All bees "hibernate" in the winter. Most bees hibernate as a larva or pupa, before they actually emerge as flying adult bees in the spring or summer.
Mason bees are solitary, and females will make their nests inside many different types of cavities, like those pictured below. The nest plugs (green, reddish, or leaf cutouts) were made by the female solitary bee to seal the nest. Inside, the bees sleep, and wait...
