Cuckoo bumblebees, as their name suggests, take over the nests of ‘true’ bumblebees. The Cuckoo queen enter their host nest, and kill the existing queen. The remaining workers then rear the cuckoo’s young. The cuckoo bumbles, of which there are six species in Ireland, can be difficult enough to distinguish from true bumbles. However one distinguishing feature is the lack of a pollen basket on the back leg of the bee.
The photo below is of a forest cuckoo bumblebee. They appear to be having a good year with sightings in Mayo and Clare in the last couple of weeks
They are probably one of the easier species to identify with their large white tails and their single yellow band.
Forest Cuckoo bumblebee Bombus sylvestris
Note: no pollen basket on bee on left but Garden bumblebee on right (a true bumblebee) the pollen basket is obvious.