Cuckoo bee

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Cuckoo bees are bees that lay their eggs in the nests of other bees, stealing the host’s food and brood space much like cuckoo birds do with other birds.

Most often, the term refers to the subfamily Nomadinae, but in Europe it’s sometimes used for certain bumblebees in the Psithyrus group.

Female cuckoo bees are usually easy to recognize: they don’t collect pollen and they don’t build their own nests. They often have less body hair and a tougher-looking, sometimes sculptured body with strong jaws, though this isn’t universal.

Many different bee lineages have evolved kleptoparasitism. Research has counted about 16 lineages that parasitize social bees and about 31 lineages that parasitize solitary bees, spanning thousands of species and a large part of bee diversity. Cuckoo bees are not found in the families Andrenidae, Melittidae, or Stenotritidae, and possibly not in Colletidae; Hawaii’s Hylaeus may have one uncertain example.

Cuckoo bees usually invade nests of pollen-collecting species and lay their eggs in the host’s brood cells. When the cuckoo bee larva hatches, it eats the host’s pollen ball and often kills the host larva if the host larva isn’t already dead.

In cases where the host is a social bee (such as some Bombus, the bumblebees), the kleptoparasite may stay in the nest and lay many eggs, sometimes killing the host queen and taking over the nest. Such bees are often called social parasites, though some are also brood parasites.

Many cuckoo bees look similar to their hosts, which fits the idea that close relationships shape their appearance. This idea is known as Emery’s Rule.

There are also cross-family examples. For instance, Townsendiella, a nomadine bee, has one species that parasitizes a melittid bee (Hesperapis) while other Townsendiella species attack halictid bees.