I’ve just made a Varroa floor for the National Trust’s new National hive at Hardy’s Cottage as I’m not satisfied with those available commercially. They all have the collecting tray far too close to the mesh. Dr Jeff Pettis in the USA studied Varroa floors and the actions of healthy mites that had fallen through by accident or grooming, rather than those that were damaged or had died of old age. When the collecting tray was half an inch below the mesh floor, all the healthy mites got back into the hive: when the tray was 2″ below, none got back. There was a range of returning success/failure as the depth increased.
Therefore my very simple design has a 2″ plinth, surmounted by the mesh, held in place by a quarter inch rim with a gap at the front for the hive entrance. The rim is deep enough to provide bee space and reduce the tendancy for bees to add comb beneath the brood frames and is shallow enough to keep out virtually all mammalian predators and maybe even a few insects also.
The Varroa floor will sit on the National floor provided, but it will face towards the rear of the hive and will give access to the sheet of corrugated plastic to be used as a tray to catch, count and examine fallen mites and other debris. I haven’t done that bit yet. I shall mark it into squares for easy counting.
It has had 2 coats of clear Cuprinol so far and I shall add another this morning. That should delay the rot for a while and any smell will be well gone by the time it is put into use.