Bumblebees (genus Bombus) have received increased academic and conservation attention with the recognition of a global pollinator crisis. However, the Bombus subgenus Psithyrus (cuckoo bumblebees), has been overlooked. Psithyrus species parasitise social Bombus species and are frequently viewed as being detrimental to their hosts. This lack of attention, combined with the taxon’s relatively low abundances and enhanced vulnerability to climate change due to its phenological dependence on Bombus, means there is an urgent conservation challenge facing Psithyrus. We found that academic literature focused on Psithyrus comprised less than 2% of the total works on Bombus, despite forming approximately 11% of Bombus species. We argue that species of the Psithyrus subgenus have key roles in the ecosystem and have been potentially overlooked bioindicator of Bombus diversity. We present evidence suggesting that the close phenological ties between Psithyrus and its hosts are being impacted by climate change. Going forward, research on Psithyrus distributions and phenology will be essential for conserving this subgenus. Additionally, addressing these areas provides broader opportunities to improve our understanding of ecosystem dynamics under climate change and their associated links with ecosystem services.