The Wasmann Journal of Biology  (Vol 32 no 1 1974) has an excellent article on a variety of bee species including Osmia californica.  It includes range maps of Osmia species. The known distribution of Osmia californica is in western North America and eastwards to Montana and Colorado (including British Columbia, Washington, Oregon, California, Idaho,Wyoming, Utah, Nevada) but not in Arizona or New Mexico. 
Female color is metallic blue black, legs black to reddish black.  The mandibles have 4 teeth.
Male is black to metallic blue black. 
The male and female varies from entirely black to black with white tufts and areas of intermixed black and white.
It appears as early as May in the southern and warmer location and as late as August in higher altitudes.

Biology:  The egg is located in the center of the pollen store, with the store usually filling the cell.  The cell and plug partitions are constructed of small pieces of masticated leaf and mud.  The amount of leaf varied from 1% to 50% of the partition.  The partitions were tough, with the outer surface shallowly concave and smooth.  The inner surface was rough and the spiral ring construction was easily seen.

2 Responses to Osmia californica – Richard W. Rust

  • Unknown says:

    Dr. M,
    I was helping a customer with figuring out how to clean her mason bee nesting systems &
    I found something I have never seen in all these years of opening the nesting systems.

    Some LARGER than normal cocoons (almost 2X bigger than female mason bee cocoons) were on top of the block totally surrounded in either cottonwood cotton or insulation??? Are these a type of bumble bee cocoon?
    Mystified Mary in Marysville!

  • healthfull says:

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