Cuckoo bee
They enter the nests of pollen-collecting species, and lay their eggs in cells made by the host bee. When the cuckoo bee larva hatches it eats the host larva's pollen ball. If the female has not already done so, it kills and eats the host larva. In a few cases the invading female stays in the host nest and lays many eggs. Sometimes it kills the host queen and replaces her. Species like that are often called 'social parasites'. Some are referred to as 'brood parasites'. There is a whole subfamily of bees which do this, the Nomadinae (nomad bees).