California Mason Bee

Osmia californica · Order: Hymenoptera · Family: Megachilidae

No source yet on danger. We have no source yet on whether it bites, stings or damages anything.
California Mason Bee
Photo: USGS Bee Inventory and Monitoring Lab from Beltsville, Maryland, USA, Public domain

The California mason bee is a solitary mason bee that builds nests with leaf pulp partitions. It is native to North America and emerges a bit later in spring than the orchard mason bee. These bees are important pollinators, visiting over 33 genera across 13 plant families.

Source: Wikipedia

How to recognize it

California mason bee belongs to the megachilid family of mason bees.

Source: Wikipedia

Where it lives

It nests alone, constructing nests with leaf pulp that creates a protective partition for the egg chamber.

Source: Wikipedia

What it eats

The species pollinates more than 33 genera from 13 different plant families.

Source: Wikipedia

Life cycle

Adults emerge a little later in spring than the orchard mason bee.

Source: Wikipedia

When you see it

Their emergence occurs later in spring compared with the orchard mason bee.

Source: Wikipedia

Where it comes from

It is native to North America.

Source: Wikipedia

Lookalikes

Like the orchard mason bee, it is a solitary nester that uses leaf pulp partitions in its nest.

Source: Wikipedia

Where it is found in the US

Recorded in 12 of 51 states and DC. Most records: California, Utah, Washington, Arizona, Wyoming, Oregon, Nevada, Idaho.

Darker = more records. Counts are museum and citizen-science records, not population size.

Source: GBIF

Status: native in North America; native in United States; native in Canada. Source: iNaturalist

Months it is reported in the US

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Source: GBIF

More photos

California Mason Bee photo 3
Photo: USGS Bee Inventory and Monitoring Lab from Beltsville, Maryland, USA, Public domain
California Mason Bee photo 4
Photo: Yellowstone National Park, Public domain
California Mason Bee photo 5
Photo: USGS Bee Inventory and Monitoring Lab from Beltsville, Maryland, USA, Public domain
California Mason Bee photo 6
Photo: USGS Bee Inventory and Monitoring Lab from Beltsville, Maryland, USA, Public domain

Questions people ask

When do California mason bees appear?

They usually emerge a little later in spring than the orchard mason bee.

Source: Wikipedia

What plants do they pollinate?

They pollinate over 33 genera across 13 plant families.

Source: Wikipedia

Where are they native to?

They are native to North America.

Source: Wikipedia

How do they build their nests?

They construct solitary nests using leaf pulp to create a partition that protects the egg chamber.

Source: Wikipedia

Same family (Megachilidae)

European Woolcarder BeeEuropean Woolcarder BeeAnthidium manicatumRed Mason BeeRed Mason BeeOsmia bicornisCan stingEuropean Orchard BeeEuropean Orchard BeeOsmia cornutaSculptured Resin BeeSculptured Resin BeeMegachile sculpturalisOblong Woolcarder BeeOblong Woolcarder BeeAnthidium oblongatumFlat-tailed Leafcutter BeeFlat-tailed Leafcutter BeeMegachile mendica

Sources

  • Wikipedia: https://en.wikipedia.org/wiki/Osmia_californica

Look it up elsewhere: GBIF · iNaturalist · BugGuide · ITIS · Wikipedia

Text written 2026-10-23 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-23.

How this page works

This is one bug's fact sheet. The colored box at the top says whether it is dangerous. Sections below cover how to recognize it, whether it is a pest, and how to deal with it. The US map shows which states have records; tap a state to see other bugs there.

Every fact on Bug FAQ comes from a named source (university extension sites, government agencies, GBIF, iNaturalist, Wikipedia). The source is linked next to each section. If we have no source for something, we leave it out.