Osmia (Osmia) ribifloris are bees with a metallic blue-green body. Females have black hair on the head, thorax, and abdomen (Sandhouse 1939). Males have intermixed black and white hair on their face, scutum, prim, and thorax. They have primarily white hair on T1 to T3 on and primarily dark hair on the remaining terga. Female body length is 10–12 mm, and male body length is 9–10 mm (Rust 1974). O. ribifloris is an important pollinator of blueberries in the U.S. (Torchio 1990).
Osmia ribifloris females can easily be distinguished by the combination of metallic blue to green integument, black hair throughout their body, and relatively simple clypeus that lacks lateral horns or a median emargination. Male O. ribifloris can look similar to O. pedicornis, but they can be differentiated by the shape of the gonocoxites, which are more expanded subapically in O. ribifloris.
Osmia ribifloris adults have been recorded in flight during all months except September and November (GBIF 2019g).
Osmia ribifloris specialize in pollinating manzanita (Ericaceae: Arctostaphylos) but are also commonly used to pollinate blueberries (Ericaceae) in commercial landscapes (Torchio 1990).
Osmia ribifloris nests in abandoned Sceliphron nests and in man-made structures, such as drilled holes in wood blocks (Rust 1986; Cane et al. 2007). Cells are arranged in a linear series throughout the nest. Cell partitions and nest plugs are comprised of masticated plant material (Rust 1986).
Osmia ribifloris is native to the western and southwestern U.S. (Rust 1974; Russo 2016) and is distributed from Oregon south to Mexico and east to Alabama (GBIF 2019g). Osmia ribifloris was intentionally introduced to Maine in 1991 (Stubbs et al. 1994); however, it is unknown if they have become established there (Russo 2016).