Nomada, Cuckoo bees are Clepto-parasites
Nomada lay their eggs in other native bee nests. Then eat the young and then the food that the other bees had provided for their young. Not nice bees. But the males of the Cuckoo bees may provide chemical mimicry of Andrena nest odors (along with a few other native bees), and although way beyond the scope of this page, the male Cuckoo bee sprays the female bee with the scent of the specific nest to provide a magic cloak so the Host bee(like Andrena) does not see the invader and allows the Nomada female to lay eggs inside the other nest. The male Nomada may just smell like the nest of the host bee. One of the theories is that the Nomada produces extra pheromones for the Female Andrena to attract a mate, but this also has not been documented.
I can't help but see the use of these bees in a political science class. The bees look so hoighty-toighty but are causing so many problems for a beneficial system of coexisting bees and plants.