Halictidae is the second-largest family of Apoideabees. Halictid species occur all over the world and are usually dark-colored and often metallic in appearance. Several species are all or partly green and a few are red; a number of them have yellow markings, especially the males, which commonly have yellow faces, a pattern widespread among the various families of bees. The family is distinguished by the arcuate basal vein found on the wing. They are commonly referred to as "sweat bees", as they are often attracted to perspiration. They are only likely to sting if disturbed; the sting is minor.
Ecology
Most halictids nest in the ground, though a few nest in wood, and they mass-provision their young. All species are pollen feeders and may be important pollinators. ''
Eusocial species
Many species in the subfamily Halictinae are eusocial at least in part, such as Lasioglossum malachurum or Halictus rubicundus, with fairly well-defined queen and worker castes, and certain manifestations of their social behavior appear to be facultative in various lineages. Those species who do not have a permanent, rigid, division of labor, such as Lasioglossum zephyrus, are considered primitively eusocial. Another example of a primitive eusocial bee species from this family is the Halictus ligatus species, for which aggression is one of the most influential behavioralattitudes for establishing hierarchy and social organization within the colony. Primitively eusocial species such as these provide insight into the early evolution of eusociality. Halictus sexcinctus, which exhibits social, communal, and eusocial organization, provides insight into the evolutionary reversal of eusociality. Phylogenetic data from this species suggests that a communal strategy serves as a transitional step between eusociality and a reversion back to solitary nesting.
Cleptoparasitic species
Several genera and species of halictids are kleptoparasites of other bees, and the behavior has evolved at least nine times independently within the family. The most well-known and common are species in the genus Sphecodes, which are somewhat wasp-like in appearance ; the female Sphecodes enters the cell with the provision mass, eats the hostegg, and lays an egg of her own in its place.
"Nocturnal" species
Halictidae is one of the four bee families that contain some crepuscular species; these halictids are active only at dusk or in the early evening, so are technically considered "vespertine", or sometimes truly nocturnal. These bees, as is typical in such cases, have greatly enlarged ocelli. The other families with some crepuscular species are the Andrenidae, Colletidae, and Apidae.
Species of economic importance
Some species are important in the pollination of crops. Among these are the alkali bee, Lasioglossum vierecki and Lasioglossum leucozonium.
Phylogeny
Halictidae belongs to the hymenopteran superfamily Apoidea, series Anthophila. The oldest fossil record of Halictidae dates back to Early Eocene with a number of species, such as Neocorynura electra and Augochlora leptoloba known from amber deposits. Currently, the family is divided into four subfamilies, many genera, and more than 2000 known species. Rophitinae appears to be the sister group to the remaining three subfamilies based on both morphology and molecular data.
