Bombus rupestris Fabricius 1793

Bombus rupestris Fabricius, 1793 Conservation status EN Distribution Bombus rupestris has a large distribution in the West Palearctic (Rasmont et al. 2021). In Belgium, the species is absent from many localities where it was once found (Folschweiller 2020), especially in the Hainaut province. Most of its subsisting locations are concentrated in the northern and oriental parts of its Belgian distribution (Campine, Ardenne and Belgian Lorraine). It is noteworthy that, even historically, B. rupestris has never been a relatively abundant species in the country. The males of the species are largely associated with thistles and their regression could have acted as a major factor of decline in the species. Besides, climate change is expected to induce large-scale reductions of its European range by 2080-2100 (Rasmont et al. 2015, Ghisbain et al. 2024). Notes Bombus rupestris is a socially parasitic bumblebee species. It parasitiszes the nest of Bombus lapidarius, a very common species both across Europe and in Belgium (Rasmont et al. 2021). The species does not seem to be strongly associated with specific habitat types, although it is largely absent from urbanised areas (Folschweiller 2020). Diagnosis In Belgium, the females of B. rupestris (Fig. 8) can be confused with other species of black bumblebees with a ‘ red tail’, such as B. lapidarius, B. ruderarius, B. soroeensis and B. cullumanus (although the latter is thought to have fully extinct from the country). However, females of B. rupestris can be separated from all other concolour bumblebees by the presence of a high density of hairs on the metatibia. This feature is typical of the parasitic bumblebees of the subgenus Psithyrus, that lack a corbicula for collecting pollen. The males of B. rupestris can be differentiated from the males of all other bumblebee species on the basis of the morphology of their genitalia (drawn in Rasmont et al. 2021).