2012 was the last year I used the mason bee colonies that were just holes bored in various experimental pieces of wood. I had attached these on the house, just behind a peach tree . They looked crude but were responsible for collecting from the wild my starter colony of mason bees. The main disadvantage however was that I could not clean these out, and parasites would take their toll each year. It is a good idea to get rid of these if you have used them so that you do not increase the parasites over the years.
UPDATE : We now call mason bee homes like this MASON BEE MORGUES