The following material taken with permission from: Mitchell, T.B. 1962. Bees of the Eastern United States, Volume II. North Carolina Agricultural Experiment Station. Tech. Bul. No.152, 557 p.
This genus is a group of metallic green, blue or blue-green bees, with a short, robust body form. The basal abdominal tergum is flattened anteriorly but hardly concave, sometimes with a vague median sulcus. The metanotum and posterior face of the propodeum are perpendicular, forming the posterior surface of the thorax, and the scutellum is rounded, with rather large axillae. The notaulices are punctiform. and obscure. In the front wings both recurrent veins are received well within the limits of the 2nd submarginal cell. Arolia are evident between the claws, and the maxillary palpi are 5-segmented. Usually the abdominal terga are not fasciate. In the males tergum 6 usually has a small median apical emargination, and 7 is more deeply emarginate but is largely covered by 6. Sterna 1, 2 and 4 are exposed, but 3 is commonly hidden beneath sternum 2, while 5-8 are retracted and variously modified. There is a considerable diversity of nesting habits in Osmia, some of them excavating burrows in the soil, others using plant stems, vacated burrows of other bees, and empty snail shells. Sometimes these are lined with a paste made from plant tissue, and partitions between cells, or plugs closing the ends of the burrows, may be of this same material.