Leaf cutter bee's cocoons

We were given this 'bee and insect hotel' several years ago and hung it up on a dead limb of the old rhus tree, where previously we'd hung bird feeders.

I've occasionally looked at it and noticed it was becoming more weathered, and probably more attractive to any possible insects. I wsa never sure such an idea would work. A few years ago this same tree did have a leafcutter bee's nest in a hole in its trunk, but that has become very exposed and redundant.

Today I saw that three of the holes's ends had become blocked up and oj close inspection I could see that the leaves of a cocoon had been used. One oif the holes seems to have now been cut through, so I don't know whether that was an grub emerging or an invasive attack by a predator. But it proves that the bee does use man made shortcuts, so I should encourage them by providing more in future. I fear they need all the help they can get.