonium (=Statice) virgata (Plumbaginaceae).
Popov (1944) reported nectaring at Limonium (=Statice) virgata (Plumbaginaceae) and Rubus sp. (Rosaceae)
Fateryga (2017) reports nectaring at Glycyrrhiza glabra (Fabaceae) in the Krasnodar region of the North Caucasus (Russia).