This small bee is called a sweat bee because it loves… sweat! The salt in perspiration attracts sweat bees. They live in all countries around the world but tend to prefer a temperate climate.
Halictidae is the second-biggest family of bees. There are close to 2,000 species of which about 1,000 species can be found in North and Central America. Most are brown and black and they can have yellow stripes or markings. Some of the most flamboyant bees of all are sweat bees with metallic neon shades of blue, red or green, like genus Agapostemon, and some have colorful bands of color. With so many species and colors, sweat bees can be hard to identify.
A distinguishing feature of this bee family is that they have a strongly curved basal vein on their wings. These solitary bees are not large, with adults usually in the range of 3-10 mm or up to 0.5 of an inch long. They have pollen baskets on their back legs, which they load up with pollen to carry back to the nest to feed their young.
Sweat bees are highly valued as pollinators. A few species are considered pollinators of economic importance, like alkali bees, lasioglossum vierecki bees, and lasioglossum leucozonium. The alkali bee is used by commercial alfalfa seed growers to pollinate their crops. They even go so far as to create salt-producing alkaline soils to keep these bees happy.
This 1:22-minute video by Nature in Motion shows a glorious green sweat bee as she forages:
These are generalists, happy to forage for nectar and pollen on any number of flowering plants. They seem to enjoy a wide range of flavors. Flowers prefer dedicated pollinators so they know their pollen will be paired up with their own species, but it is probably better for the survival of the bees that they have a wide range of tastes.
They make their nests underground and feed their colonies and themselves with pollen and nectar. Like carpenter bees, they provision a batch of pollen and nectar as food for their young, place the egg on top and seal off the cell.
Some species of halictids are kleptoparasitic, which means they enter another bee’s nest, usually another halictid, devour the egg and replace it with their own egg. Species in the genus Sphecodes are known for this behavior, and they can look like black wasps with blood-red abdomens.
Female sweat bees sting, and although the sting is minor if they are stopped quickly, they continue pumping venom into their victim until they are brushed away, so if one stings, remove it as soon as possible to minimize the damage. To avoid being stung, don’t get too close to their nests, don’t cast a dark shadow over their nest, and be aware that ground vibrations near their nests gets them agitated.
Halictidae is one of four families that contain bees that forage either at twilight (crepuscular species) or at night, being totally nocturnal. These bees have enlarged ocelli to see better in dim light or darkness.
If sweat bees are nesting in your garden and you do not want them, please do not spray pesticide. They are easy to get rid of by just planting some flowers or shrubs or cover the soil where the nest opening is with landscape fabric or mulch.