THE FOLLOWING HAS BEEN UPDATED SINCE IT WAS ORIGINALLY POSTED.
Here’s the short version: Take a piece of wood the size of a regular entrance reducer (15 inches / 38.1 cm long). Cut a notch in it that’s at least 1 cm high and 6 cm long (1 cm = approx. 3/8 inch). Drive thin nails in a row inside the notch so there’s 1 cm of space between them. The nails should look like prison bars. The holes in a regular mouse-proof entrance are slightly less than a centimetre wide, so as long as the space between the nails is no wider than a centimetre, this should do the trick. Just make sure to brace it in place with something heavy or nail it down. It doesn’t get any cheaper or simpler. I haven’t tested the design yet, but I’ll update this post in the spring of 2011 and let you know if any mice got in the hives. I think it’ll work just fine. (See also Winter Mouse-Proof Mesh.)
It went up to 14° Celsius in the backyard today (that’s 57° F in Non-Metricland). I have a wireless thermometer set up under one of the hives. 15° during the summer was the magic number that got all the foragers and young bees out of the hive. But the magic number has been 10° since mid-September. The bees in both hives were out in full force. The backyard sounded like one big buzz. Check out how crowded the bees were before I opened their entrances all the way (I’ll post a quick video of it later on in the comments).
While I was out there enjoying the brief blast of warm of air, I decided to build my mouse-proof winter entrance reducers for both hives. That’s one piece of beekeeping equipment that falls well within my limited carpentry abilities.
I had no desire to bang around town looking for quarter-inch wire mesh to cover the openings in the entrance reducers. I came up with a much simpler solution — if it works. There’s no need for details instructions. It goes like this:
Cut a piece of wood that’s about 15 inches long. Slight adjustment may be required to fit individual bottom boards. Then use a jigsaw or whatever you have on hand to cut out a notch that’s about 1cm high by about 6cm long (1cm = 3/8 inch). Then drive some thin nails in a row inside the notch about 1cm apart so that the top of the nails are flush with the bottom of the entrance reducer. If that doesn’t make sense, here are some photos that demonstrate what I’m talking about:
The 1cm space between the nails, like the bars of a prison cell, are just wide enough for even drones to fit through, but small enough, I hope, to keep the mice out.
I might have to pull the nails out a bit to make sure they’re flush with the bottom board before I finally install them for winter, and I’ll probably brace the reducers with rocks on each end to keep them in place, but I think they should do the trick.
If the hole isn’t big enough or the space between the nails is too wide, or if anyone notices anything wrong with my patented design, please let me know in the comments (and I’ll update this post accordingly). Thanks.
UPDATE (Feb. 10/11): If I use these entrance reducers again, I’ll make sure to flip them so the openings aren’t flush with the bottom board. To quote from the Honey Bee Suite: “If you use an entrance reducer during the winter months, it is important to place the opening at the top of the reducer rather than at the bottom… This is so that the entrance does not become blocked by the layer of dead bees that frequently accumulates in cold weather.” I also noticed melting snow above the bottom board blocks the opening with ice.