For the last decade or two we have been told that having open mesh floors under our hives allows not just monitoring of the natural fall of mites but also the removal of a small number of live mites from the hive. However, I now read on Wikipedia that Cornell University has shown that mesh floors are not effective. The snag is that their website says it is being constructed so I’ll have to wait for their explanation.
I have also read that phoretic mites are more fertile than those which emerge from one cell and immediately enter another. It may be that they are older or have enjoyed a more varied diet. Certainly there is the possibility that by parasitizing more than one host a mite will accumulate more pathogens. It is also clear that if a parasitized and poorly bee should fall onto the mesh floor then live mites on that bee will not fall through and will have the opportunity to crawl to passing bees. So, perhaps, there are times when the mesh floors do not offer a net benefit.
As wasps and hornets are now dying I have removed the mesh floor of my Warré hive to allow any weak bees that drop to fall clear of the hive for the greater good, Captain Oates style. Any mice would have a long way to jump and climb to reach the combs and badgers may also find it difficult.
Hives with frames close to the floor would not hinder these pests.
The floor that I have slopes at 30 degrees so that falling bees bounce clear anyway but this exercise is more to see if they will prosper without the floor during the winter for those with conventional, horizontal mesh floors.
Seeing a constant drop of a few dead bees each day over winter is far better than finding a mesh floor covered in dead bees in February.
Remember that the dead do not wait to be counted; many agents work throughout the day to clear their table.