I removed the tray from under the OMF and it was covered in what looks like small cylindrical pieces of wax. They are about 2mm long and 0.5mm diameter and vary in colour from light brown to black. They have a textured surface, possibly made by a bees mandible, they are too small for mouse droppings and too big for wax moth so I wonder if it's something the bees are doing. I can't say that I've noticed these before, at least not in these numbers so I would be interested to find out what it is.