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Why do cuckoo bumblebees lay their eggs in bumblebee nests?

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Bumblebee pollination — Hymenoptera An endangered rusty patched bumblebee (*Bombus affinis*) browsing on a wild bergamot flower.

Cuckoo bumblebees (formerly classified in the genus Psithyrus and now nested within the genus Bombus) are brood parasites that lay their eggs in the nests of social bumblebees to exploit the host's resources.1

They engage in this behavior because they lack a worker caste of their own and are therefore unable to collect pollen or care for their own offspring. By infiltrating the nests of nest-building Bombus species, cuckoo bumblebees ensure that their eggs are reared by the host's "duped" workers.12

In some instances, the parasitic queen may kill the host queen, which eliminates competition for the workers' attention, allowing the parasitic larvae to be fed and cared for by the host colony. This strategy allows the cuckoo bumblebee to successfully reproduce without the energetic costs associated with building a nest or maintaining a workforce.12