Mason bees are solitary native bees in the genus Osmia, with numerous species found throughout Arizona. They are named for their habit of using mud, clay, or other materials to partition and seal their nest cells — much like a mason uses mortar. Mason bees are among the earliest-emerging native bees in spring and are extraordinarily efficient pollinators; a single mason bee can pollinate as many flowers as 100 honey bees due to their less-precise pollen-carrying behavior (pollen falls off more readily, contacting more flowers). They nest in pre-existing small cavities — hollow stems, beetle borings in wood, gaps in mortar, and artificial bee tubes. The Blue Orchard Bee (Osmia lignaria) is commercially reared for orchard pollination across the western United States. Mason bees are completely non-aggressive; females will only sting if physically trapped or squeezed. They are a cornerstone of native pollinator conservation efforts in Arizona.