Is it necessary to have a mouse guard at the opening of the hive, and if so where can you buy them and does anybody know how to make them:?
I use 1/4 inch hardware cloth for any empty boxes (deadouts), and wooden reduced entry way for the live boxes.
Hardware cloth as mentioned (most people bend it in a V and shove it in the entrance, just remember that if you can slide a pencil in by an edge, a mouse can squeeze in), or most suppliers have mouse guards. They are adjustable and sturdy. They have holes every inch or so for the bees to come and go. I also use them on weak hives as entrance reducers (I have screened bottom boards, so I don't have to worry about ventilation) I just duck tape over the holes and leave one hole. Then as they get a little stronger open it up to two, etc. You will only have to get one mouse in a hive in the Winter to convince you that you need a guard. It is pretty much just a Fall and Winter issue.
JC
This past fall I started with new entrance reducers reducing the entrance to no entrance. That is blocking the the entrance 100%. I then drilled two 3/8 inch holes through it so the bees could get in and out but not mice. I do worry about them getting pluged every time I see them but so far it seems to be working well. I had mice in one of three hives last winter even though I though I had the entrance to tight. I belive the pencil analogy may be true. The little suckers can get into just about anything.
It would be best to just block the entrance completely like MB and drill a hole in your second box or make a top entrance but I just dont like the idea of holes in my boxes but next year I think Im just going to do it.
How big of a hole do you suggest
Something you can't slide a pencil in! :-D But seriously, 1/4" to 3/8" does seem about right. I didn't make up the pencil idea - I have a friend who is an exterminator (the good kind that calls beekeepers) and that is the rule of thumb that they use. If the pencil end with the metal eraser end goes through easily, a mouse will squeeze through. I guess it has something to do with if their skull will fit through the rest can follow.
JC
I would recommend using an inner cover with a notch cut out and then just push your telescopic cover forward so that they can use that as the upper entrance instead of drilling holes in your boxes.
Question for those of you that do use them. When do you normally take them off? I use an upper entrance and then I've been using 1/4" hardwire for the bottom entrance...if there is one thing I don't really like about it, it's that the bees have a hard time removing the dead from behind it...they build up to the point that I've got a couple houndred dead bees behind it and I have to open it up and scrape them all out. I was thinking about removing it soon.
using a notched inner cover is not a bad idea. But for me its the same as drilling wholes in my boxes. My main concern though is about having to make sure you leave room for the bees to get out of the notch and having to make sure the notch is down and to the front........ I dont have time for all that crap. If you have a couple hives, its a good way to go.
And yes it is the mouses skull size that determines what they can get into or not. Same as a cat. Cats can get through smaller holes that you would think. I dont think many mice will get through a 3/8 hole. Maybe a half grown field mouse but not a normal one. I would say you are pretty safe with a 3/8 inch hole. As soon as the bees are out of there winter cluster mice are no a problem any more. Bees do not like mice, let me tell ya. I use hive top fondant feeders. Last winter I had some mice living under one of the telescoping lids. When i took the lid off one ran under the felt. When I got the felt open and toll the inner cover off it got in the hive top feeder where the cluster was and I watched two or three bees jump on and drill that mouse and you should have seen it jerk with each sting, it was great. Sorry if you find it sick but I would have loved to see that mouse get stung to death, like three hundred times. That would have really made my day and a great you tube video to share.
A mouse can enter anything larger than a dime size hole. I learned that lesson last year.
Back before I went to top entrances, I used 1/4" hardware cloth. But March isn't the time to put mousegaurds on. You're more likely to trap them inside than keep them out... Put them on in the fall as soon as it starts to get frosty enough for the bees to be clustering.