Nomada

Genus of bees

With over 850 species, the genus Nomada is one of the largest genera in the family Apidae, and the largest genus of cuckoo bees. Cuckoo bees are so named because they enter the nests of a host and lay eggs there, stealing resources that the host has already collected. The name "Nomada" is derived from the Greek word nomas (νομάς), meaning "roaming" or "wandering." Nomada are kleptoparasites of many different types of bees as hosts, primarily the genus Andrena, but also Agapostemon, Melitta, Eucera and Exomalopsis. As parasites, they lack a pollen carrying scopa, and are mostly hairless, as they do not collect pollen to feed their offspring. Like non parasitic bees, adults are known to visit flowers and feed on nectar.

They are often extraordinarily wasp like in appearance, with red, black, and yellow colors prevailing, and with smoky (infuscated) wings or wing tips. They vary greatly in appearance between species, and can be stripeless, or have yellow or white integumental markings on their abdomen. There are specialized patches of hair on the tip of the abdomen of female Nomada. Males have an obvious, often notched pygidial plate. Separation of this genus from other Nomadinae can be difficult; details of the wing venation, and the nature of the patch of silvery setae at the tip of the female metasoma are the best distinguishing features. Species of Nomada exhibit an unusual behavior where adult bees are observed to be sleeping by using only their mandibles to hold onto plants. All known species parasitize ground nesting bees, and their habitats and seasonality correlate with their hosts. Ground nesting bees nest in soil, either in open habitats or in ones covered with vegetation, with a good floral source nearby.

Bees of the genus Nomada most often parasitize bees of the genus Andrena, but have also been observed parasitizing other ground nesting bees in the families Andrenidae, Melittidae, Halictidae, and Apidae. As is the case for other nomadines, this behavior violates “Emery’s rule” which states that social parasites tend to be either closely related to or sister species of their host. Nomada are guided by visual cues to locate host nest entrances. In early spring, they can be spotted flying low to the ground, searching for nests to parasitize. Nomada parasitizes their host cells by laying eggs in host nests while the female host bee is foraging for pollen, or nectar. The female Nomada oviposits in the host's cells before host oviposition and nest cell closure. Other reports of Nomada mating includes males “swarming” willow and gooseberry plants. There is evidence that most species of Nomada are species specific to their hosts, and that males mimic the specific scents of the species they parasitize. However, not much research has been done to understand the specialization of Nomada, and it is known that some species are more generalist than others. See list of Nomada species for a complete list.