Winter covers and colony survival

Synopsis : A recent study shows increased overwinter colony survival of ‘covered’ hives wrapped in Correx and with insulation under the roof. What provides the most benefit, and are the results as clear cut as they seem?

Introduction

A recent talk by Andrew Abrahams to the Scottish Native Honey Bee Society coincided with me catching up my 1 backlog of scientific papers on honey bees. I’d been reading a paper on the benefits of wrapping hives in the winter and Andrew commented that he did exactly that to fend off the worst of the wet weather. Andrew lives on the island of Colonsay about 75 km south of me and we both ‘benefit’ from the damp Atlantic climate.

The paper extolled the virtues of ‘covered’ hives and the data the researchers present looks, at first glance, compelling.

For example, <5% of covered hives perished overwinter in contrast to >27% of the uncovered control hives.

Wow!

Why doesn’t everyone wrap their hives?

However, a closer look at the paper raises a number of questions about what is actually benefitting (or killing) the colonies.

Nevertheless, the results are interesting. I think the paper poses rather more questions than it answers, but I do think the results show the benefits of hive insulation and these are worth discussing.

Bees don’t hibernate

Hibernation is a physiological state in which the metabolic processes of the body are significantly reduced. The animal becomes torpid, exhibiting a reduced heart rate, low body temperature and reduced breathing. Food reserves e.g. stored fat, are conserved and the animal waits out the winter until environmental conditions improve.

However, bees don’t hibernate.

Winter cluster 3/1/21 3°C (insulation block removed from the crownboard)

If you lift the lift the roof from a hive on a cold midwinter day you’ll find the bees clustered tightly together. But, look closely and you’ll see that the bees are moving. Remove the crownboard and some bees will probably fly.

The cluster conserves warmth and there is a temperature gradient from the outside – termed the mantle – to the middle (the core).

If chilled below ~5.5°C a bee becomes semi-comatose 2 and unable to warm herself up again. The mantle temperature of the cluster never drops below ~8°C, but the core is maintained at 18-20°C when broodless or ~35°C if they are rearing brood. I’ve discussed the winter cluster in lots more detail a couple of years ago.

The metabolic activity of the clustered winter bees is ‘powered’ by their consumption of the stores they laid down in the autumn. It seems logical to assume that it will take more energy (i.e. stores) to maintain a particular cluster temperature if the ambient temperature is lower.

Therefore, logic would also suggest that the greater the insulation properties of the hive – for a particular difference in ambient to cluster temperature – the less stores would be consumed.

Since winter starvation is bad for bees (!) it makes sense to be thinking about this now, before the temperatures plummet in the winter.

Cedar and poly hives

I’m not aware of many comparative studies of the insulation properties of hives made from the two most frequently used materials – wood and polystyrene. However, Alburaki and Corona (2021) have investigated this and shown a small (but statistically significant) difference in the inner temperature of poly Langstroth hives when compared to wooden ones.

Poly hives were ~0.5°C warmer and, perhaps more importantly, exhibited much less variation in temperature over a 24 hour period.

Temperature and humidity in poly and wood hives

In addition to the slight temperature difference, the humidity within the wooden hives was significantly higher than that of poly.

The hives used in this study were occupied by bees and the temperature and humidity were recorded from sensors placed in a modified frame in the ‘centre of the brood box’. The external ambient temperature averaged 0°C, but fluctuated over a wide range (-10°C to 20°C) during the four month study 3.

Temperature anomalies

Whilst I’m not surprised that the poly hives were marginally warmer, I was surprised how low the internal hive temperatures were. The authors don’t comment on whether the ‘central’ frame was covered with bees, or whether the bees were rearing brood.

The longitudinal temperature traces (not reproduced here – check the paper) don’t help much either as they drop in mid-February when I would expect brood rearing to be really gearing up … Illogical, Captain.

The authors avoid any discussion on why the average internal temperature was at least 5-8°C cooler than the expected temperature of the core of a clustered broodless colony, and ~25°C cooler than a clustered colony that was rearing brood.

My guess is that the frame with the sensors was outside the cluster. For example, perhaps it was in the lower brood box 4 with the bees clustered in the upper box?

We’ll never know, but let’s just accept that poly hives – big surprise 😉 – are better insulated. Therefore the bees should need to use less stores to maintain a particular internal temperature.

And, although Alburaki and Corona (2021) didn’t measure this, it did form part of a recent study by Ashley St. Clair and colleagues from the University of Illinois (St. Clair et al., 2022).

Hive covers reduce food consumption and colony mortality

This section heading repeats the two key points in the title of this second paper.

I’ll first outline what was done and describe these headline claims in more detail. After that I’ll discuss the experiments in a bit more detail and some caveats I have of the methodology and the claims.

I’ll also make clear what the authors mean by a ‘hive cover’.

The study was conducted in central Illinois and involved 43 hives in 8 apiaries. Hives were randomly assigned to ‘covered’ or ‘uncovered’ i.e. control – groups (both were present in every apiary) and the study lasted from mid-November to the end of the following March.

Ambient (blue), covered (black) and control (dashed) hive temperatures

There were no significant differences in internal hive temperature between the two groups and – notably – the temperatures were much higher (15°-34°C) than those recorded by Alburaki and Corona (2021).

All colonies, whether covered or uncovered, got lighter through the winter, but the uncovered colonies lost significantly more weight once brood rearing started February. The authors supplemented all colonies with sugar cakes in February and the control colonies used ~15% more of these additional stores before the study concluded.

I don’t think any of these results are particularly surprising – colonies with additional insulation get lighter more slowly and need less supplemental feeding.

The surprising result was colony survival.

Less than 5% (1/22) of the covered hives perished during the winter but over 27% (6/21) of the control hives didn’t make it through to the following spring.

(Un)acceptable losses

To put these last figures into context the authors quote a BeeI Informed Partnership survey where respondents gave a figure of 23.3% as being ’acceptable’ for winter colony losses.

That seems a depressingly high figure to me.

However, look – and weep – at the percentage losses across the USA in the ’20/’21 winter from that same survey 5.

Bee Informed Partnership 2021 winter colony losses (preliminary data)

This was a sizeable survey involving over 3,300 beekeepers managing 192,000 colonies (~7% of the total hives in the USA).

If hive covers reduce losses to just 5% why does Illinois report winter losses of 47%? 6

Are the losses in this manuscript suspiciously low?

Or, does nobody use hive covers?

I don’t know the answers to these questions, but I also wasn’t sure when I started reading the paper what the authors meant by a hive ‘cover’ … which is what I’ll discuss next.

Hive covers

The hives used in this study were wooden Langstroths and the hive covers were 4 mm black corrugated polypropylene sleeves.

This is what I call Correx … one of my favourite materials for beekeeping DIY.

These hive covers are available commercially in the USA (and may be here, I’ve not looked). At $33 each (Yikes) they’re not cheap, but how much is a colony worth?

Significantly more than $33.

I’ve not bothered to make the conversion of Langstroth Deep dimensions (always quoted in inches 🙁 ) to metric and then compared the area of Correx to the current sheet price of ~£13 … but I suspect there are savings to be made by the interested DIYer 7.

However, knowing (and loving) Correx, what strikes me is that it seems unlikely to provide much insulation. At only 4 mm thick and enclosing an even thinner air gap, it’s not the first thing I’d think of to reduce heat loss 8.

4 mm Correx sheet

Thermal resistance is the (or a) measure of the insulating properties of materials. It’s measured in the instantly forgettable units of square metre kelvin per watt m2.K/W.

I couldn’t find a figure for 4 mm Correx, but I did manage to find some numbers for air.

A 5 mm air gap – greater than separates the inner and outer walls of a 4 mm Correx hive cover – has a thermal resistance of 0.11 m2.K/W.

Kingspan

It’s not possible to directly compare this with anything meaningful, but there is data available for larger ‘thicknesses’ of air, and other forms of insulation.

An air gap of 100 mm has a thermal resistance of about 0.17 m2.K/W. For comparison, the same thickness of Kingspan (blown phenolic foam wall insulation, available from almost any building site skip) has a thermal resistance of 5, almost 30 times greater.

And, it turns out, St. Clair and colleagues also added a foam insulation board on top of the hive crownboard (or ‘inner cover’ as they call it in the USA). This board was 3.8 cm thick and has somewhat lower thermal resistance than the Kingspan I discussed above.

It might provide less insulation than Kingspan, but it’s a whole lot better than Correx.

This additional insulation is only briefly mentioned in the Materials and Methods and barely gets another mention in the paper.

A pity, as I suspect it’s very important.

Perspex crownboard with integrated 50 mm Kingspan insulation

I’m very familiar with Kingspan insulation for hives. All my colonies have a 5 cm thick block present all year – either placed over the crownboard, built into the crownboard or integrated into the hive roof.

Two variables … and woodpeckers

Unfortunately, St. Clair and colleagues didn’t compare the weight loss and survival of hives ‘covered’ by either wrapping them in Correx or having an insulated roof.

It’s therefore not possible to determine which of these two forms of protection is most beneficial for the hive.

For reasons described above I think the Correx sleeve is unlikely to provide much direct thermal insulation.

However, that doesn’t mean it’s not beneficial.

At the start of this post I explained that Andrew Abrahams wraps his hives for the winter. He appears to use something like black DPM (damp proof membrane).

Hive wrapped in black DPM (to prevent woodpecker damage)

Andrew uses it to keep the rain off the hives … I’ve used exactly the same stuff to prevent woodpecker damage to hives during the winter.

It’s only green woodpeckers (Picus viridis) that damage hives. It’s a learned activity; not all green woodpeckers appear to know that beehives are full of protein-rich goodies in the depths of winter. If they can’t grip on the side of the hive they can’t chisel their way in.

When I lived in the Midlands the hives always needed winter woodpecker protection, but the Fife Yaffles 9 don’t appear to attack hives.

Here on the west coast, and on Colonsay, there are no green woodpeckers … and I know nothing about the hive-eating woodpeckers of Illinois.

So, let’s forget the woodpeckers and return to other benefits that might arise from wrapping the hive in some form of black sheeting during the winter.

Solar gain and tar paper

Solar gain is the increase in thermal energy (or temperature as people other than physicists with freakishly large foreheads call it) of something – like a bee hive – as it absorbs solar radiation.

On sunny days a black DPM-wrapped hive (or one sleeved in a $33 Correx/Coroplast hive ‘cover’) will benefit from solar gain. The black surface will warm up and some of that heat should transfer to the hive.

And – in the USA at least – there’s a long history of wrapping hives for the winter. If you do an internet search for ‘winterizing hives’ or something similar 10 you’ll find loads of descriptions (and videos) on what this involves.

Rather than use DPM, many of these descriptions use ‘tar paper’ … which, here in the UK, we’d call roofing felt 11.

Roofing felt – at least the stuff I have left over from re-roofing sheds – is pretty beastly stuff to work with. However, perhaps importantly, it has a rough matt finish, so is likely to provide significantly more solar gain than a covering of shiny black DPM.

I haven’t wrapped hives in winter since I moved back to Scotland in 2015. However, the comments by Andrew – who shares the similarly warm and damp Atlantic coastal environment – this recent paper and some reading on solar gain are making me wonder whether I should.

Fortunately, I never throw anything away, so should still have the DPM 😉

Winter losses

Illinois has a temperate climate and the ambient temperature during the study was at or below 0°C for about 11 weeks. However, these sorts of temperatures are readily tolerated by overwintering colonies. It seems unlikely that colonies that perished were killed by the cold.

So what did kill them?

Unfortunately there’s no information on this in the paper by St. Clair and colleagues.

Perhaps the authors are saving this for later … ’slicing and dicing’ the results into MPU’s (minimal publishable units) to eke out the maximum number of papers from their funding 12, but I doubt it.

I suspect they either didn’t check, checked but couldn’t determine the cause, or – most likely – determined the cause(s) but that there was no consistent pattern so making it an inconclusive story.

But … it was probably Varroa and mite-transmitted Deformed wing virus (DWV).

It usually is.

Varroa

There were some oddities in their preparation of the colonies and late-season Varroa treatment.

Prior to ‘winterizing’ colonies they treated them with Apivar (early August) and then equalised the strength of the colonies. This involves shuffling brood frames to ensure all the colonies in the study were of broadly the same strength (remember, strong colonies overwinter better).

A follow-up Varroa check in mid-October showed that mite levels were still at 3.5% (i.e. 10.5 phoretic mites/300 bees) and so all colonies were treated with vaporised oxalic acid (OA).

Sublimox vaporiser

Sublimox vaporiser … phoretic mites don’t stand a chance

In early November, mite levels were down to a more acceptable 0.7%. Colonies received a second OA treatment in early January.

For whatever reason, the Apivar treatment appears to have been ineffective.

When colonies are treated for 6-10 weeks with Apivar (e.g. early August to mid-October) mite levels should be reduced by >90%.

Mite infestation levels of 3.5% suggest to me that the Apivar treatment did not work very well. That being the case, the winter bees being reared through August, September and early October would have been exposed to high mite levels, and so acquired high levels of DWV.

OA treatment in mid-October would kill these remaining mites … but the damage had already been done to thediutinus’ winter bees.

That’s my guess anyway.

An informed guess, but a guess nevertheless, based upon the data in the paper and my understanding of winter bee production, DWV and rational Varroa management.

In support of this conclusion it’s notable that colonies died from about week 8, suggesting they were running out of winter bees due to their reduced longevity.

If I’m right …

It raises the interesting question of why the losses were predominantly (6 vs 1) of the control colonies?

Unfortunately the authors only provide average mite numbers per apiary, and each apiary contained a mix of covered and control hives. However, based upon the error bars on the graph (Supporting Information Fig S1 [PDF] if you’re following this) I’m assuming there wasn’t a marked difference between covered and control hives.

I’ve run out of informed guesses … I don’t know the answer to the question. There’s insufficient data in the paper.

Let’s briefly revisit hive temperatures

Unusually, I’m going to present the same hive temperature graph shown above to save you scrolling back up the page 13.

Ambient (blue), covered (black) and control (dashed) hive temperatures

There was no overall significant difference in hive temperature between the control and covered colonies. However, after the coldest weeks of the winter (7 and 8 i.e. the end of February), hive temperatures started to rise and the covered colonies were consistently marginally warmer. By this time in the season the colonies should be rearing increasing amounts of brood.

I’ve not presented the hive weight changes. These diverged most significantly from week 8. The control colonies used more stores to maintain a similar (actually – as stated above – marginally lower) temperature. As the authors state:

… covered colonies appeared to be able to maintain normal thermoregulatory temperatures, while consuming significantly less stored food, suggesting that hive covers may reduce the energetic cost of nest thermoregulation.

I should add that there was no difference in colony strength (of those that survived) between covered and control colonies; it’s not as though those marginally warmer temperatures from week 9 resulted in greater brood rearing.

Are lower hive temperatures ever beneficial in winter?

Yes.

Varroa management is much easier if colonies experience a broodless period in the winter.

A single oxalic acid treatment during this broodless period should kill 95% of mites – as all are phoretic – leaving the colony in a very good state for the coming season.

If you treat your colonies early enough to protect the winter bees there will inevitably be some residual mite replication in the late season brood, thereby necessitating the midwinter treatment as well.

I’m therefore a big fan of cold winters. The colony is more likely to be broodless at some point.

I was therefore reassured by the similarity in the temperatures of covered and control colonies from weeks 48 until the cold snap at the end of February. Covered hives should still experience a broodless period.

I’m off for a rummage in the back of the shed to find some rolls of DPM for the winter.

I don’t expect it will increase my winter survival rates (which are pretty good) and I’m not going to conduct a controlled experiment to see if it does.

If I can find the DPM I’ll wrap a few hives to protect them from the winter weather. With luck I should be able to rescue an additional frame or two of unused stores in the spring (I often can anyway). I stack this away safely and then use it when I’m making up nucs for queen mating.

I suspect that the insulation over the crownboard provides more benefit than the hive ‘wrap’. As stated before, all my colonies are insulated like this year round as I’m convinced it benefits the colony, reducing condensation over the cluster and keeping valuable warmth from escaping. However, wrapping the hive for solar gain and/or weather protection is also worth considering.


References

Alburaki, M. and Corona, M. (2022) ‘Polyurethane honey bee hives provide better winter insulation than wooden hives’, Journal of Apicultural Research, 61(2), pp. 190–196. Available at: https://doi.org/10.1080/00218839.2021.1999578.

St. Clair, A.L., Beach, N.J. and Dolezal, A.G. (2022) ‘Honey bee hive covers reduce food consumption and colony mortality during overwintering’, PLOS ONE, 17(4), p. e0266219. Available at: https://doi.org/10.1371/journal.pone.0266219.

Footnotes

  1. Enormous and never ending …
  2. In the lab we place bees on an ice block to anaesthetise them before injection.
  3. December to March.
  4. These were double brood 10 frame Langstroths.
  5. Note that these figures are preliminary – the peer-reviewed paper has yet to appear.
  6. To say nothing of Michigan, Utah and Iowa.
  7. Check this video out if you’re interested – the presenter reckons $8 for DIY.
  8. It’s barely the last but one thing I’d think of.
  9. The 18th Century country name for green woodpeckers, echoing the laughing cry of the bird. They’re also called rain-birds, a name that dates back to the mid-16th Century.
  10. Note the Z not S.
  11. Another example of ’two nations divided by a common language’.
  12. Anyone doubting this happens should look at my CV.

     

    That’s a joke BTW.

  13. Don’t say I never do anything for my readers …

46 thoughts on “Winter covers and colony survival

  1. Etienne Tardif

    Another principle that we forget to mention is air leakage from the seams between the boxes and lids. A shell be correx, tar paper or in my case bubble foil wrap tapped to my boxes to ensure top edge is fully sealed reduces the cooling rate (wind chill) and creates a dead air gap. Leakage also adds up to equivalent ventilation (every mm2 of leakage adds up). Breaking box seals late fall when temps are below 10C may increase leakage due to bees more likely to be clustered, less available propolis, harder to use in cold. The higher up the leakage points in the hive the higher the effective leakage (stack effect). Combine wind chill and leakage and you will have very uncomfortable bees. Note: wind chill is not a real temperature, it can’t get colder than ambient. It is a calculated value based on temperature, wind speed and humidity. Weather Networks love because very cold temperatures and bad weather are good for ad revenues.

    Reply
    1. David Post author

      Hello Etienne

      Good points. I’m opening my hives this weekend for the last time until next March (I have to recover the Apivar strips). They will be well stuck together by now and I’m always conscious of breaking the propolis seals. Temperatures are still in the low teens (°C) here so it should be OK.

      I was going to include reference to some of your winter cluster and overwintering studies but the post was already far too long. I will in the future.

      Cheers
      David

      Reply
  2. keith

    I’ve used a product from low – e the last few years *. it protects from worst of the rain, it’s breathable and insulating too. It’s dead easy to work with as its like a silvered foil. I just cut and wrap and slides up easily under roof. I also use a 50mm kingspan topper on top of the crown board all year round.

    Its a reflective reinforced foil, you simply cut to size and wrap the hive. I also staple it to underside of hive roofs and its great on the underside of nuc roofs as well.

    Reply
    1. David Post author

      Hi Keith

      If you’ve got a link send it to me and I’ll edit your comment (as I’m not entirely sure of the stuff you’re referring to).

      Cheers
      David

      Reply
  3. James Gordon

    Sensible analysis of very flawed study (gives you chance to jump on your various hobby horses I guess). I would like to find a good way of maintaining all my bees overwinter. I live in one of the coldest spots in uk. Maybe grasping at straws – but I could sheath them in straw bales. Rather than kingspan I use sheeps wool. For fear of entangling bees I used to have it in plastic bags. But since discovered they don’t entangle themselves in raw wool.

    Reply
    1. David Post author

      Hello James

      My ‘hobby horses’ as you call them are what I consider the most important determinants in successful overwintering. This is what many beginners struggle with. It’s what I’ve done for several years. I think I’ve lost just two or three colonies over the last 4 years – running an average of 20+ colonies per season – all to queen failures (either late supersedure and no mating or the queen becoming a drone layer in the winter).

      A beginner could wrap his/her hive in any amount of insulation, but without proper Varroa management the probability is that the colony is likely to perish, if not this winter then the next.

      The UK isn’t cold in contrast to some of the places that bees are – very successfully – kept. It’s rare to have temperatures below -10°C for very long. Have a look at the Manitoba Beekeeping website – where the bees are often trapped in the hive for 6 months of the year and winter temperatures are at or below -30°C for several weeks. There are some great photos. There are also suggestions for Wintering Methods, including overwintering two-frame nucs in heated cabinets.

      You could also consider a bee shed

      Cheers
      David

      Reply
      1. James Gordon

        My and my bees rely heavily on your teaching. Thank you. I didn’t mean to diminish your hobby horses.
        Where we stay goes below 20 ‘C every couple of years. It is the intermittent damp/warm and cold which worries me. And yes thinking about a Bee shed/shelter. Kind regards James

        Reply
        1. David Post author

          Hello again James

          The bee shed certainly helps even out some of the temperature variation and the damp is no longer an issue. There are some drawbacks – light is a major issue and needs some careful thought, and there are some colony manipulations (e.g. anything involving a top entrance) that are impossible. However, the pros outnumber the cons in my view and my new(ish) shed on the west coast will have bees in it once I get another shed built for all the junk that’s accumulated over the last 18 months 🙁

          Sorry if I sounded short. I know there are many ways to keep bees, but I also know that relatively inexperienced beekeepers mainly struggle with disease management (though they don’t always realise this is why they’re losing colonies). That’s why I keep ‘banging on’ about managing Varroa and DWV. Once a beekeeper can do that successfully, year in year out, they can then experiment on other ways – organic treatments only, no treatment, holistic, biodynamic, beefriendy or whatever – and see if it works for them. The danger is that they try and run before they can walk, lose their bees, lose their enthusiasm and leave beekeeping.

          Cheers
          David

          Reply
    1. David Post author

      Hello Simon

      Yes, I’m aware of the studies did on the thermal conductance of various modelled hives/trees etc. He and I were speakers at a bee meeting a few years ago. I’m not aware of a follow-up to his studies and – since they don’t involve actual bees but instead involve a number of physics calculations – I suspect they’re less accessible to both the general readership of this site … and me.

      One thing to note is the humidity levels in the poly hives and wooden hives quoted in the first paper I cite … they’re the opposite way round to what I would have expected and, if Derek is correct in suggesting that high humidity in temperate regions retards Varroa reproduction, imply that wooden hives might be beneficial.

      Cheers
      David

      Reply
      1. simon kellam

        Yes I agree I think wood is the best material, just with additional insulation. Some of the thin walled hives that are on the market are totally inadequate for our climate here in the UK. I’m an advocate of using cork and I’m sure it’s made a big difference to survival rates. Winter store consumption is notably less too.

        Reply
        1. Neil Munro

          Thanks for the write up David, It is more confirmation re the benefits of insulation. My bees are now all safely tucked up under Evanii Deep Tops and insulation under correx roofs.

          Hi Guys,
          I use wood too, ‘cos thats what ive got…
          my take on insulation on my Nationals is…. expanded cork between the locking bars on the outside, and a dummy frame on the Northish side of the hive in both the 1 1/2 boxes which I use on all hives through the Winter

          Reply
          1. David Post author

            Hi Frazer

            I’d looked at that expanded cork and was concerned that it would get damp and retain water. Perhaps I’m wrong? I guess wine doesn’t leak through the cork …

            Correx roofs 🙂 Very nice. I saw a comment somewhere recently suggesting that Gorilla tape holds Correx together really well. I’m going to have to try some when I next build some.

            Cheers
            David

  4. Alan Baxter

    This corresponds with work done by Derek Mitchell at Leeds University. He has demonstrated that hives do better if insulated and draught proofed all the year round.

    Reply
    1. David Post author

      Hello Alan

      I might be wrong – and I’m more than happy to be corrected if I am – but I don’t think that’s what Derek has shown. Unless there’s a more recent paper than his 2015 one on thermal characteristics of ‘man made’ hives versus natural tree cavities, I think what he showed was that the latter were much better insulated. This probably benefits the bees, but I don’t think it’s been formally demonstrated. I don’t think any of the boxes he used even contained bees. My recollection is that they had little heaters that generated bee-cluster-amounts of heat.

      He had a follow-up paper 2-3 years ago on hive humidity, but I think that was more to do with the beekeeping season and the potential influence on mite reproduction.

      As I say, if Derek has demonstrated that better insulated hives ‘do better’ (by which I presume you mean better survival) than I’d be delighted to know. It’s not a trivial experiment. As shown in the St. Clair et al., study cited above, because of the natural colony-to-colony variation you would need to use a lot of hives to demonstrate a statistically significant improvement. As I outline above, the ‘improvement’ in colony survival seen by St. Clair et al., – a study that used 43 hives in 8 apiaries – is far from convincing as it’s not explained what the colonies perished from.

      Cheers
      David

      Reply
  5. Geoffrey Spry

    Hi David,
    Last year ( 6th year of bee keeping ) I used a moisture-trapping device on all 6 hives.
    A 3″ deep eke with a fine mesh bottom and filled with light weight wood shavings. Crown board and telescoping lid on top. The shavings got quite damp as the winter proceeded.
    I am on the east coast of Vancouver Island, so moderate temperatures compared to other areas of Canada and USA, so I do not wrap the hives. However we get a fair bit of rain and wind so the hives have a windbreak.
    All 6 survived. However, to reinforce what you have been saying, it was the 1st year I have also done a thorough Varroa treatment plan ( Formic acid in August and OA vaporization in December.
    Coincidence? Probably not. Perhaps a combination?

    Reply
    1. David Post author

      Hello Geoffrey

      I think that sort of deep, moisture-absorbing eke is often used by beekeepers with Warre hives. Vince Poulin – a regular reader, who has already commented to this post – uses Warre hives I think. My colonies, most of which have a perspex crownboard, appear to have relatively little condensation other than in the corners (I’ll try and get a photo this winter). I suspect most condenses on the inside of the walls as they are less well insulated than the roof. It either then runs down out of the way (and through the OMF) or is used by the bees during the processing of stores.

      At least, that’s my guess!

      I think your climate is not dissimilar to ours on the west coast of Scotland – warmish winters (Gulf Stream helps us), cool summers and 1.5-2 metres of rain a year. The point Karen makes elsewhere in these comments – the cooling effect of evaporating damp from the hive surface – might well be reduced by an outer wrap.

      And no, probably not a coincidence 😉

      Cheers
      David

      Reply
  6. paul kirk

    Hi David, a very interesting article, thanks for producing it. wrt whether the temperature measurement frame was within the cluster or not – often there’s a corresponding author on academic papers, so it might be possible to find out through that route. Just a thought.

    Reply
    1. David Post author

      Hello Paul

      Yes, there will be … I suspect they don’t know as it’s clear from the paper that the monitoring was remote and they don’t talk about opening the hive. However, it would allow the position in the two brood boxes to be determined.

      Cheers
      David

      Reply
  7. Karen Alexander

    Hi David
    I also put a thick layer of Kingspan in my hive roof. I found that round bbq covers fit over a National hive and are black on the outside and waterproof. A toggle pulls the open end closed just above the hive opening. Although cedar is water resistant, after rain there will be a cooling effect from the evaporation of dampness on the hive body and covering the hive reduces this type of cooling effect. I keep the wraps on until the weather gets hot as the black outer adds solar gain, then turn them inside out as they are silver on the inside and may prevent too much heat in the hive by reflecting the light.
    I tried it for the first time last year and the bees did well and seemed to come on earlier in the spring.

    Reply
    1. David Post author

      Hi Karen

      Thanks for the ‘top tip’. I’ve got one of those BBQ covers on my composting worm bin 🙂 … they’re great*.

      I posted this photo last winter (late January) of the side of a damp (in places) poly hive. You can see where the cluster must be located by the ‘dried’ area on the outside of the hive. This must reflect loss of heat through the sidewall of the poly. This hive had a perspex crownboard so I could confirm the location of the cluster.

      Abelo hive side wall

      Cheers
      David

      • both the covers and the worms 😉
      Reply
  8. Jeremy Quinlan

    Your two diagrams sub-titled Ambient (blue), covered (black) and control (dashed) hive temperatures weren’t visible to me – I’m not sure why.

    Reply
    1. David Post author

      Hi Jeremy

      Looks like a cacheing problem on my server or my CDN. It should now be fixed. Thanks for the ‘heads up’.

      Cheers
      David

      Reply
  9. Adam Bagnall

    Wrapping may not have much of a direct insulation benefit, but would reduce wind chill on a wet hive. A fleece is warm, but wouldn’t be my first choice of outerwear on a wet and windy day…

    Reply
    1. David Post author

      Hi Adam

      Precisely … and there’s no mention of any of those climate details in the paper unfortunately. I did some searching for Illinois weather from the winter they did the study but couldn’t find much in the time I had available. However, it’s worth mentioning that a damp fleece is remarkably warm because of the air it traps. I know because I fell out of my canoe into the loch this March 😉

      The photo above (or elsewhere in these comments – I can’t remember the order they appear) of the side of a poly hive shows there must be quite a bit of heat loss to evaporate off the surface dampness from the hive sidewall. A wrap, presumably also trapping a bit of air inside, should help for the reasons you say.

      Cheers
      David

      Reply
  10. Vincent Poulin

    David – yes, here on the west coast of BC we share a similar wet, cold climate. Many keepers now have gone to what are referred to as “quilts”. They were a Warren thing but now people just size them to hives. They are filled with wood shavings as Geoffrey mentioned and I have in the past. Their purpose is the move moisture out of the hive and they work very well. A 3-4″ layer acts to insulate the hive while allowing water to move up and out. Common is for the upper shavings to become wet but lower ones stay dry. Holes in the sides of the quilt box help to move moisture out. I don’t wrap my hives mostly because the walls are made of waste housing framing material. I think here winter temperatures are the least of our problems. Varroa is the killer. They are incredibly pervasive and thrive in our environment. Clearly the number 1 challenge for BC bee keepers. That said quilts are great. Most years bees cluster right below my quilts.

    Reply
    1. David Post author

      Very interesting Vince … the clustered bees in my hives often form a wide thin cluster rather than the conventional rugby ball (oval) -shaped cluster. I think they’re all trying to get into the warmest part of the hive. You only see them like this when it’s very cold.

      All of this talk of hive temperatures is making me wonder whether I should revisit my homemade hive monitors. Too late for this winter, but I could probably get everything working properly for next year. The monitoring is relatively trivial … it’s getting the probes in the right place that’s a challenge. By then I might be able to make the comparisons between bees in a shed and outside. Etienne Tardif – who has commented elsewhere in this thread – has done a lot of work on winter hive monitoring and is a regular contributor to the Bee-L discussion forum.

      Cheers
      David

      Reply
  11. Juhani Lundén

    We have 5-6 months winters here in Finland. Temperatures might be around -30 C for several weeks in December, January,February or March. Normally however around +5 and -20 C. My bees overwinter since year late 1990s in 18 mm plywood boxes and tar paper around. Bees remove food from the outermost frames and create natural insulation on the sides. On top of frames I have waterprood greenhouse plastic, and a 5 cm polyurethan sheet for a roof /outer cover.

    I am not totally convinced about the benefits of tarpaper, I have done without some winters, but the 5 cm insulation on top is a must.

    Bees must sit cold in winter to ensure they move and consume as little as possible. Moisture must be removed. These are the facts why I double my entrance for winter. 2x 44 cm entrance front and rear. Queen excluder for mice underneath.
    The air flow underneath is also used in Swedish/Finnish polystyren hive structures, like Nacka, Paradise Honey and HoneyPaw: they have a mesh in the hive bottom. This might expalin lower moisture in the reseach results, too.

    And my bees have been without treatments since 2008…

    naturebees.wordpress.com

    Reply
    1. David Post author

      Hello Juhani

      I took the liberty of converting the web address into a hyperlink … more chance visitors will click on it.

      I don’t think there were differences in the floor on any of the hives described in the post above. At least, the authors son’t mention it and it would be yet another variable to confound things. All my hives have open mesh floors and I too think it’s very important to avoid damp in the hive overwinter.

      Interesting how the bees remove stores from the outside …

      Cheers
      David

      Reply
  12. Jacob Self

    This is a fantastic article and topic. I am in the US and it’s difficult to find Poly products, everyone uses wood. Please do more like this.

    Reply
    1. David Post author

      Hello Jacob

      Pleased you enjoyed it. It’s odd, I don’t think either Mann Lake or Dadant do poly hives. Blue Sky Bee Supplies sell the Paradise ones. These are nicely made but have that dreaded ‘lip’ or rebate meaning the boxes aren’t compatible with wooden boxes (or almost anything you have in the apiary). I’ve got some of the older style Paradise boxes and these days only use them as bait hives (or swarm traps as you probably call them). I’m sure there are other suppliers as well, that was just a very quick search.

      About 50% of my boxes are poly these days. The good ones last well, are tough, almost totally weatherproof and the bees do well in them. Although some comment on the environmental damage they should last 3-4 decades. Painting them with an exterior oil based paint really helps them stay looking good.

      Cheers
      David

      Reply
      1. Iain Dewar

        Hi David, very interesting article.
        My own hives have a bit of age to them (I’ve never bought a brand new hive!), and they have all seen plenty action one way or another so they don’t fit together perfectly without the odd small gaps. The bees quickly seal these up after every inspection during the season when the temperatures are well up, and their clear message there is that they don’t like draughts even in summer. I make final full inspections fairly late on just before preparing them for winter and am aware that they don’t, or rather they can’t propolise any leaky joints at this point in the season so I simply duck tape all the box joints during final winter prep. The tape is removed at first spring inspections. Winter draughts in the hive are deadly, taping works well along with not positioning hives in exposed positions.
        With my engineers head on, using a matt black covering on the hive will certainly absorb heat from the sun, it will also quickly cool it down in the breeze or cold conditions. Think motor car radiators!
        Beyond health, colony strength and winter stores, keeping colonies draught proof is an important key to winter survival.
        Cheers
        Iain

        Reply
        1. David Post author

          Hi Iain

          When I was writing about black wrapping hives I was thinking back to ‘good absorbers and good emitters’ from my O level physics (but, because of my woeful O level physics decided the less said about it the better as I was probably wrong 😉 ). Thanks for bringing it up. Perhaps some experiments are needed? It’s a regular practice in the US and I’d hope/assume that someone had determined it was the right thing to do through practical experience.

          I completely agree with your comments about draughts. They clearly ‘dislike’ gaps above or to the side of the brood nest (though they do nothing about the OMF). Here’s a photo of an Abelo crownboard with the vents completely filled in with propolis.

          Abelo crownboard

          My boxes were opened for the last time this weekend (to remove the Apivar strips) and I can administer OA without doing anything but blocking the entrance, so they shouldn’t be disturbed until at least March. It’s still relatively warm so I’d hope they’d get a chance to glue the crownboard back before the temperatures drop.

          Cheers
          David

          Reply
  13. Steph Curtis

    Hi David
    I’ve really enjoyed reading your posts, to add to / compare to my other sources. I live high in the Peak District and have had a fantastic first year of bee keeping so far. Starting with one colony I now am proud to manage two colonies, a huge harvest of surprise heather honey. Both treated for varroa, fed and both feeling good and heavy. Both colonies are in Abelo hives. The reason for my post, is that I think you have some of your bees in Abelo hives. My question is, do you manage to get some kingspan under the roof to add some more insulation, could I put a block of kingspan on top of the hive? Or in your experience is this not necessary? I don’t think there is room to put some under the roof, and Abelo don’t sell an eek… I just wondered what you do?
    Best wishes
    Steph

    Reply
    1. David Post author

      Hello Steph

      I’ve got several Abelo hives. Mine have a deep roof (they are about 5 years old by now – probably the model before this one from their current catalogue) and so can easily accommodate a 50 mm thick block of Kingspan. Perhaps your hives are the newer style that they sell (like this).

      I don’t know how thick the current roofs are but I do know that you can usually see where the cluster is located on a frosty day through the sidewall of the hive by looking for the ‘dried’ area where heat from the cluster has evaporated the damp from the hive surface. I posted a picture of this somewhere else in these comments. That being the case it shows that the sidewalls – and I expect the roof – could be better insulated, though accepting that they are already better than cedar.

      One option is to build an eke (not eek … that’s what people say when they see a mouse 😉 ) 50 mm deep and then fill the space with insulation. Alternatively you could cut a block of insulation to fit inside a poly super and place this on top of the crownboard. Whichever you choose (and I’m sure there are other ways) make sure the insulation is flush against the crownboard. You want to avoid any cold air spaces.

      Pleased you enjoyed your first year … for most of the UK is was a great season (they’re not all like this!).

      Cheers
      David

      Reply
      1. Steph Curtis

        Thanks for your time, I’ll enjoy fixing up a solution one way or another!
        and I’ll check my spelling!!
        😂

        Reply
        1. David Post author

          Hi Steph

          I now notice that my reply contains a typo! Enjoy finding a solution. One of the recent comments I’m about to respond to describes a Kingspan cover for the entire hive … another possible approach.

          Cheers
          David

          Reply
  14. Mark Haworth

    I wrap and hotbox/quilt my hives upstate NY (average lows for sustained periods of -10C) and have max 5% losses year after year. (Of course I treat for varroa too!)
    I was always told that the reason to wrap/insulate was far less to do with keeping the hive a bit warmer or less draughty and WAY more to do with helping maintain a more constant temperature, whatever that temp may be. That way the cluster isn’t constantly opening up and reforming and wasting more resources.

    That might mesh well with Juhani’s comment that “Bees must sit cold in winter to ensure they move and consume as little as possible”.

    As a complete aside, given questions from US readers about insulation, poly hives are readily available from a national distributor called BetterBee. I used to use them but found wasps/yellowjackets over time work out how to eat right through to to the inside. A far cheaper way to insulate is to buy industrial double layered polyethylene industrialized air bubbles (such as Poly-Air) which are bonded between two layers of highly reflective metalized aluminum polyester film. You can insulate a hive for $10 with this and it lasts for many years and is easy to store.

    NOTE : Hi – I’m absolutely not looking for this to be published, but the slightly convoluted description of the insulation was to make it easy for someone to google.
    It’s just this – https://www.amazon.com/dp/B07G66G3Y9?psc=1&ref=ppx_yo2ov_dt_b_product_details
    which the manufacturer will also happily sell direct for a lot less.
    Just in case anyone asks!

    Didn’t want anyone to think I had some product placement deal 🙂 It’s really just rafter insulation but works incredibly well.

    Reply
    1. David Post author

      Hello Mark

      I took the liberty of linking to BetterBee …

      I’ve got several different types of poly hives. The Abelo ones I’ve found to wasp-resistant, but some of my older Swienty ones are made from a softer material and I’ve had wasps burrow in (or out) to get to honey stores.

      I also amended your post by inclusion of your follow up with the link to the insulation you use. I’ve gone out of my way to keep advertising and product placements off the site, but am happy to include recommendations from end-users who have a solution that they know works (particularly if it only costs 10 bucks 😉 ).

      Cheers
      David

      PS In the UK there’s ample choice of similar insulation to that mentioned above – here for example.

      Reply
  15. Jesper Petersen

    Hi David,
    I’m based in West Lothian, Scotland, UK. My apiary is 125m above sea-level and the wind can get a bit feisty at times.
    I am now going into my second winter using 4mm black Correx to wrap around my hives (made from 8’x4′ sheets from eBay). The sleeves are put together with duct tape, which so far seems to be holding up against the elements. They are a bit of a tight fit around my BS National hives but fits inside the roof with a bit of persuasion which helps to secure them in place. Under the roof is an eke with 50mm Kingspan insulation. The floor is open mesh and is the only ventilation.

    Reply
    1. David Post author

      Hello Jesper

      You’ve done well holding Correx together with duct tape. I found the make I used (and I’m sure they differ) dissolved within a few months. The stuff I use – recommended on the page where I describe making things from Correx – is very waterproof and last years outdoors.

      Happy wintering … roll on spring 🙂

      Cheers
      David

      Reply
  16. Paul

    Hi David
    I’ve read your posts for some years always with great interest and thank you for your efforts. I’ve keep bees in Aberdeenshire for 40years and like you DIY my way to solutions beekeeping problems. My experience of wintering (and summering) bees here is in tune with other contributions here. I ‘wrap’ all my wood boxes in 40mm kingspan equivalent on all 4 sides, use black polythene for a crown board (bees propalise it to the box successfully), 40 mm kingspan over this, no roof, but instead a sheet of approx. 24”square correx (also a fan) (maximising use of 8×4 correx sheet) or better still similar size cut from aluminium sheet recovered from a caravan!…topped by a brick or 3 to hold all down. This ensures all underneath remains dry. I think that the latent heat lost from wood walls in our eastern never mind your western winter climate is significant and probably is also a factor even with poly boxes as evidenced by your pics of the position of winter clusters in the poly boxes. I suspect benefits the wrapping of colonies will be at least in part down to latent heat savings especially during damp post frost spring brood rearing.

    Reply
    1. David Post author

      Hello Paul

      Sounds like an interesting solution to the varied weather that makes Scotland such a great place to live (and that’s not sarcasm … it would be dull if it was the same all the time). If you have a photo I’ll add it to your comment – just email me it using the link at the bottom of the page. Anything that helps the bees build up in spring is a bonus.

      Have a good winter.
      Cheers
      David

      Reply

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