• Family: Megachilidae
• Approximate # species in region: 24
• Common name: mason bees

Osmia is a widespread genus of megachilids, mainly active in spring and early summer. Most are small to medium-sized, pill-shaped, and dark metallic green or blue. Nests occur both above and below ground, including in abandoned bee nests and beneath stones. Although some species are true masons and use mud to line their nests, others employ leaf discs, leaf pulp, wood shavings, resin, or stem pith. Of the nearly 20 species in eastern US, only a handful are currently known to be field identifiable. One of them, the blue orchard bee Osmia lignaria is managed commercially as a crop pollinator of fruit and nut trees.

Recognize Osmia by their big heads, round abdomens, abdominal scopal hairs, and often shiny integument. Megachile have similarly large heads and powerful jaws for gathering leaves, resins, and mud, but most have abdomens that are more elongate or more pointed than Osmia. Unlike Osmia, Megachile never have metallic integument. Also know that Osmia are mostly early-season bees that are not very likely to be encountered in our region after about mid-July (unlike Megachile, which don’t typically appear until May and are active throughout the summer and into fall). Hoplitis is another similar genus that flies at about the same time as many Osmia. All Hoplitis in our region have black integument and some degree of hair banding on their abdomen – our few nonmetallic Osmia have bumblebee-like hair patterns, without distinct banding on the abdomen.

Regional Species List: