Life Underfoot ~~ or ~~ The Pyramids of Beeza

Last Spring I was introduced to an aggregation of solitary bees nesting underground, in the lawn and landscape of an Olympia area home.  I was able to watch it regularly last year and this year have observed them a few times more.  The population remains robust as does my fascination for them.  While I have not actually counted, I suspect that there are tunnel entrances near a hundred.

I have learned a lot about these bees in the past year.  Tempting to describe this population a "colony", this inacurately suggests (at least according to bee experts) that there is organization and leadership.  So instead a massed population of solitary bees is called an aggregation -- a build-it-yourself housing complex minus the manager.  This aggregation that I'm watching starts where a concrete driveway and gravel parking bed borders a casual, mowed patch of lawn.  Along the gravel parking the (human) residents have placed lengths of round red timbers as a decorative border. Under the timbers the bees push and dig their way along the board and then continue excavating into the soil. Elsewhere are telltale soil mounds that surround each entry and these wonderful little pyramids, called tumuli, (singular: tumulus) extend several feet from the driveway edge into the lawn and garden beds.

It surprises me as to how many years I took for granted the many little mounds of dirt in garden edge and sidewalk crack, of life underground.  Admittedly they are mysterious and a bit frustrating.  Last year Janet and Nancy and I sat with these bees for an hour watching them, and Nancy and I each tried with only modest success to photograph them. These bees circle and circle several holes, forcing us into a guessing game of which hole to watch, and then "poof" the bee vanishes down one of them.  This year I tried again. Blurry as these photos may be, they are for now our best.

Look close - an ant "hitchhiker" on this one's back.
The bee did not fly until after the ant disembarked.

Identification of ground nesting bees begins with how the bee forms her individual nest cells and what physical adaptations she possesses for building underground. Some bees are easy to identify on the wing and in the flower.  Many are not.  Some are bigger than a honeybee, many more are very small.  Of the thousands of species of bees in the world, 70 percent are said to nest in the soil.   Seventy percent!!  That means that even in western Washington there likely are several dozen species of ground nesting bees. 

Bee approaching ground nest. Nancy Partlow 2013

The three main ground-nest building families (in North America) - Andrenidae, Halictidae, and Colletedae, are separated by very different UNDERGROUND habits.  Identification often requires a microscope, a shovel, or both. 

• Halictidae includes sweat bees, are usually very small and metallicly shiny.  Many are communal, sharing a common entrance and for a few there is even some shared provisioning and patroling, though usually every female is an egg layer. Some do not nest in the ground.

drawing from UC Riverside 2003 webpage
 adaped from from Stephen et al., 1969
UCR link no longer works.

• Colletidae bees are a "short-tongued" solitary bee and and also called polyester bees, because they coat each cell wall with an organic polyester that becomes a waterproof sack.  Using glandular secretions, she paints the cell with her very distinctive tongue.  She provisions into the sack a wet mix of pollen and nectar, lays one egg, and seals it up.  Often the food mass is soupy and the egg may be attached to the sack above the food. 

• Andrenidae bees are a "long tongued" ground nesting bee.  The female plasters a (different) glandular mix onto the cell wall with a special paddle part of her hind end; her mixture glues the soil together.  The food mass is typically more solid than Colletids.  Some andrenids are parasitic "cuckoo bees" that rely on others bees to build and provision nests that they then overtake.  There are many different species of Andrenidae bees; the subject of this blog is probably one. *

There are other groups of bees that also nest underground.  Bumblebees often nest in the ground, depending upon what they find that suits them, and have different habits.

When a year ago I started watching these bees I also started this post, then set it aside.  Perhaps it is a character flaw, but if I'm going to write about some creature and pretend that I know something, I want to be to able to identify it at least to family and hopefully to genus.  Here it is, a year later, and still I remain unable to put a name to this bee.  In this last year it did become a minor mission to learn more about mining bees.  The mission will continue.  And, while I still have not identified the subject of this post, I am at least more at peace with my public ignorance.

Glen

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* I have since learned from fellow bee friend Rusty that this is indeed an Andrenid bee. Getting this bee to Genus will have to do, is where our knowledge stops, is as far as her informant is willing to go.  If pressed, we might be able to narrow it down to one of a dozen or two possiblities, based on location, size, etc., but I am pleased that I can get this far -- and presently not driven to go farther.

Visit Rusty Burlew's page http://www.honeybeesuite.com/andrena-mining-bees/ for better photos and more detailed info as to why these are Andrena.
GB 5/23/14

Bugguide - Native Bees of North America

Photos Glen Buschmann unless otherwise credited.