Osmia

Osmia is a genus of bees in the family Megachilidae, commonly known as mason bees. The genus contains about 350 described species found in temperate regions worldwide. Osmia bees are primarily solitary cavity nesters, unlike social honeybees or bumblebees, and they are important pollinators of fruit crops and wildflowers.

Female Osmia carry pollen on specialized hairs under the abdomen (the scopa) rather than on the hind legs. Body size and color vary by species, with some displaying metallic blue or green hues in addition to darker forms. Notable species include Osmia lignaria, the blue orchard bee, and Osmia bicornis, the red mason bee, both valued for pollination in orchards and gardens.

Nesting biology centers on preexisting cavities such as hollow stems, holes in wood, or artificial nesting blocks. Each brood cell is constructed or partitioned using coarse mud or chewed plant fibers and is provisioned with a mixture of nectar and pollen before an egg is laid. The cell is then sealed. Larvae develop within the cell, pupate, and typically overwinter as adults or prepupae, depending on species and climate. Most Osmia species are unicolonial and solitary, though groups may nest near one another.

Ecology and pollination: Osmia bees are efficient pollinators of fruit trees (such as apples and almonds) and early-blooming flowers. They can operate at cooler temperatures than some other pollinators and are often used in managed pollination programs. Their foraging preferences contribute to the reproduction of a wide range of plant species.

Conservation and management: Habitat loss and a shortage of nesting sites, along with pesticide exposure, threaten Osmia populations. Conservation measures include preserving dead wood and hollow stems, providing artificial nesting sites and access to mud or clay, and maintaining pesticide-free foraging habitats.