Busy bees (2)

Red mason bees (Osmia bicornis) nesting in my "bee hotel". Visits to cap a cell with mud are quite short, but visits to fill a cell with food take a minute or more. The cell second from the left on the bottom row appears to be in use by two bees.

Sorry about the poor focus. My 500 mm mirror lens has very shallow depth of field and is also quite difficult to focus.