A Brood parasite. All flower visits will be for nectar only
In Spain, Ornosa & Ortiz-Sánchez (2004) list the following plant families as providing forage: Boraginaceae, Rosaceae, Dipsacaceae and Lamiaceae.
Host:
A. Muller (2005) reports that B. inexspectatus is a brood parasite of B. ruderarius, and found a freshly emerged female in the nest of its host in Switzerland.
The simultaneous occurrence of freshly hatched sexuals of both B. ruderarius and B. inexspectatus in the same nest indicates that the females of both the host and the parasite must have coexisted for some time within the colony. Obviously, the invasion of the nest by B. inexspectatus did not completely stop the production of sexuals in B. ruderarius. Coexistence of host queen and social parasite and rearing of host sexuals also in the presence of the parasite, though often in reduced numbers, have repeatedly been observed in bumblebee colonies invaded by Psithyrus (Fisher, 1987, 1988).