I am not quite sure what is going on here. When I first started watching the bee box, the end of the tube in the nest hole was covered with what I assume to be pollen (rich, golden yellow). Then this bee came along and pulled away a large chunk, flew off, came back a short while later (well, I don't really know for sure it was the same one) and tore off more and then that was that.

ID to species is thanks to John Ascher.