Desert Cuckoo Bee frenetically gathering nectar. Size: 10mm

Cuckoo Bees are parasites, in that the female cuckoo bee lays her eggs in the nest of other bees, primarily digger bees and Andrenids.  Cuckoos are also said to be kleptoparasites, stealing honey and pollen collected by others. Cuckoo bees lack any pollen-transporting apparatus (the scopa). Look for cuckoo bees flying low over the ground and foliage, hunting for foraging and nesting potential victims.

There is also a family of cuckoo wasps which lay their eggs in the nests of potter and mud dauber wasps; many types of wasps in various families have evolved similar habits. These insects are normally referred to as "kleptoparasites," rather than "brood parasites." The distinction is that the term "brood parasite" is generally restricted to cases where the immature parasite is fed directly by the adult of the host, and raised as the host's offspring (as is common in cuckoo birds). Such cases are virtually unknown in bees and wasps, which tend to provide all of the food for the larva before the egg is laid; in only a few exceptional cases (such as parasitic bumblebees) will a bee or wasp female actively feed a larva that is not her own species. The difference is only in the nature of the interaction by which the transfer of resources occurs (tricking a host into handing over food rather than stealing it by force or stealth), which is why brood parasitism is considered a special form of kleptoparasitism.

The number of times kleptoparasitic behavior has independently evolved within the bees is remarkable; C. D. Michener (2000) lists 16 lineages in which parasitism of social species has evolved (mostly in the family Apidae), and 31 lineages parasitizing solitary hosts (mostly in Apidae, Megachilidae, and Halictidae), collectively representing several thousand species, and therefore a very large proportion of overall bee diversity. There are no cuckoo bees in the families Andrenidae, Melittidae, or Stenotritidae, and possibly the Colletidae (there are only unconfirmed suspicions that one group of Hawaiian hylaeine species may be parasitic).-- from Wikipedia

"Kleptoparasitism is an important means by which many animals obtain limited resources. The success of kleptoparasitism may be influenced by a number of factors, including competitive differences among individuals and the spatial distribution of prey and hosts." --Read the Abstract: Ian M. Hamilton, Behavioral Ecology Vol. 13 No. 2: 260-267, © 2002 International Society for Behavioral Ecology, Kleptoparasitism and the distribution of unequal competitors