By forcing other bumblebee species to raise them
Psithyrus, known as the Cuckoo bumblebee, invades the nests of other bumblebee species, kills or subdues the resident queen, lays its own eggs, and forces the resident workers to raise the young. Psithyrus has lost the ability to collect pollen, does not exude wax from between its abdominal segments, and has a much harder exoskeleton and a longer sting than other bumblebees. In addition it does not have a worker caste, and produces only sexual males and females.
