One of the talks I attended recently was by Derek Mitchell entitled “Honeybees and Mosquitos”. An intriguing title, and it turns out the Mosquitos were those twin engine planes of WW2, and not the blood-sucking kind.

The link between the two is to do with our beehives and the specification of the Standard National hive. A gross simplification of the talk is that the war requirement for wood of all sorts meant the thickness of wood used for our hives was reduced, and it was better used for Mosquitos.

In the wild bees colonise the hollows naturally formed and those excavated by woodpeckers. The walls of these hollows have to be quite thick because they still have to support the tree above, whereas our hives are made of planks barely 1 cm thick. The thicker the wood the better the insulation: wood is a very good insulator. Better insulation means the bees do not have to work as hard in winter to keep the colony at the required temperature, and hard work means food, i.e. honey. Well insulated bees use less honey through a winter than bees in a thin-walled hive.

That made sense to me, so I made a brood box out of scaffolding planks. The wood is much thicker so it ought to be much warmer for the bees. Unfortunately it was also so heavy I could barely lift it when empty! We use cedar for a very good reason. Polystyrene hives are gaining popularity, but I am not keen on using plastics for my beehives.

The bee cosy of the title turns my 14 x 12 Nationals into an insulated WBC for the winter. It is a box that fits snugly around my National brood and supers and it allows me to insulate with 50 mm (2 inch) of sheep wool insulation all the way round, and on top. I could use polystyrene, but it is a plastic, it is ugly (my wife has casting vote) and it is not weatherproof. Foil-backed insulation is better for weatherproofing, but it is even uglier and the foil makes it non-permeable, i.e. water vapour cannot escape through the walls, whereas wood and wool do allow water vapour to pass through. High humidity levels in the hive are a natural result of bees metabolism and evaporating nectar to make honey. That is not a problem, providing the water vapour does not condense. The inside of a thin wood wall may be cool enough to allow condensation to occur, and that is not good for bees. Thicker wood walls will reduce the chance of condensation, but then we cannot lift our beehives because they become like hollowed out tree trunks. There is evidence that higher humidity levels in the brood (> 95%) is detrimental to varroa propagation, but such high humidity makes the chance of condensation in our thin walled hives more likely.

I install the bee cosy after my last inspection of the year and take it away in spring when I want / need to do regular inspections. The cosy is a tight fit around the brood box so as to exclude draughts, but that also means I cannot easily remove a super or brood box, not at all, in fact. I can fit and remove an eke and cover / crown board so that allows me to feed or treat the bees, but nothing more. Not that I need to in winter. The roof is also well insulated with sheep wool; a double layer of up to 100 mm thickness. That way fondant on the cover board stays warm and soft and liquid feed (if I were to use it) will not freeze. The bees are happy to take the fondant through the oval hole of the Porter bee escape because the fondant is as warm as the top of the brood box. The advantage for me is that I do not have to lift the cover board to put more fondant on and the bees do not all rush out at me on a cold day.

The cosy is made like a small shed with four sides all nearly equal and held together by screws. The sides go all the way down to the stand and support the “floating” front and back. The front and back are shorter to allow the bees entrance to the hive, and the short back allows me to insert and remove a floor for varroa drop monitoring. It takes about 10 minutes to install the cosy. My first cosy had the wool just loose around the hive and gravity won the day by all the wool falling down at my feet. Now the wool is retained in a 50 mm high frame with a light mesh over the top. The photographs below will make it clear, I hope.

The outer skin of the cosy is ordinary shiplap timber. I chose the thicker planks of the two types available. At 19 mm it is as thick as my hive. The cosy sides are made up on a 50 mm thick frame – think of an over-sized eke, with planks pinned and glued to the frame. The frame also holds the wool in place and prevents it crushing. It sounds complicated, but it is not. A picture is worth a thousand words, so see below.

The dimensions will vary with the type of hive used. It is important the cosy is a reasonably tight fit around your hive, otherwise draughts will defeat the object of having the insulating layer.

If you are interested in more details then please get in touch and I’ll give any information I have. I have some sketches, but they are “working documents”, i.e. pretty rough.

Bert Laan                                        training@swhbk.org.uk