The Mason Bee depicted at this page is much smaller than the Blue and Red Mason Bees are. We have had it in our garden regularly in 2002, but only when the plant you see it in flowers. We have never seen it make a nest in our garden, so probably it's only here to feed. Thanks to Jeroen de Rond we now know that this most probably is Osmia niveata. The smaller Osmia species are very hard to tell apart, though.