Polylectic, foraging from a wide variety of species. Free and Williams (1970) calculated the proportions of different types of pollen collected by O. bicornis, by removing and analysing faecal pellets and uneaten pollen from ten cells from trap-nests at each of six study sites in southern England. Five hundred pollen grains from each cell were identified. They discovered that only a few of the species flowering at a site were visited. At four sites the most abundant pollen collected was Quercus robur (Fagaceae); at two others it was a Ranunculus species (Ranunculaceae), and at another it was a Rubus species (Rosaceae) Traces of other pollen from one or more of these sites consisted of Acer pseudoplatanus (Aceraceae) Syringa vulgaris (Oleaceae) Aesculus hippocastanum (Hippocastanaceae) ;Trifolium repens (Fabaceae); Ilex aquifolium (Aquifoliaceae); Clematis montana (Ranunculaceae); Fragaria, Malus domestica and Crataegus monogyna (Rosaceae) Raw (1974) found that usually the cells of this bee were provisioned with over 90% of pollen from Ranunculus and Quercus. Other species were visited for nectar as Ranunculus produced very little and Quercus none at all (being a largely anemophilous species).
Else & Edwards, 2018) reports visitation in GB to Cheiranthus cheiri (Brassicaceae); Viola (Violaceae); Lotus (Fabaceae); Rhododendron (Ericaceae);Symphytum, Pentaglottis (Boraginaceae); Lamium album, Glechoma hederacea, Ajuga reptans (Lamiaceae) and Taraxacum (Asteraceae). It also seems to be an important pollinator of fruit blossoms, flying to Rubus idaeus, Prunus domestica, Pyrus pyraster and Malus (Rosaceae).
Banaszak & Romasenko (1989), copied by Stanisavljević (2000), state that the species shows a preference for pollen of Rosa, Prunus, Pyrus, Malus, Cerasus (Rosaceae); Trifolium, Caragana (Fabaceae).
Janssons (2003) lists Chelidonium (Papaveraceae), Rosa, Crataegus, Prunus (Rosaceae), Muscari (Liliaceae); Ribes (Grossulariaceae); and Tussilago (Asteraceae) as forage sources in Belgium
Ivavov et al. (2005) state that the species is polylectic, but prefers prefers Rosaceae and Brassicaceae.
Müller (cited in Knuth, 1906) reports visitation to Clematis recta, Hepatica triloba (Ranunculaceae).
Mavromoustakis (1948; 1951; 1952; 1953) reports visitation in Cyprus to Prunus avium, Amygdalus communis, Pyrus communis (Rosaceae); Sinapis alba (Brassicaceae); Calendula persica (Asteraceae); Quercus infectoria (Fagaceae); Bellevalia trifoliata (=Hyacinthus trifoliatus)(Hyacinthaceae); Asphodelus ramosus rnicrocarpus (Asphodelaceae); Vicia sp. (Fabaceae)