I noticed the red mason bees mating (again) on the wall at the front of our house earlier in the year. This is a link to the red mason bees mating last year http://urbanwildlifejottings.blogspot.co.uk/2011/04/red-mason-bees-mating.html
The female makes a series of cells with soft soil and packs each cell with a paste made of pollen and nectar, which will feed and nourish the single larvae in each cell. The female does not have pollen baskets, but carries it on the underside of her body.
These are fascinating bees to watch and I would definately recommend anyone to have a go. At the same time you will also be helping bees. Red mason bees are particularly useful in that they pollinate fruit trees such as apple.
One day I watched two bees that behaved quite oddly. It was almost if they had forgotten which hole they were nesting in.
To date, nine of the nesting tubes have been used and pluged with mud. Two others still have bee vistors
My home made bee home around the front of the house is also being used by red mason bees.