There are about 150 species of mason bees in North America. They tend to be metallic green, blue-black, or blue-green in color and have beefy little bodies. Most species are active in early to late spring. Depending on the species, they either excavate a nest in the soil or use hollow stems (or bee hotels put out by bee lovers). This particular species constructs in existing holes (approximately 6 mm in diameter), often in wood but sometimes in other locations such as hoses, bamboo, or abandoned pipes. Eggs are laid in individual cells that are made of clay / mud or other materials.
Photo by Kristi Dubois on 4/24/20 in Missoula, MT.