What action does the female cuckoo bumblebee take regarding an established nest of a social species?

Invades and subdues the host queen

The nesting habit of the cuckoo bumblebee female is characterized by invasion rather than construction. When a social bumblebee queen emerges from hibernation, she must expend significant energy finding a cavity, building cells, and nursing her first larvae solo. Cuckoo females completely bypass this demanding initial phase by seeking out an active host nest belonging to a social bumblebee species. Once located, the parasitic female engages in a physical confrontation, often overpowering, paralyzing, or killing the existing host queen. This hostile takeover is necessary for the cuckoo to secure the infrastructure and labor force provided by the unsuspecting host workers, who are subsequently tricked into raising the parasitic brood.