Nomada

With over 850 species, the genus Nomada is one of the largest genera in the family Apidae, and the largest genus of kleptoparasitic 'cuckoo bees.' Kleptoparasitic 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 parasitize 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. Given the lack of scopa and general behavior, they are considered poor pollinators. Most kleptoparasitic bees are believed to be solitary, but some may be primitively eusocial. Kleptoparasitic bees have independently evolved more than 16 times where they target social hosts, and over 31 times where they target solitary hosts. 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. In general, females are easily identifiable by the lack of scopa, reduced body hair, thick exoskeleton, and mandibles. 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. They occur worldwide, including Holartic, Central and South America, sub-Saharan Africa, and parts of Asia. A more detailed map of Nomada sightings can be found in this citation. Nomada parasitize ground-nesting bees, and therefore, their habitats 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. Species of Nomada have also been observed parasitizing 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.