Average size is approximately 3/4 of in inch. They are bright lime green with a black mark on top of the thorax. The eyes are reddish in color as are the legs.
After mating, females lay eggs near water and the larva live a fully aquatic life where they feed on algae. In order to breathe they will extend the tip of their abdomens thru the surface of the water to gain oxygen. Adults are often found nectaring at flowers or may be found gleaning nutrients from dung.
These flies are most likely bee mimics or perhaps wasp mimics. There is no question that their similarity to many metallic wasps and bees is uncanny.