Solitary, small black hairless bees with a short, blunt tongue, bilobed at the tip. Limited yellow or cream markings usually present on the head, thorax and legs. No hairs for carrying pollen, which is carried with nectar in the crop. Aerial nesters usually in dead stems, or in crevices such as old beetle burrows and nail holes in wood. Cells are arranged in a linear series and waterproofed by a cellophane-like material. Each cell with one egg which is laid on a semi-liquid food store of pollen and nectar. One generation a year, usually over-wintering as a diapausing prepupa. Usually polylectic for pollen sources. Nationally: 12 species.