Bees in the genus Osmia are collectively called mason bees or orchard mason bees because they cap their nests with mud. Mason bees, along with leafcutter bees ( Megachile spp.), make up two main groups in the Megachilidae family. Mason bees are abundant throughout Europe, the Mediterranean basin, southwestern Asia, and western North America. They are also found in eastern North America and eastern Asia, but are less common; these bees are not found in the southern hemisphere.

Mason bees are typically metallic green or blue, but some species are blackish colored. Mason bees are easily recognized because, unlike most bees that carry pollen on their legs, they carry pollen on the underside of their abdomens. Generally mason bees are good pollinators of blooming fruit trees, such as apple (Malus domestica), apricot (Prunus armeniaca), peach (Prunus persica), plum (Prunus spp.), cherry (Prunus spp.), and pear (Pyrus spp.). They also pollinate strawberry (Fragaria spp.), raspberry (Rubus spp.), blackberry (Rubus spp.), cranberry (Vaccinium spp.), and blueberry (Vaccinium spp.).