Cliff Mason Bee

The Cliff Mason Bee, Osmia species, is one of numerous solitary bees in the large genus Osmia, family Megachilidae, whose females construct individual brood cells from mud, clay, or resin in crevices on cliff faces, rock walls, and outcrops. Mason bees are important pollinators of wildflowers and orchard crops, collecting pollen and nectar to provision their nests. Cliff mason bees take advantage of natural crevices in rock faces as nesting sites, plastering cells of mud mixed with sand grains or plant material to subdivide the crevice into individual egg chambers. Each cell contains a pollen-nectar mass food provision and a single egg before being sealed with a mud plug. Males typically emerge first in spring, followed by females, and adults live for only several weeks, devoted entirely to mating and nesting. Cliff-nesting Osmia species are found in rocky habitats across the Holarctic region, from Europe through Asia and North America. The availability of suitable nesting sites on cliff faces, combined with the proximity of diverse wildflower resources, determines population density. Many solitary bee populations have declined in recent decades due to loss of nesting habitat and floral resources. Specific conservation status depends on the species intended.