The term sweat bee refers to bees in the family Halictidae. Some members of the Halictidae family are attracted to the salt found in human sweat, this is how they got their common name. Fortunately this bee, which I photographed at the Maplewood Nature Center back in August, was much more interested in the flower.
There are about 1000 types of sweat bees living in North and South America. Most of them are small to medium size, which may be why they seem to be relatively inconspicuous even though they are typically the most numerous type of bee, and are black, brown, red or metallic green in color.
Metallic green sweat bees are a member of the genus Agapostemon. There are over 45 species of these green bees in North America. Unlike honey bees and bumble bees most of the green bees are solitary nesters, nesting in borrows that they dig under ground. Even in species of green bees that do nest communally usually each female typically builds her own nest cell. Since most green bees are not very aggressive and do not sting very hard they are usually not considered pest species. In fact, since they tend to be floral generalists, they visit a wide variety of flowers, they are usually considered a beneficial species. They collect pollen, which they bring back to their nest, by use of a series of brush like hairs, called scopa, on their hind legs.