Sweat bees are tiny bees of the family Halictidae. They take their common name from their affinity for human sweat, which they lap off of our naked skin for the salts and electrolytes therein. Sweat bees are small (at least to us) and tend to measure between 3 and 10 millimeters in length. A few species have thick robust bodies, but most are slender and delicate. They tend to be glossy black, but some have exoskeletons which are gorgeous shades of metallic gold, green, purple, or blue.
The majority of sweat bee species nest in the ground (although a few build their homes in dead trees). The social behavior of sweat bees runs the entire gamut of bee conduct: the University of Florida Department of Entomology Website states, “species can be solitary, communal, semi-social, or eusocial.” Sweat bees therefore greatly interest entomologists who are studying the development of eusocial insects—those hive-minded insects which form colonies made up of a mass-reproducing queen served by a number of biologically sterile individuals. Most species of sweat bees live together in a simple underground tunnel-hive where they act more like roommates than like city-states, however some halictids do indeed create caste-based societies (albeit not as large and elaborately organized as those of honey bees or ants).
Sweat bees mass-provision their larval offspring—which is to say they stick a mass of pollen inside a waterproof cell, place an egg on it, and seal then it off until a functional adult emerges (as opposed to honey bees which lovingly feed the larva as they develop).
Halictidae species are immensely important to flowering plants. They are critical pollinators for many wildflowers, crops, and fruits. Therefore, although the creatures usually fly beneath our notice, they have a tremendous importance to humankind and to ecosystems as a whole. Not all sweat bees are virtuous workers: some species are cleptoparasitic and lay their eggs on the pollen masses accumulated by another species of bee. A handful of these little bees are outright parasites in the manner of the parasitoid wasps.
Like their fiercer large relatives, sweat bees are capable of stinging, however their stings are weak (which is fortunate considering their affinity for landing on us). Sweat bee stings rate a lowly 1.0 on the Schmidt Sting Pain Index (a remarkably poetic scale for rating the discomfort caused by hymenopteran venom). I have been stung by a sweat bee and the sensation was that of a needle-like itch which penetrated deep below the skin and then subsided almost immediately.
The sweat bees are cosmopolitan, which means they can be found throughout all similar habitats in the world (although they are thin on the ground in Australia and South East Asia). However the sweat bees are cosmopolitan in another way: alert reader, Michael Donohue (who is always on the look-out to identify his fellow native New Yorkers), sent me an article which details the discovery and naming of a new species of Halictidae, Lasioglossum gotham, which Dr. John Ascher, a bee researcher at the American Museum of Natural History, discovered in Brooklyn Botanic garden in 2009. In the NY Times article about the discovery, Ascher describes how New York City has a very rich diversity of wild bees.