We've had Mason Bees in the yurt these last few weeks. Looking for holes to fill with mud. (They're not fussy - I caught one trying to build a mud nest in the top of an envelope.)
In an effort to give them somewhere more suitable to do their thing, Her Outdoors and The Daughter found a mason bee house online you can buy for about €12. However, the website made the mistake of including a picture which I ripped off unashamedly for the cost of eight screws. Here it is (including a hole blocked up with mud):
Now you can rip it off from me.