We have had a few 'life' things come up in the last month or so with MrT working away and me coming down with every bug that is floating around at the moment (thank goodness for honey for soothing the throat!) So we have been a little tardy with settling our hives down for the winter. I say winter, but I really mean: the time in WA when it is a bitterly cold for a month or so and it rains for a couple of days ;-)
The first winter we had with our bees, I freaked out about how much honey to leave the ladies with. Everything I read online was pretty much applicable only to places that have a real winter, so we ended up leaving lots of honey for them. It wasn't a problem, we just harvested what they left in the spring. But balancing what honey they will need for food, with the space that they will consequently need to keep warm over winter is a little tricky. Now after a couple of seasons, we are becoming more confident about gauging the strength of the hive and using long term forecasting of the weather for a guide. We tend to err on the side of slightly too much honey stores - mainly so that we don't have to supplement stores with sugar. Our bees tend to maintain the stores, since they can fly during the winter about 2 days out of every 4 - 5 days. When it is cold, windy or wet the bees don't tend to fly, so production grinds to a halt. Our observations have found that there is a very limited amount of food in the flowers (after rain washes out pollen and nectar) but because of our delightful winter sunny days between the big rain fronts, the bees can replenish a small amount of honey over the winter.
Here is a thermal image of a hive during winter. The bees cluster within the hive, around the Queen and brood, and spend time each day on the outside of the cluster, similar to penguins in Antarctica, before folding back into the cluster for food and warmth. Bees take turns inside the empty cells of comb to keep the brood warm so they can develop properly. They detach their wings from the socket and inside the cell they 'beat' their wings which causes vibration within their bodies that raise their body temps. This heat radiates from the bee to the brood in other cells. They can keep up to 8 other cells warm by raising their body temperatures to approx 44 degrees. This is about 9 degrees higher than their usual body temperature. Scientists are still baffled as to how they acheive this heat increase without cooking their brains!
From this picture, you can see the 'random' cells left empty. This is actually good planning from the bees to allow 'bee warmers' in to do their jobs! After looking at my hives in the yard and thinking (a little guiltily) how I need to do an inspection before the winter really sets in, I thought you all might like to see what other keepers do where they have a real winter.
UK: silver waterproof lining and hessian blankets. These keepers are very conscious of damp, which is worse for bees than cold temperatures, and have been careful to provide good ventilation.
(Photo: http://www.rosybee.com/blog/2010/12/beehives-in-winter, http://www.telegraph.co.uk/gardening/beekeeping/7740088/Readers-hives.html?image=1)
Northern US: These hives have slightly tapers tops for snow to drop off, and using a material lining, with black plastic over the top. The black absorbs whatever sun is out to add a little more heat inside the hive. In cold climates that don't have as much rain, ventilation area can be slightly smaller. The hives under all that snow would have the same...I think!
Here in Perth it is the heat that we worry about. The bees struggle with carting enough water to keep the brood cool. But that is a story for another day!