Osmia (Osmia) lignaria are dark metallic blue bees. They have a pale blue face that is covered with a mixture of white and black hair. The thorax has intermixed pale and black hair on the scutum and primarily black hair on the episternum. T1 and sometimes T2 are covered in white hair, and the remaining terga are covered with primarily black hair (Fig 6). Female body length is 7–13 mm, and male body length is 9–11 mm (Sandhouse 1939; Rust 1974).
Osmia lignaria be distinguished from other Osmia (Osmia) by its distinct blue-green hue in combination with the distinctly projected malar space in females and the subtriangular projection on the middle femur in males (Rust 1974). There are, however, two subspecies in the U.S., O. lignaria lignaria and O. lignaria propinqua, which can be more difficult to tell apart. Female O. lignaria lignaria can be distinguished from O. lignaria propinqua by their tridentate mandibles and the short lateral horns on their clypeus (Rust 1974). Males do not have reliable characters to distinguish between the subspecies (Rust 1974).
Osmia lignaria are polylectic (Torchio 1976). Osmia lignaria are used to pollinate apple, plum, cherry, and almond trees (Torchio 1976; Bosch et al. 2000; Bosch et al. 2006). They have also been observed visiting currant, dandelion, white clover, hawthorn, and rose (Torchio 1976; Phillips and Klostermeyer 1978).
Osmia lignaria often nests in abandoned burrows and hollow stems (Guisse and Miller 2011) . O. lignaria will also nest in man-made nesting materials, such as hollow nesting tubes or drilled wood blocks, allowing them to be collected and transferred to commercial orchard environments (Torchio 1976; Torchio and Asensio 1985). Each nest cavity contains multiple cells separated by mud partitions (Guisse and Miller 2011).
Osmia lignaria is native to North America and split into two subspecies: O. lignaria propinqua which is found west of the 100th meridian, and O. lignaria lignaria which is found east of the 100th meridian (Guisse and Miller 2011). All populations occur between sea level and 2000 m (Guisse and Miller 2011). O. lignaria are known to occur from the northern edge of Mexico to the southern half of Canada (Rust 1974). O. lignaria have also been documented in orchard fields in Spain, but it is unknown if they have become established (Ortiz-Sanchez 2011).