Halictidae is the second-largest family of bees (clade Anthophila) with nearly 4,500 species. They are commonly called sweat bees (especially the smaller species), as they are often attracted to perspiration. Halictid species are an extremely diverse group that can vary greatly in appearance. These bees occur all over the world and are found on every continent except Antarctica. Usually dark-colored (frequently brown or black) and often metallic, halictids are found in various sizes, colors and patterns. Several species are all or partly green and a few are red, purple, or blue. 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 one of many with short tongues and is best distinguished by the arcuate (strongly curved) basal vein found on the wing. Females in this family tend to be larger than the males. They are the group for which the term eusocial was coined by entomologist Suzanne Batra.
Ecology
Most halictids nest in the ground, often in habitats like clay soil and river banks, though a few nest in wood. They mass-provision their young; a mass of pollen and nectar is formed inside a waterproof cell, an egg laid upon it, and the cell sealed off, so the larva is given all of its food at one time, as opposed to "progressive provisioning", where a larva is fed repeatedly as it grows, as in honey bees. Some species line their tunnels with lactone secretions to help workers return to the nest. It is thought that each individual bee has its own unique chemical signature. All species (except for kleptoparasites) are pollen feeders and may be important pollinators.
Systropha planidens, a specialist pollinator of Convolvulus
Many species in the Halictidae are eusocial at least in part, such as Lasioglossum malachurum, with fairly well-defined queen and worker castes (though not the same as the caste system in honey bees), and certain manifestations of...
