Osmia is a genus of solitary bees commonly known as mason bees. They are known for their efficient pollination abilities and are often used as alternative pollinators in agriculture. Osmia bees are typically small to medium-sized, with a stout body and a metallic sheen. They construct their nests in pre-existing cavities, such as hollow plant stems or holes in wood, using mud or chewed plant material to create individual cells for their eggs.