I wrote about European Orchard Bees Osmia cornuta in early April. Orchard Bees are a type of mason bee and they nest in holes in wood or masonry. All April the females have been inspecting our house for nesting potential. They don't make the holes themselves, rather they use existing holes if they are unoccupied and of a suitable depth and diameter.
One afternoon it looked like this, with a pollen layer visible...
Red Mason Bees are actually less red than European Orchard Bees, and emerge slightly later. Although native to Europe, they are also available commercially for people who want to improve the pollination of their fruit trees, and are therefore a much more widely known species.
a feature of mason bees.