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Using Open Mesh Bee Hive Floors
This text was mainly written by Ken Hoare (Shropshire, but now in Wales) and reproduced with his permission.

Help your bees with OMF's.

Have you ever suffered winter losses, maybe observed signs of faecal staining on the front of the hive, or the combs themselves? How about mouldy combs, generally the outer or flank ones, or mouldy pollen? Alternatively, problems with wax moth, both the Lesser Wax Moth (Achroia grisella) and Greater Wax Moth (Galleria mellonella).

Ensuring the interior of the hive is both dry and well ventilated can reduce all of these problems and the easiest way to achieve this is to use 'Open Mesh Floors' (OMF's or screened bottom boards).

Maybe new to you, but well documented in articles such as 'Observations on the Overwintering of Honeybee Colonies in Hives with OPEN and SOLID Floorboards' by Helmut Horn and reproduced in the July 1990 issue of Beecraft. What are OMF's? Simply a floorboard where the solid wooden section is replaced with a sheet of wire mesh, virtually leaving the bottom of the hive open to the elements.

But my bees will get cold, maybe even die of frostbite during a hard winter you will say. Sorry to disagree, but generally bees do not die of cold, it is damp conditions that cause bee deaths. This can be verified by beekeeping friends from North American, Canada, and many of the colder European countries who regularly use these floors, sometimes having to dig their hives out from deep snow to discover all is well within the brood box. The next question will be that other bees and wasps could easily rob the hive. Might be true if you use the wrong size mesh, but I will describe the type needed later in this article.

During the early 1990's beekeepers throughout the UK were invited to test these floors. I joined these trials and without listing the findings of the experiment hopefully it is sufficient to say the majority found their colonies loved all this additional ventilation. My trials on just three hives, at that time about 10% of my stocks, supported the findings of others, my bees adored OMF's, both summer and winter.

Then in 1992 the Varroa mite arrived in the UK and I was asked by the Bee Inspector to strictly monitor for its arrival in Shropshire. This meant returning to solid floors, a paper or similar insert placed on it, and a Varroa screen above. But what is a Varroa screen, simply another name for an OMF. Using this method I did discover what I believe was one of the first findings in South Shropshire, just one mite found on the insert.

But my colonies started to attract wax moth, both types, who found a safe haven below the mesh screen where bees were unable to gain access. So I removed the screens, returned to solid floors and again suffered from damp conditions. If you use floorboards that have been freely treated with a wood preservative you will have noticed that if the hive level should fall towards the back (bad beekeeping) a pool of water, or damp hive detritus will collect.

So I quickly returned to OMF's, and currently I'm in the process of adapting them so both ventilation and Varroa monitoring can be achieved without suffering the problems already mentioned.

Another advantage of OMF's is they can be used as part of an Integrated Pest Management regime in the control of Varroa mites. It is well documented Varroa mites drop off the bees, it is suggested this can be encouraged by sprinkling icing sugar or talcum powder over them so they loose their grip on the adult bee. Some will fall onto a bee lower down the comb, but some will eventually reach the floor. If this is of the solid type the mites can easier climb back onto the comb, but given a mesh they fall through to be devoured by ants and the like. Part of a Varroa control programme and all without the use of chemicals. It is essential to add these floors cannot be the sole method of mite control, just part of the Integrated Pest Management regime previously mentioned.

And it is documented as many as 40 - 60% of the mites can be removed from the hive using this method. This figure is disputed, but I will be perfectly satisfied with loosing 10% of my mites given they have the ability to multiply themselves a thousand fold each year. The method is also promoted in the latest UK Ministry of Agriculture leaflet titled 'Managing Varroa' where they emphasis this is a method which can be used throughout the year.

Still sceptical? What will a bee do with an opening it objects to, we all know the answer is they will fill it with propolis. Place a piece of mesh over the feed hole and I guarantee it will quickly be sealed with propolis. But I have never encountered an experience of bees fixing anything to the mesh, occasionally a small piece of propolis will be found affixed, but this has obviously dropped from the bees located above, the heat of the hive welding it to the wire. Sealing of the mesh has been reported by another OMF user (Tim Kidman from Cheshire) but he informs me the bees removed it all before winter set in. Never have I witnessed comb being extended from the bottom of the frame and fixed to the mesh, if you think about it this would compromise the security of any brood or food. This point alone makes colony examination so much easier.

Recently I have heard beekeepers state the queen fails to lay to the bottom of the comb, whether she is trying to avoid the light, or maybe she finds it a little exposed they have been unable to establish. Personally I have not found this occur, well at least I have not noted it but for the coming season I will take careful observation. I have been asked whether comb is built to the bottom bars of the frame and the answer is a definite yes, I would have noted if they failed to do so this being a pet hate of mine. I give them good foundation and they chew a hole along the bottom, no I would have noted that.

Another of my passions is a small hive entrance knowing a gap of nearly 18" (450 mm) wide needs a lot of bees to guard it. But give them a small entrance on a hot summer's day and bees will congregate outside the hive, what the Americans term as 'bearding'. No problem with OMF's, obviously plenty of ventilation is available irrespective of entrance size. Locally a new beekeeper made a five-frame nucleus hive incorporating an OMF. The entrance was a 3/8" (9 mm) drilled hole, a little too small, maybe three such holes side by side would have been better, but even during warm spells bees have never clustered at the entrance.

I am not suggesting you should change all your solid floors to the open mesh type, instead I am trying to encourage you to give them a small-scale trial. Maybe for the two-hive beekeeper this will mean using 50% of their colonies, one on a solid floor, the other on open mesh.

Constructing an OMF is simple; a wooden framework of hive dimensions is constructed, and to this is fixed a sheet of mesh. A small entrance is incorporated into the wooden surround.

The drawing, Open Mesh Floor to suit National is self-explanatory.

Starting with the mesh, I have already stated the dimensions are critical, too small a mesh and the mites will not drop through, too large and the security of the hive has been compromised.

Mesh of 8 wires to the inch is required. Given the thickness of the wire this gives squares of just under 1/8", a perfect dimension. Such mesh can be obtained from E.H.  Thorne (Beehives)  Ltd. This is a black epoxy coated and an 18" (460 mm) square piece will fit a B.S. National or B.S. Commercial hive. The problem I find with this mesh is although propolis and comb is seldom fixed to the wire I still like to wipe the flame from my gas torch across it and obviously the coating quickly burns off leaving bare metal to rust.

Galvanised or stainless steel mesh is best although the latter is extremely expensive. Suitable galvanised wire mesh can be purchased from Locker Wire Weavers. Since I purchased my original mesh they are enforcing a 'minimum order' rate, but provided you can get sufficient beekeepers to co-operate mesh of suitable size can be purchased inexpensively. Alternatively a Dublin company known as The Expanded Metal Company, Tel: 01 6265981 Fax: 01 6267802 Email: expamet@tinet.ie are offering a stamped galvanised sheet at a price that could be less than 1 for the National hive size. Probably not as good as woven mesh, but then the price is more favourable.

Generally all the above requirements are found in old fire guards, well maybe not the galvanising, but if you have recovered them free of charge from a builders skip what does that matter.

It must be remembered the mesh will not support the weight of the hive, and hopefully many full supers, such weight should be borne by the wooden framework of the floor. I have made 15" (375 mm) high hive stands, so much easier on the back, and the floor rests on each of the legs. When using OMF's it is recommended the floor be at least 12" (300 mm) above the ground. I have one OMF standing on a milk crate, but have placed a couple of wooden bearers across the top of the crate onto which the floor then rests.

When monitoring for Varroa 'Natural Mite Mortality' with my original OMF's it necessitated sliding a solid floor and insert below the mesh floor, 'humping' I could well do without. But by adding deeper sides it allows me to cut a grove into those sides into which I can slide a sheet of thin painted plywood or hardboard. When monitoring is needed these sheets are slid into position and removed once the simple task is accomplished. Don't leave these boards in longer than necessary as you are defeating the objectives of OMF's.

The floor of the WBC hive can be adapted into the open mesh type, simply cut out as large a section of the timber as possible and substitute it with wire mesh. Maybe the remaining timber of the floor will need strengthening with some 2" x 1" (44 mm x 18 mm) battening. Again it will be advisable to raise the height of the hive, but this can easily be achieved by placing the legs on concrete building blocks - also reducing the amount of rot to those legs.

Although the floor is used throughout the year it is advised top insulation be given during the winter. This is achieved by adding about 3" (75 mm) of good insulation above the crown board and surrounded by a wooden eke (four pieces of timber nailed together to form a square, or an empty super will act as a substitute). Such insulation will reduce the amount of condensation forming on the inside of the crown board. A further recommendation is the crown board is not removed, and propolis seal broken, after the supers have been removed, but with Varroa strips to be removed towards the end of October I find this impossible.

These floors are best added in May or June as this gives the bees a little time to acclimatise to the change before winter sets in. So early this year I urge you to give OMF's a trial.

Ken Hoare.


One additional note about breaking the propolis seal...Some have used masking tape to deliberately seal the gap between crown board and hive top. However even with my unusual insulated roofs that do not need a crown board... Water ingress is not a problem although I expect a small amount of air leakage occurs.

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Originated... Autumn 2000, Revised... 25 January 2003,