About 3 years ago we were given a little house for solitary bees. We put it on a fence, facing south, but it was shaded by a neighbour’s trees. For the first year, it was empty, then the neighbour cut the trees right back and it was in sun.
Year 2, it had 2-3 inhabitants. Then the other day (now year 3) we noticed it was really buzzing with activity.
Let me put that another way. We screwed this to the fence three years ago and did nothing since. We now have a mini colony of bees living in it. All it needed was patience (and sun – important for solitary bees). You too could have a colony of pollinators in your garden for the same amount of effort! Even a tiny garden can find room for one of these. What’s more, note the round bum of these bees. Solitary bees do have a sting, but it’s too feeble to penetrate human skin, and besides they’re not interested in defending their nest – they simply pack it with food and leave the young to fend for themselves.
You can make a solitary bee “hotel” simply by drilling holes in a log.
I think they’re mason bees, but as there are over 100 species of solitary bee in Oxfordshire I wouldn’t put money on it.