Blue Orchard Bee

The blue orchard bee is a solitary mason bee in the family Megachilidae, native to North America and closely related to other Osmia mason bees found across the Northern Hemisphere. It is prized in agriculture as a highly efficient pollinator of early-blooming fruit trees such as almonds, cherries, apples, and pears, often outperforming honey bees on a per-visit basis for these crops.

It is notable for its striking metallic blue-black coloration, its gentle temperament, and its use of pre-existing narrow cavities such as hollow plant stems, reed bundles, or drilled wood blocks for nesting rather than excavating burrows or building wax comb, which has made it easy to manage in simple artificial nesting tubes for orchard pollination programs.

Ecologically, it plays an important role as a spring pollinator active during a narrow window when many fruit trees bloom, and its solitary lifestyle means each female works independently to provision her own offspring rather than dividing labor within a colony.

• Small to medium bee, 8–13 mm long, with a compact, rounded body and a metallic blue-black to dark green sheen visible in good light.
• Moderately hairy, with pollen carried on a dense brush of hair (scopa) on the underside of the abdomen rather than the hind legs, typical of mason bees.
• Lacks the yellow-and-black banding of honey bees or wasps, appearing instead uniformly dark with an iridescent shine.
• Distinguished from other metallic bees by its stout, bullet-shaped body and characteristic use of hollow-stem or tube nesting sites.

Native to temperate North America, the blue orchard bee is found in woodlands, orchards, and gardens where suitable nesting cavities and early-spring flowering plants occur. It nests in narrow, pre-existing tunnels such as hollow reeds, beetle borings in dead wood, or man-made nesting tubes, and is active for a brief period in early spring, closely timed to coincide with fruit tree bloom.

Females forage individually for pollen and nectar, provisioning a series of linear cells within a tunnel, each separated by a mud partition (giving mason bees their name). They are efficient, fast pollinators, visiting large numbers of flowers per day and readily transferring pollen due to their dense body hair. Blue orchard bees are non-aggressive and rarely sting, tolerating close human activity in orchard settings where they are sometimes intentionally introduced via nesting boxes to boost fruit set.

This species undergoes complete metamorphosis with a single generation per year. Adults emerge in early spring, mate, and females provision a series of mud-walled cells in a tunnel with pollen and nectar before laying an egg in each and sealing the nest. Larvae hatch, consume their provisions, and develop through the summer into pupae, then transform into adults that remain dormant inside their cocoons through fall and winter, emerging the following spring to begin the cycle again.