I was given a Bee apartment house at Christmas by my grand children and within four weeks tenants had taken up residence, but it seems so far they are wasps.
Two species have taken advantage of the ready made nursery, with the two grass filled tubes at the top, the nests of a Grass Carrying Wasp. I haven't seen the wasp so the identity is not known, although it is likely to be a species of Isodontia (the only reference I have found is for an American species, Isodontia mexicana, however it is reportedly also found through Pacific islands)
Two tubes lower left had been filled in by a Mud-nesting Wasp.
I saw a wasp at the tube two days ago and managed to get a couple of photos (not too sharp) and the identity likely to be a Black Mud-nesting Wasp Hyleoides concinia.
Today a wasp was just putting the finishing touches to its new nest in the tube from where the wasp (2nd photo) is emerging.