Last spring a bee hotel that I built on the wall next to my back door went largely unused, but this year competition by Osmia rufa is keen. About 11 holes are already sealed with mud and more nests are being constructed as I type. I had wondered last year if the east-facing nature had put them off, being in shade from about noon, but in this hot April it doesn't bother them at all as they are busy into the evening.
With a mixture of holes sizes some are more desirable than others, these two going head to head over this one. Approx 7mm seems best for this species, but other species may have different preferences.
This one is just moving in, removing a wood shaving that I'd thoughtlessly left inside the hole.
A stack of south-facing logs at the bottom of the garden with 7mm holes drilled in them is also proving popular this year with a total of 13 holes already filled. It only takes a few minutes to make a bee hotel this way - give it a go!