Genus: Osmia Panzer, 1806
Subgenera: Allosmia, Cephalosmia, Diceratosmia, Erythrosmia, Euthosmia, Helicosmia, Hemiosmia, Hoplosmia, Melanosmia, Metallinella, Mystacosmia, Nasutosmia, Neosmia, Osmia, Pyrosmia, Tergosmia, Trichinosmia
Common name: mason bees
Bees in the genus Osmia are commonly referred to as “mason bees,” due to their habit of using mud, pebbles, or chewed leaf material to build nest compartments. Osmia means “odor,” which refers to the lemony scent the bees produce when marking their nest entrances (Wilson and Carril 2016). This secreted odor allows them to distinguish their nest entrance from other Osmia nesting entrances found nearby (Wilson and Carril 2016). They generally have a short, robust body form and range in body length from 7–13 mm (Michener 2007). Coloration ranges from metallic green to blue to black (Michener 2007).
(modified from Michener 2007)
Osmia may be confused with Stelis and Hoplitis due to similar shape and coloration, but can usually be differentiated by the elongate parapsidal line in Hoplitis and the lack of scopal hairs in the females of Stelis (Michener 2007).
Osmia caerulescens is native to Europe and North Africa and was accidentally introduced to the U.S. sometime in the 1800s. It has been collected in the northeastern and north-central half of the U.S., but it is not as common as it once was (Sheffield et al. 2011).
Osmia cornifrons is native to Japan but was intentionally introduced to the U.S. in the 1960s to pollinate orchards and is still used commercially (Bosch et al. 2008). It has since been used to pollinate blueberries, melons, strawberries, legumes, and mustard crops. There are now naturalized populations in the Mid-Atlantic and northeastern U.S. (Bosch et al. 2008). A few specimens have been collected in Oregon, but populations do not appear to have become established.
Osmia cornuta is native to Europe and North Africa and was intentionally introduced to the U.S. in the 1980s to pollinate crops (Torchio and Asensio 1985). Established wild populations of this species have not been documented.
Osmia taurus is native to Asia and was accidentally introduced to the U.S. as early as 2000 and is now common along the eastern part of the country (Russo 2016). It looks very similar to O. cornifrons, and they are easily mistaken. This could be why O. taurus was introduced to the U.S. (Giles and Ascher 2006).
Many Osmia are generalists and will collect pollen from a range of flowering plants. Flowers that are favored by Osmia are often tube-shaped or asymmetrical, such as plants in the family Fabaceae (Wilson and Carril 2016).
Osmia nest in pre-existing cavities, such as snail shells, abandoned nests, rock fissures, dead wood, and hollow stems, using mud, pebbles, or chewed leaf material to build nest compartments (Michener 2007; Gonzalez et al. 2012). They do not form colonies or hives, but may nest in close proximity to one another.
Osmia are widely abundant throughout Europe, the Mediterranean Basin, southwestern Asia, and western North America (Michener 2007). Over 130 species are found in the United States and Canada (Wilson and Carril 2016). Fewer than 30 species occur east of the Mississippi River (Michener 2007; Wilson and Carril 2016). Osmia thrive at a wide range of elevations, from sea level to high above the tree line, and are common in regions with temperatures that drop below 0° C.