A new bee hotel and its guests

This year I got a new bee hotel, kindly given to me by George Pilkington from Nurturing Nature. What a great present! His bee hotel design has removable wooden sides with glass covering the actual grooves in the wood, so that you can remove the wooden sides and inspect the cells as they are being built, a rare peek into this usually hidden world. It is designed to provide suitable nesting holes for the common Red Mason Bee, Osmia rufa, which would naturally would use holes in masonry or cracks on walls to nest.
  I treated the nest with teak oil before hanging it out in early February (above). The Red Mason Bees took to it quite quickly after their appearance in the garden, and on the 11 of April the first female Red Mason Bee Osmia rufa roosted in one of the holes.

Below, a male here inspecting the hotel (14/04/14)

By the 10th of May the topmost hole had been sealed and the second had a couple of cells already made.

a poor photo showing the row of cells containing a mound of pollen, nectar and an egg laid atop. Each cell has a mud wall separating if from the following one (10/05/14).

Once a hole has been filled with cells the bee puts the final wall to cover the nest. This is the first finished row of cells.

On the 12th of May, I spotted the first beautifully fresh and golden Male Osmia caerulescens, sitting on the conservatory window by the sage. The males have been about about a week now, and females a couple of days. Males are very similar to Osmia leaiana males, but O. caerulescens have a strong preference for sage and hedge woundwort in my garden, while leaiana prefers knapweed.

...and the same day this very old, faded and bald male Osmia rufa  guarding the bee hotel.

A cleptoparasite fly Cacoxenus indagator is also present often around the bee hotel. This little fly, related to fruit flies, parasitises Red Mason Bee nests. The fly will lay eggs on the cell as a bee is provisioning it. Its grubs will feed on it, preventing the development and emergence of the bee (17/0514).

This female Osmia rufa is finishing filling the second hole.

On the 17th of May I also noticed a new bee (so I thought!). It turned to be a wasp, Sapyga quinquepunctata, which is a cleptoparasite of solitary bees including from the genus Osmia, the mason bees. I found this wasp on the nest and surrounding area. It has blue-purplish wings and white spotted abdomen, with curved antennae. Thank you to Ian Beavis who identified it from one of my photos on Twitter.

Another view of the wasp, on the post holding the nest. The wasp is also a cleptoparasite of Osmia and related bees.

The bee hotel today. Four cells have been completed.

Not only the bee hotel makes it easier to observe mason bees, but other bees and their cleptoparasites will also be attracted to it, increasing the chances of observing their development in the nest and interactions. Also to note that a spider, possibly Clubiona sp, has made a home in one of the holes.
Undoubtedly, I will post more on future developments on this bee hotel.