One of the most common bees in Eastern North America, particularly in urban and disturbed environments.
They are attracted to piles of dirt or open scraped soils and appear to be a huge fan of clovers, plants that also favor lawns and open disturbed sites. The female (look it up) mirrors most other small, dark bees in that group, with a few white marks on its lower face.
The male Calliopsis andreniformis pictured here is spectacularly different. Brilliant yellow to an exhibitionistic level. This one comes from Baltimore City.