Mason bees

Definition

Solitary bees in the genus Osmia (family Megachilidae) that construct nest partitions and plug entrance holes using mud, clay, or other masonry-like materials. Unlike honey bees or bumblebees, mason bees do not form colonies; females individually provision pre-existing cavities—such as hollow stems, beetle borings in wood, or rock crevices—with pollen-nectar masses and lay eggs separated by mud walls. Several species are managed as orchard pollinators, particularly for early-blooming tree fruits.

Etymology

From the use of mud or 'masonry' in nest construction.

Example

Osmia lignaria, the blue orchard bee, seals each brood cell with a mud partition and finally plugs the nest entrance with a hardened mud cap, earning the common name 'mason bee.'

Synonyms

• mud bees

Related Terms

• Osmia
• Megachilidae
• solitary bees
• cavity-nesting bees
• leaf-cutter bees
• nest provisioning
• orchard pollination

Usage Notes

The term is sometimes applied more broadly to other cavity-nesting bees that use mud, including some Hoplitis and Anthophora species, but specialists reserve it primarily for Osmia. Mason bees are often contrasted with 'carpenter bees' (which excavate wood) and 'leaf-cutter bees' (which use leaf pieces for nest lining). In conservation and agriculture contexts, 'mason bee' frequently implies managed populations in artificial nest blocks with removable paper straws or drilled wooden tunnels.