Monday Mystery

Apologies if some mystery close-ups are getting more difficult.
I am finding it harder to think of new subjects to photograph.
I often don't find something until almost the last minute.
So it was with last week's mystery:



Congratulations to Adrian, Dave and Kev for spotting it was



an insect hotel.  This one has been up for several years and never seemed to show the result of any activity apart from spiders' webs. The previous weekend I was idly pulling up a few weeds nearby when I heard constant buzzing. I finally located it near the insect hotel. A mason bee was making repeated trips to the same hotel 'room'. I'm fairly sure this is a Red Mason bee.



I also noticed some of the holes were plugged with dried mud and some were partly open. The closed ones should have mason bee cocoons and the partially open ones are probably where hatched bees have made it out to the wild world.

I also took a short piece of video of the bee when it visited the hotel:



One reason it may have become popular with the bees is that I moved it. It used to be somewhat in the shade but I recently read the mason bee prefers South facing sunny locations which is where it is now. They are common in lowland areas of England and Wales. Seen mainly from April to July. They feed on Spring flowering shrubs and particularly on apple and pear tree blossom (several fruit trees next door) as well as cultivated flowering plants. Instead of having pollen bags on their legs the female Red Mason bee collects it between hairs on her abdomen.

And now, as they say, for something completely different



which is part of ... what?

Think you know? Want to have a guess?
Please leave any guesses in the comments.
They will be revealed, along with the answer, next Monday.