Causes of Winter Losses

Wintered hives in Calgary, February 2018.    (Credit: Mark Soehner)

Spring teased us today. It looked good for a few minutes. The sun was shining and we could imagine that someday it could be Cancun-warm here. But we will get another layer of snow tonight here in western Canada. Nevertheless, people are starting to peak at their bees. A neighbourhood beekeeper sent the lovely photo, above, which he took a few days ago. Mark said his bees are looking good – both hives are alive – and he starting feeding them some pollen substitute. The snow, by the way, provides great insulation and the exposed hive-fronts are facing south.

March is often the worst for wintered bees in our climate. Old over-wintering workers shuffle off to their last snow pile and the weakened hives sometimes suffer greatly from the stress of fluctuating temperatures, low stores, and small clusters. The queen will do her best, but her brood needs warmth and food.

With that in mind, I thought that I’d share the list of common beekeeper excuses for dead hives. These data were gathered from beekeepers by CAPA, the Canadian professional apiculturists’ association. Bees in your area may succumb to other winter maladies, but here’s what Canadian beekeepers self-reported last spring:

Poor queens topped the list as the number one reason for winter losses in most provinces. However, in Alberta, Canada’s main beekeeping province, beekeepers say most hives were lost because of “ineffective varroa control”.  Now, that’s a real problem if it means that mites are out-witting the dope we use to kill them.

Weak fall hives was cited as the main culprit in Manitoba and the second leading cause of winter loss in four other provinces. This could be due to mites weakening the hives in autumn or it could be because brood nests plugged out in August, leaving no open areas for the queen to lay. We almost had this problem a decade ago in our own operation. We ran around sticking empty frames into the brood nests in early September. That saved our bees, but many operators were caught off-guard – Alberta had high winter losses that year.

Starvation was the third most common explanation for losses over 2016-2017.  This may happen if bees build up too fast in February and beekeepers can’t get into remote snow-filled apiaries. Starvation might also happen in weak colonies that can’t generate enough heat to move their cluster to nearby honey combs. That’s always sad for the beekeeper to discover – ten pounds of honey inches away from a dead mass of starved bees.

Quite a few beekeepers simply said that their bees were killed by “weather”. I’m not sure what that’s supposed to mean. Too cold? Wrap the hives and keep stronger wintering colonies. Too windy? Shelter them. Too long a winter? Well, that’s a killer for all of us and I don’t have an easy answer.

Winter losses for Canada were around 25% last year. That’s an awfully high loss. In the days before mites and cell phones, losses were around 10%. (Cell phones has nothing to with it, but the days before mobiles were good days.)  I don’t know if we’ll see 90% success in wintering again – we might eventually subdue mites, but ag-chemicals, pollution, and other bee stresses will likely keep losses high. Beekeeping’s not for the faint-hearted.

Winter’s not over yet. Hopefully, Mark’s bees will begin to build nice populations and they won’t suffer during the next two months of unsteady weather. He’s keeping an eye on them and he’s ready to give them any help they’ll need.

About Ron Miksha

Ron Miksha is a bee ecologist working at the University of Calgary. He is also a geophysicist and does a bit of science writing and blogging. Ron has worked as a radio broadcaster, a beekeeper, and Earth scientist. (Ask him about seismic waves.) He's based in Calgary, Alberta, Canada.
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9 Responses to Causes of Winter Losses

  1. Pingback: Causes of Winter Losses | Raising Honey Bees

  2. bryson says:

    3 weeks ago here in mb the sun came out on a -20 degree day and my bees came out for a cleansing flight.most of them only made it 2-3 ft before the -30 wind chill knocked them down into the snow.i probably only lost about a 100 bees.i am wondering if I should have closed off the entrances with a small mesh to hold them in till warmer weather or not to worry about the small loss.


    • Ron Miksha says:

      That’s awfully hard to prepare against. Can you/should you prevent bees from having a cleansing flight when it’s -20? (Have you thought of living in BC?)
      We’ve seen the same thing out here in Alberta with mid-winter chinooks that get the bees flying when they’d be better off sitting inside. We’ve never closed off entrances with bee-tight mesh to prevent that, but lots of commercial beekeepers put hives in dark sheds with no cleansing flights possible for four or five months. And in thee old days, some beekeepers locked their hives into root cellars for months. So, blocking them in might be OK. My guess is that not much damage was done to your bees and those sorts of February forays are probably rare in Manitoba.
      By the way, thanks for the comment because it certainly fits into the ‘weather’ category which I didn’t really answer very well in the blog.


  3. Pingback: Causes of Winter Losses | Beginner Beekeeper

  4. Kendell Killian says:

    I love reading all your work but this weeks article made me wonder if I am the only one wondering about suffocation as a winter lose this week the winds picked up again (southern Alberta winds are common) and two days later all my beehives top entrances are 2 feet below the snow. We have had a lot of snow and drifts this year I dig out the top entrances after the storms but I am very worried this time, I wasn’t able to dig them out until 2 days after they were covered. Is suffocation from snow a thing. I would love to hear more about this.

    Liked by 1 person

    • Ron Miksha says:

      Thanks for the kind word about the blog. Glad that you enjoy reading it.
      You have a good question. A lot of beekeepers worry when hives are buried by snow.
      I don’t think you’ll have a problem. When I kept bees in northern Saskatchewan, hives were sometimes buried in snowbanks from mid-November until late March. They didn’t suffocate, but if they are buried too long, the hives can’t vent moisture which can build up and hurt them. In most of those buried snowbanks back in Saskatchewan, the heat of the stronger hives melted a snow cave under the crust and that’s where bee exhaust went.

      I was surprised to find this about bees’ need for oxygen:

      The insect respiratory system is so efficient that resting insects stop taking in air as they release carbon dioxide, according to research by Stefan K. Hetz of Humboldt University in Berlin, Germany. This allows them to keep oxygen and carbon dioxide levels in balance.

      I wrote more about the bees’ needs for fresh air at an earlier blog posting:


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