Osmia californica comes out late in spring, often their emergence overlaps the latter end of the Osmia lignaria (early spring mason bee) season.

However very little is known about them.  If you’d like to share your photos of Osmia californica, please email them to me and I will get them on this blog.

I had to go to my old stomping ground to get this article.  In 10 years Simon Fraser University did not seem to have changed much- although I did only go to the library.  It is a short ride from my home and so tonight I thought to chase up the 1966 article by Levin.  I wondered into the library, walked up to the 5th floor and found The Journal of Kansas Entomological Society.  Just like that!  I spent a lot of my time in amongst these rows and rows of journals.  So it was not surprising that I found the green volumes so quickly.  Unfortunately there was no volume number 39.  I went to information and a kind gentleman looked to see if the library had it hidden from my view.  No, but library did have it in digital format.  Perfect!  It was fairly simple to search for it on the computer and get it printed out.  Parking for 55mins was $3.25!  But enough about my adventure. 

Here is what Levin had to say about Osmia californica.  Levin compares Osmia lignaria with Osmia californica.  I will focus on the details of Osmia californica.

Osmia californica
-Restricts pollen collection from a few composites
-Does not always overwinter as an adult (lignaria overwinters as an adult)
-About half of 33 overwintering cocoons were prepupae and the remaining half were adult
-Uses a mixture of mud and small amount of leaf tissue (lignaria uses mud only)
-Leaves no vestibule at entrance to nest (lignaria leaves a vestibule)
-Seals last cell with a thicker partition and does not build an end plug
-Buries its egg within the pollen mass (lignaria lays the egg on top of the pollen mass).

I think the most interesting part of this information is that Osmia californica does not always complete their transformation into an adult bee by winter.  This means that some bees overwinter as prepupae and complete their development the following spring.

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.

Finding anything written about Osmia californica is not easy.  Although I found an article written on californica by M. D. Levin, his scientific article was published in the Journal of Kansas Entomological Society, 1966.  Unless you are affiliated with a university, only the abstract is available.  I will write a summary of the article when I get the full article.  But I did find a great web site with good and very detailed photos of Osmia californica.  Link to photos of Osmia californica