What causes the small mounds of earth often described as looking like tiny volcanoes on a lawn?

Answer

The fine soil or ash displaced when the female digs her burrow.

The visible mounds are composed of the fine soil or ash that the female bee excavates while digging her burrow entrance and subsequent underground nest cells.

What causes the small mounds of earth often described as looking like tiny volcanoes on a lawn?
insectbeemanagementPest Controlashy