Mouse guards, woodpeckers and insulation over winter

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Damp kills bees, not cold

The National Bee Unit puts it in one sentence. It is the damp, rather than the cold, that kills bees. 1 Everything else on this page follows from that.

Bees make a great deal of water vapour as a by-product of metabolism, and it condenses on the cool hive walls. 1 The water has to get out. If it cannot, it runs back down onto the cluster.

So the NBU asks for the hive to be set up to let the water run out of the entrance, either by slanting the hive very slightly forwards or by having the floor inserts removed. 1 Ventilation from the roof, entrance and floor is usually sufficient. 1

On an open mesh floor the insert can come out for the winter, unless your apiary site is vulnerable to windy conditions. 1 That caveat is easy to skip and it matters. Tray out on a sheltered site. Tray in on a bare hilltop.

The aim is a dry hive, not a warm one. Warmth is what you get for free once the damp is dealt with. The last look before winter covers the rest of that check.

Insulation over the crown board

Start with what the source actually says, because it is narrower than most people quote. Insulation may be used in areas that experience particularly harsh winters, provided good ventilation is maintained. 1 That is permission rather than a prescription, and no thickness is given.

The BBKA is a little warmer about it. Its October entry says to consider adding insulation at the top of the hive. 2 Again with no figure attached.

House practice here goes further than either of them, and it is only fair to say so. We put a 50 mm sheet of rigid board in the roof space, on top of the crown board, on every hive from October until spring. Not only in a hard winter. Not only on a hard site.

The reasoning is that the coldest surface then sits above the insulation instead of directly over the cluster, so the condensation forms on the walls and runs away. That is our result on our own hives. It is not National Bee Unit guidance and we are not going to dress it up as any.

What we do not do is seal the hive up. The board covers the crown board hole and nothing else. The floor and the entrance stay exactly as they were, because keeping the ventilation is the condition the NBU attaches to insulation in the first place. 1

Wrapping the outside of the hive

A normal British winter does not need a special wrap. Ventilation from the roof, entrance and floor is usually enough on its own. 1 A wrap that holds moisture against the woodwork builds the exact problem you were trying to avoid.

Our answer on most sites is not to bother. If you do wrap, use something that breathes, leave the entrance and the floor completely clear, and take it off in early spring. That is ours, not guidance.

One thing a wrap will not do is stop a woodpecker. A sheet or a feed bag in contact with the box gives the bird something to drill through, not something that keeps it away. The barrier that works is in the section below, and it does not touch the hive at all.

Mouse guards, and the hole size question

A mouse in a hive over winter is not a nibble at the comb. It nests in the brood box, fouls the stores and wrecks the frames. The NBU asks for mouse guards to be fitted to prevent access by small rodents, which often nest in hives during the winter, and says plainly that mice can kill colonies during winter. 1

What the NBU does not give is a dimension. There is no official UK millimetre figure for this, and a guide that prints one without saying where it came from has invented it.

The standard product settles it in practice. Thorne’s galvanised mouseguard is a strip of 470 by 38 by 0.5 mm punched with two rows of 10 mm holes, held across the entrance of a standard floor with drawing pins. 3 It fits every hive except a WBC, which has one of its own. 3

So 10 mm round holes keep mice out. That is a manufacturer’s specification rather than a study, but it is the figure the whole country buys to, and it works.

A reduced entrance slot is a different test, and this is where people get caught out. A mouse flattens sideways, so it passes a long low gap more readily than a round hole of the same height. A slot therefore has to be lower than a guard’s hole, not equal to it.

We cut ours to under 8 mm and it has held. That figure is ours. We cannot point you at a published one, so please treat it as house practice rather than a standard. If you would rather not judge it by eye, buy the guard.

• A metal guard pinned across the entrance. The standard answer, cheap, and the bees learn it in a day. 3
• An entrance block cut down to a slot. Fewer obstructions for the bees, and it doubles as wasp defence into September. Wasps and robbing covers that side of it.
• An underfloor entrance, which most mice will not use. Ours, and not a guarantee.

The timing is not ours. The BBKA puts the job in October: fit mouseguards and turn entrance blocks upside down. 2 Fit them before the first hard night. A guard fitted after the mouse is in has shut it in there with the bees.

They come off again in March, once the frosts have passed. 2 Thorne says the same in plainer words, which is that guards are removed in the spring. 3

Then keep the entrance clear. The BBKA asks for dead bees to be cleared from entrances through January and February so they do not block them. 2 Use a stick from the outside. Nothing needs opening for that.

Green woodpeckers: the cage, and the 300 mm

Green woodpeckers work hives in prolonged cold, when the ground is frozen hard and the ants are out of reach. A wooden brood box wall does not slow one down.

The NBU gives one answer and it is specific. Where the damage is a known problem in or near your apiary, place a simple cage of chicken wire around and over the hive, and place that wire at least 300 mm from the hive walls, to prevent damage whilst still permitting bees to fly. 1

Read the distance twice, because it is the half that gets dropped. Mesh hung against the hive is not this. A bird can reach through wire that touches the box and drill the wood behind it. The gap is the whole mechanism.

The BBKA agrees on the shape of the answer. Its October entry suggests a wire cage around hives where green woodpeckers are a problem, and its January entry says mesh cages can prevent woodpecker damage. 2

A barrier is the only route open to you, because the bird is protected. Under section 1 of the Wildlife and Countryside Act 1981 it is an offence to intentionally kill, injure or take any wild bird. 4 A green woodpecker is a wild bird.

The extent matters if you are not in England. That version of section 1 covers England and Wales, with a separate version made for Scotland. 4 Northern Ireland has its own instrument, article 4 of the Wildlife (Northern Ireland) Order 1985, and that one catches reckless acts as well as intentional ones. 5

So build something that stands up on its own and stands clear. Loose netting draped over a hive is not a barrier, and it is a trap for the bird you are not allowed to harm. Check the bees can still fly before you walk away.

Whether you need one at all is a local question. Some areas never see the damage. Others lose a hive most hard winters. Ask people who keep bees within a few miles of you, because it varies over a surprisingly short distance.

The chicken wire is on the autumn kit list, with the same 300 mm figure.

The order it goes on

None of this is a September fitting job. September is the last call for having the kit in the shed, and the buying should have happened well before it.

Order it with the rest of the autumn list in July or early August. The kit list guide says the same for the same reason: a mouse guard is no help once the mouse is in.

The sequence below is our own. The dates inside it are the BBKA’s and the NBU’s.

• Finish the feeding first. Bees may be unable to process syrup to store it properly beyond mid-October, and fondant takes over from there. 1 The BBKA stops syrup early in the month. 2
• Insulation when the feeder comes off, not fitted around it.
• October: guards on, entrance blocks turned. 2
• The woodpecker cage in October too, where your area needs it, rather than waiting for a hard forecast.
• Do the lot at the last full look, so the hive is opened once rather than three times. The last look before winter is that visit.
• March: guards off once the frosts have passed. 2

When the simple rule breaks down

• Poly hives. Already insulated, so the board over the crown board matters less. Go easy on the straps, because overtightening ratchets can damage a polystyrene hive. 1
• Nucleus colonies. A small cluster has a greater surface area to volume ratio and loses more heat per bee. 1 Do the nucs first, not last.
• Exposed windy sites. Leave the floor insert in. Wind is the NBU’s own exception to taking it out. 1
• A colony light in late October. Fondant, not syrup. Syrup should not be fed in winter, because it is too cold for the bees to use and it grows mould in the feeder. 1 Starvation and emergency feeding has the method.
• A WBC. The standard guard does not fit it, so order the WBC one. 3
• No woodpecker history near you. Skip the cage and put the money into a sound roof instead. That is ours.
• A mild southern site. Bees may still be flying in December. The guard still earns its place. A wrap still does not.

The short version

• Damp kills bees, not cold. 1
• Keep the ventilation. Roof, entrance and floor is usually enough. 1
• Mesh floor tray out over winter, unless the site is windy. 1
• The NBU permits insulation where winters are particularly harsh, provided ventilation is maintained, and names no thickness. 1 Our 50 mm board on every hive from October is house practice, not guidance.
• Mouse guards stop rodents that nest in hives and kill colonies. 1 The standard guard is two rows of 10 mm holes. 3
• A reduced slot has to be lower than that, because a slot is not a round hole. Ours is under 8 mm and that figure is ours alone.
• Guards on in October, off in March when the frosts have passed. 2
• Woodpeckers: a cage of chicken wire around and over the hive, at least 300 mm clear of the walls, still letting the bees fly. 1
• The bird is protected, so a physical barrier is the only answer. 45
• Buy the lot in July or August with the rest of the autumn list.