cuckoo bee

from The Century Dictionary.

• noun A bee of the family Apidœ, and of a group variously called Cuculinœ or Nomadœ, represented by the genus Nomada.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zool.) a bee, parasitic in the larval stage in the nests of other bees, feeding either upon their food or larvae. They belong to the genera Nomada, Melecta, Epeolus, and others.