[2] This distribution is fragmented, and it is likely that B. inexspectatus is a relictual species that once occurred more widely but became limited to mountaintops as conditions changed.

It does not produce its own worker bees and cannot maintain its own colony; instead, individuals live inside the nest of another bumblebee species.

This species has apparently evolved obligate parasitism separately from the few other taxa that practice it, such as the cuckoo bees (subgenus Psithyrus).

The bee is already rare with geographically separated populations, and available high-mountain habitat is shrinking due to climate change.

Its parasitic lifestyle also makes it susceptible to indirect damage from population reductions in its host species.