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