Convenience or laziness?

It’s cold and dark and all is quiet in the apiary. Hives appear somnolent. Colonies are clustered 1 and, other than the odd corpse or two on the landing board, I’ve not seen a bee for at least a fortnight.

The apiary in winter ...

The apiary in winter …

Based upon previous experience I suspect colonies are – or very soon will be – broodless. I usually reckon that the first extended (2-3 weeks) period of cold weather 2 in the winter is the most likely time for the colony to be broodless.

In 2016/17 this was the first week in December.

In 2017/18 it was just a day or two later.

In both instances, when the hives were checked, they had no brood.

What’s all this about being broodless?

If a colony is broodless there are no capped cells in which the Varroa mite can ‘hide’. As a consequence it’s an ideal time to apply a miticide like a trickled solution of Api-Bioxal 3.

There are very good reasons why a midwinter OA treatment is necessary, particularly if you treated early enough in the autumn to protect the overwintering workers from the ravages of Deformed Wing Virus (DWV). High DWV levels reduce the lifespan of bees and contribute to many (possibly most) winter colony losses. I’ve even suggested here that “isolation starvation” might actually be due to Varroa-transmitted viral disease.

Time of treatment and mite numbers

Time of treatment and mite numbers

Early autumn treatment protects the winter bees but also leaves the long autumn for the residual mites to continue replicating.

And there will be residual mites. No treatment is 100% effective.

So, paradoxically, if you treated early enough in the autumn to really help protect the winter bees, your mite levels will be higher at the end of the year.

Which also means they’ll be higher at the beginning of next year.

Not a good start to the 2019 season 🙁

Convenience or laziness?

Many beekeepers, for convenience, laziness or historical precedent, choose to apply the winter OA treatment between Christmas and New Year. I suspect that this is often too late. If the queen starts laying again around the winter solstice there will be sealed brood – and therefore unreachable Varroa – by the end of the month.

I’d prefer to have a cold and damp afternoon in the apiary slaughtering Varroa now than the convenience of treating them less effectively during the Christmas holiday period.

The latter might be more convenient … the office will be closed, I’ll be replete with turkey and sprouts and it will be a good excuse to ‘escape’ visiting relatives and yet more mince pies 4.

But is it the best time for your bees?

We have the technology

We have a couple of hives with Arnia hive monitors fitted 5. These have a temperature probe inserted into the brood nest. Brood rearing temperature is around 34°C. Here is a trace of one colony over the last month.

Arnia hive monitor temperature

Arnia hive monitor temperature

The colony temperature was pretty stable (around 33-35°C) until about the 19th of November and has dropped about 10°C since then. Although I’ve not opened the colony I think that this is additional evidence that the colony is broodless 6.

Beekeeping by numbers

Keeping bees properly involves being aware of the seasons, the available forage and the state of the colony. This varies from month to month and year to year 7.

You can’t mechanically (‘by the numbers’) add supers on the 5th of May and harvest honey on the 15th of June. Sure, it might work some years, but is it the best time to do it?

Similarly, you can’t optimally treat a colony for Varroa on the 30th of December unless the climatic conditions and state of the colony coincide to make that the best time to treat.

It might be, but I suspect that generally it’s a bit late if there is a brood break.

If you’re going to the trouble of preparing the OA treatment, donning the beesuit and disturbing the colony you might as well do it at the right time for the bees.

I’ll be treating in between the predicted sleet showers and sunny periods this weekend.

Time to treat

Time to treat

Isn’t evolution a wonderful thing? This post started with a working title of Know your enemy” and was on a different topic altogether. I’ll save that for next week.


The above was written at the beginning of the week. Now the weekend is closer it’s clear the weather is going to be cold with heavy snow predicted. Unless the forecast is wrong (and how often does that happen?!) I’ll hold off treating until a) it’s over 5°C, and b) the roads are safe.


  1. Standard geographic disclaimer applies here … my apiaries are in Fife, Scotland, where the average monthly temperature is currently around 4°C.
  2. Which we’re in now.
  3. Other oxalic acid (OA)-containing treatments are available, so to generalise I’ll use the term OA treatment.
  4. Some artistic licence here … I’m not keen on mince pies, there’s nothing I like more than visits from relatives, I never eat turkey at Christmas and I’ll be in the office anyway. Or was that artistic licence?
  5. More on these next year. We’re still getting used to the technology.
  6. Of course, the colony may have moved away from the probe. This is unlikely. It’s a very strong colony in a cedar brood box in our bee shed. The current temperature (~22°C) is still much higher than ambient. This indicates that the probe remains within the cluster. I’m therefore reasonably confident they’re not rearing brood.
  7. And at times from week to week and even day to day.

25 thoughts on “Convenience or laziness?

  1. Dave Stokes

    A welcome and timely reminder of the mechanics of varroa treatment but I wonder just how many of your readers will take notice.

    1. David Post author

      Who knows? Clearly those who find it inconvenient or who can’t be bothered probably won’t … but I don’t expect them to be reading this anyway. The ‘beekeepers’ who bought a nuc in early summer, dumped it into a hive and checked it in mid-September expecting kilograms of lovely honey also probably won’t be reading it, so won’t take any notice. They’re also unlikely to have any bees in Spring.

      Keeping bees well isn’t rocket science, but it does take effort. There are too many beekeepers who don’t properly appreciate the principles and practice involved.

      All I can do is write the stuff. I know from discussions with engaged beekeepers at evening presentations that at least some ‘get the message’.

      That’s a start …

  2. Karen Alexander

    I’ve been hoping you might mention your OA treatment. I remembered that last year you treated in December, whereas it was Janbefore I felt able to. Here in Devon it’s a bit warmer and there’s been no prolonged cold spell yet, just a few days in a row. I agree it’s about trying to gauge the weather and be mindful of the bees behaviour. For me I’m still holding out on my treatment but wondering whether to bite the bullet and have a sneak peek at the brood. I have a camera on a long cable like an endoscope and thought that might give me some clue about brood.

    1. David Post author

      Hi Karen
      I’m not sure the endoscope camera is a good idea (though haven’t used one, so this is just a guess). The bees tend to be reasonably tightly packed so the view might be restricted. If you view the cluster from the top it’s easy enough to find the middle two frames. Split them there (you’ll have to remove one of the outside frames first) and quickly lift one out and look at the exposed face. If there’s brood in the colony, that’s where it will be. It takes 10 seconds and isn’t too intrusive.

      PS I should add that pulling out Apivar strips – sort of the reverse of inserting an endoscope-type camera – tends to roll the bees a bit and is sometimes resented.

  3. walrus

    That brood temperature chart is a real eye opener – I have often seen little sealed brood in late Aug/early Sept in my hives but have never had a way to know whats going on in the hive in Nov/Dec. I’m about to zap them with Oxalic Acid (sublimox) this weekend. My guess is that my bees in Cheshire follow a similar pattern to yours but possibly deferred by a week or two because it’s normally a bit warmer here.

    1. David Post author

      I’m going to discuss the Arnia stuff when I have some more experience with it. It’s the first winter with it. The winter broodless period wasn’t the reason we got it, but – hey – if it helps now as well then I’m not complaining 🙂

  4. David Maclean

    Being fairly new (second winter) I do worry about treating v temperature. I intend to vaporise from below the varoa mesh and worry that a treatment may disturb the cluster – so if very cold they may have more fatalities than leaving it to a warmer period. I note you say that you would not treat if below 5 degrees, I assume this would be the same for vaporisation?

    1. David Post author

      Frankly I don’t think the treatment temperature is too critical. Given the choice I’d probably sublimate when the temperature is a bit higher. The cluster will be a bit more open and the vapour will therefore penetrate better. I’ve trickled OA loads of times between 0 and 5C with no apparent ill effects. The ‘Stop Press’ comment refers to sublimation. There’s a very hard frost this morning and the warmest part of the day (2-3C) is predicted to be when the snow is supposed to be heaviest.

      I care for my bees and I want them to have the lowest mite levels possible … but I’m not going to risk dodgy road conditions or fight through snowdrifts to treat today. They’ll be fine until midweek when the temperature will be a bit higher.


  5. Sean

    Hi David,
    When I use OA, I vaporise it from below the floor and I let it flow up through the mesh floor.I have noticed that the bees don’t like it and often climb out of the hive and cling to the outside even when cold, the following day there are sometimes corpses clinging to the hive.

    Do you ever see this behaviour.This doesn’t feel normal, and I wonder if I am overdosing them


    1. David Post author

      Hello Sean
      It isn’t normal, but then neither is squirting OA vapour through the hive … as far as the bees are concerned. Inevitably the colony is disturbed a small amount when sublimating. I usually administer the treatment through a small hole in the rim of the floor, having sealed the entrance. I then leave the entrance sealed for a few minutes after treatment to let the OA settle onto all the surfaces inside the box. Under these conditions I very rarely get bees leaving the hive. If you look through a perspex crownboard you can see the bees getting agitated as the vapour spreads … but they soon settle down again. However, the few boxes I have to treat via the front entrance (generally nucs or those with the Abelo floors) do usually end up with a few disorientated bees flying/crawling out. Some are liberally coated in OA and some return to the hive. Don’t worry about this.
      It’s difficult to overdose with vaporised OA. Studies have been done on this. Unless you’re repeatedly administering panfuls of the stuff you’ll be well within the limits. I use 1.6g as that’s what my scoop weighs out … obviously with the additional ingredients they’ve added to Api-Bioxal this means that the amount of OA is actually only about 1.5g.
      Also don’t worry about losing a few bees midwinter. It happens all the time. Think about the colony size at the end of the summer and the size in midwinter. There’s probably a reduction in numbers of at least 15,000 bees … over perhaps 4 months or so. This equates to 125 bees a day. The few you lose when treating is insignificant (unless it’s the Q!) and the benefits in terms of colony health far outweigh the losses incurred.
      Seal the hive and leave it sealed for 5 minutes after treatment. They settle down pretty quickly.

  6. Emily

    Snow! Good luck and stay warm. It feels a long way from us down in Cornwall but the amount of rain here is making me nervous.

  7. Gary Thomas

    Having read your posts on winter varroa treatments using Oxalic acid I’ve bought some acid and a trickle bottle (form Thornes) and carefully read all your posts about the mix to use and the safety procedures to follow. And to answer Dave Stokes’ question – at least one of us!

    I have just one hive and a poly nuc to treat in my back-garden apiary. You mention that the time to treat is after 2-3 weeks of cold weather; I’m wondering what constitutes ‘cold’? Is is below 10C, 5C or colder?

    Here in the Midlands (Banbury, to be precise) it’s currently about 0-1C but next week getting up to 8-10C so I’m not sure if it’s the right time to treat or not. All help / advice appreciated.

    1. David Post author

      Hello Gary
      You have to use your judgement as there’s no hard and fast rules I’m afraid. The colony clusters below about 7C. As a first approximation I’d be looking at a fortnight with temperatures lower than that. It might not have occurred yet, and might not at all. However, I kept bees in the Midlands for about 6 years and there was usually a winter brood break. You can check for brood and if done carefully and quickly you won’t harm the colony. The LASI group in Sussex (warmer than where you are) have even recommended forking out brood when treating to ensure the colony is broodless. I’ve not done that and don’t need to because I’m pretty confident I’ll be able to identify a broodless period.
      Finally, remember that – even with limited brood present – treating is likely to be beneficial if there are significant numbers of phoretic mites.. You won’t harm the colony, but you might not get the very best result in terms of the proportion of mites slaughtered.

      1. Gary Thomas


        Thanks – as a new beekeeper I’m (slowly) getting used to the idea that ‘there are no hard and fast rules’!

  8. John weightman

    I had a try with the glycerine oxalic mix, using paper towels and cardboard as the carrier, put on in August after clearing the supers. There was so much wildlife on the varroa boards when I checked them some weeks later it’s hard to tell what the drop was. Treated with OA 2 weeks ago and today’s total counts for those weeks is barely into double figures. Most of the carrier had been removed, I treat through top. I guess I won’t know for sure till spring.
    Always interesting notes thanks for your efforts

    1. David Post author

      Interesting … I’ve read details of this on Randy Oliver’s ScientificBeekeeping. I see the potential benefit of slow release, but it seemed that he was still working on the best ‘formula’. Multiple vaporisations in early autumn is certainly more work than the glycerine/OA mix … or just dropping an Apivar strip in.
      As I’d feared, it was too cold today to get the car out of the drive, so I’ll hold off treating until Wednesday when it’s predicted to be a little warmer and drier. Spent the day melting out old brood frames instead.

  9. calum

    I am treating 21 days after the first frosty nights here in Germany (funnily enough that will be somewhere between Christmas and New Year). So all the brrod the colony had has hatched out.
    In the past I have had colonies that were certainly with brood as I have done the OS treatment. But I never lost a colony that was alive at Christmas.

    Somewhere I read (or heard in a seminar-I forget) that Varroa does not tend to go into the brood immediately when it is available (otherwise it would all rush onto a few cells and probably not be viable). – I guess that is due to a small brood patch not being aluring enough to pull them of the bees. So I dont worry myself about small brood patches, so long as I get the other 90% I know they will be fine. If not the issue was more likely with my autunm treatment than brood levels during my OS treatment.

    1. David Post author

      Hi Calum
      I’ve also often treated when there’s brood present when I lived in a warmer area. However, in most winters there is a broodless period and – if you can treat to coincide – it will definitely be beneficial.

      The point you make about colonies with lots of mites and the queen just gearing up and laying again is a good one, and something I’ve talked with my friendly Varroa experts about. If all the mites dived into the new brood as soon as there was any (after a broodless period) they’d be heavily infested and surely doomed. As you say, they might not be viable and might not even emerge, so entombing the new mites (just as A. cerana does).

      Alternatively, perhaps infestation at low temperatures, low brood availability, low nurse bee levels (or who knows what?) is significantly slowed … for example, the phoretic mite might (too many mites!) only enter a cell at 10% of the rate it would in high summer with limitless brood. This would slow things down and let the colony expand until it could ‘cope’ with infestation better. Or perhaps mite maturation – something I’m going to discuss soonish – is very much slower, with an average of weeks, rather than days. Or perhaps there’s a high attrition rate in terms of mite viability over the winter, as they get older perhaps they get less good at entering a cell.

      Someone probably knows the answer to this, but – at the moment – it isn’t me I’m afraid. I’ll ask around.


      1. Calum

        Hey David!
        maybe there is a “hunger” pheromone threshold that needs to bee reached before the varroa make the life or death “jump”.
        Similar to the pheromones from drones attracting more mites?


        1. David Post author

          Could be … though surely they’d be hungry after a long broodless period and so should ‘grab’ the first available larva of a suitable age? Of course, if the metabolism of the mite is is slower in the winter (an assumption) perhaps the levels of the hunger pheromone are reduced, or build up less strongly.

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