Mason bees
Osmia spp.
Bee
Genus-level entry for the solitary mason bees, named for the mud or clay partitions females use to wall off the cells of their nests. Roughly 140 Osmia species occur in North America, including the native blue orchard bee (Osmia lignaria) and the blueberry bee (Osmia ribifloris). They are cavity nesters that do not excavate their own holes - instead occupying beetle burrows, hollow stems, and gaps in wood, and readily adopting drilled blocks and reed or paper tubes. Active in early spring, mason bees are highly efficient pollinators of Rosaceae fruit trees (apple, pear, cherry, plum, almond, peach) because they carry dry pollen on the underside of the abdomen and forage in cool, overcast weather when honeybees stay in the hive.
Conservation
No genus-wide IUCN listing; the native blue orchard bee (Osmia lignaria) is widespread and not considered at risk. However, several native Osmia species have declined since around 2020, a trend linked to competition and pathogen spillover from introduced congeners such as the hornfaced bee (Osmia cornifrons). Supporting native mason bees means prioritizing native species, providing clean undyed nesting tubes that are replaced or sanitized between seasons, and avoiding the spread of imported bees and their parasites.
Plan for this species
Location-fit plant set for Chicago, IL: host and specialist plants first, then nectar, fruit, seed, foliage, and shelter plants that still fit the current and mid-century climate read.
0 essential relationships / 6 supporting plants
Host/specialist links: 0
Forage/pollination links: 6
Shelter links: 0
Relationship roles: 1
American plum
Supporting / Plants this species pollinates
Apple
Supporting / Plants this species pollinates
Canadian serviceberry
Supporting / Plants this species pollinates
European pear
Supporting / Plants this species pollinates
Highbush blueberry
Supporting / Plants this species pollinates
Sweet cherry
Supporting / Plants this species pollinates
Plants in the catalog
Plants this species pollinates · 13
Spring-flying mason bees are effective early-season pollinators of orchard cherries.
Nectar plants · 7
Solitary bees such as mason bees visit the spurred flowers for nectar and pollen alongside honey bees and the long-tongued bumblebees that are best suited to reaching the nectar at the base of the long spurs.
Solitary mason bees visit the small open flowers for nectar and pollen across the sunny, well-drained sites this herb favours.
Mason bees and other solitary bees forage nectar and pollen on the flowers, drawn by the early, abundant, accessible bloom on a warm, sheltered site.
Mason bees are among the spring-to-summer solitary bees that take nectar from the woolly-bracted spikes; a plausible generalist visit on a good dry-ground bee herb.
Mason bees and other solitary bees forage the open, blue flowers for nectar; the dense summer spikes are a steady generalist nectar source.
Spring-active mason bees forage the early flowers for nectar where their season overlaps the start of bloom; graded plausible as generalist foraging on a Mediterranean nectar shrub rather than a documented specialist tie.
Early-emerging mason bees visit the late-winter to spring bloom for nectar.
Pollen plants · 4
Spring-active solitary mason bees readily visit the open, accessible flowers for pollen during their flight season.
Solitary mason bees also collect pollen from the readily accessible open flowers.
Spring-active solitary mason bees work the open, cup-shaped early flowers for pollen as they provision their nests.
Early-active spring solitary bees such as mason bees work the accessible white blooms for pollen during the late-spring flowering window.
Range
Native across temperate North America, with about 140 species; richest in regions where flowering Rosaceae trees and shrubs bloom in early spring. Two commonly managed species are non-native: the hornfaced bee (Osmia cornifrons) from eastern Asia and the red mason bee (Osmia bicornis) from Europe.
Sources & citations
Cite this page
Use this citation for the Plotwright wildlife record. Use the source cards below to explore the references that informed its taxonomy, range, conservation, host plants, foraging, and habitat.
Plotwright. (n.d.). Mason bees (Osmia spp.). Retrieved 2026, August 20, from https://plotwright.com/wildlife/mason-bees
Sources used for this record
This record is compiled from the sources below.
Wikipedia: Mason bee
Genus-level reference for Osmia taxonomy, cavity nesting, mud partitions, early-season orchard pollination, and native/non-native managed species context.
Scientific Reports: Decline of native mason bees after exotic congener arrival
Research source backing the caution that some native Osmia species declined after introduced managed congeners arrived.
GBIF: Osmia
GBIF backbone genus Osmia (Megachilidae) resolved to usageKey 1337664 after filtering multiple equal-name matches to the bee family.
iNaturalist: Osmia
iNaturalist genus Osmia (mason bees) with observation-backed distribution data.