November 22nd and a heavy frost, should mean that the wasps have now gone. I am overwintering several smaller nucs of bees as I have done in previous years, but they are always susceptible to wasp stress. All seem ok and are in polynucs which as we will see later offer extra support to the bees especially smaller colonies in the winter.
I would say that this year has been an average year for honey; the Spring being cold and wet, but a three week warm spell in the summer flow. I have two home apiaries and a couple of smaller out apiaries, one of which outperformed any colony I’ve had especially for honey.
In my home apiaries I had several supers with unripened honey, more than usual I would say. I was monitoring moisture levels in every super that I extracted honey from using a refractometer. I want the moisture level to be 18% or lower, but some honeys will have a higher level, up to 21% for example heather. This year some honey measured 19-20% from the usual summer forage of bramble, willowherb and clover as well as the wild flowers, which is a bit high and can mean that it might start to ferment sometime in the future.
The out apiary that I have in Devon is where my family has an old 1930s holiday chalet. I’d witnessed a swarm coming into the wall cavity of the chalet a few years ago and so set up some bait hives. There are now three colonies there all from incoming swarms, all next to each other and there are energy lines crossing at the point where the hives are located. Although I am a scientist/engineer I keep an open mind on these things and I am a proficient dowser.
With the advent of COVID I haven’t had much opportunity to inspect these colonies in Devon over the past two years, but did put several supers onto them early this year after a quick check to see that they were ok. I haven’t inspected them since, but I did take off two supers from each of two hives….the heaviest supers I’ve removed in my time as a beekeeper. I left one full super on each of them.
Back at home I extracted the honey and weighed it, coming in at an average of 32 pounds a super, 128 pounds from all four. This is pretty good going for me in the UK. The moisture levels of the honey being 16% for all supers. All from two colonies left to their own devices…..swarms and all. Now I will say that the forage there differs from mid Wales, as does the climate of course being close to the sea and at sea level, which might help them to gain extra forage, however, vast contrast to some colonies at home.
So, back to the unripened honey supers, moisture levels from 19-20%; I bought a dehumidifier and stacked the supers with gaps between them and left them in a warm room for several weeks with the dehumidifier running, emptying water from it periodically.
Most experienced beekeepers around here seem to do this as the norm, but I sat there one morning wondering why the bees hadn’t managed to ripen it down further. This honey could easily have started to ferment if left in the hive over winter.
In the meantime I read an article in Beecraft Nov 21 Guy Thompson – thermoregulation within the hive
In this article Guy talks about how the bees process the nectar and what happens to the water vapour that is evaporated from it. He explains that with for example 4 litres of nectar the bees may have to evaporate off 3 litres of water to ripen the honey. It takes 0.5 kg honey to give the bees energy to do this and each litre of water becomes 1600 litres of water vapour. All of this in a hive which might be only 25 litres in volume after taking into account the combs, honey, pollen, bees etc.
What happens to the water vapour? What about the energy from the honey to evaporate this water.
Traditionally, we beekeepers are encouraged to ventilate the hive. Roofs that you can buy from the main suppliers have vents built in, and of course there’s the varroa mesh floor.
The bees in the wild in a tree cavity typically have only one smallish entrance…it is us the beekeepers who force more ventilation as we know only too well that it is damp that kills bees not cold; and so we make sure there’s ventilation.
However, in the situation when the bees are evaporating the water from the nectar, with all the ventilation the water vapour can be lost and with it the energy used in changing its state from a liquid to a gas.
Wouldn’t it make more sense to recover that energy and with it fresh water?
If the hive cavity is such that its atmosphere can be separate from the outside, then it will operate like a condenser. Warm water vapour being lighter than air will rise to the roof (insulated to keep it warm) and will circulate to the outside walls and as it moves down the walls become colder and the water vapour reaches its dew point and condenses giving the bees fresh water.
Ed Clark in his book Constructive Beekeeping (1918) makes the point that the bees in a tree cavity make a propolis envelope, one reason for this might be to retain the water as it condenses rather than lose it to the tree. Propolis is a rosin (hard resin) and as such is a good radiator, meaning that vapour is more likely to condense on it. In the smooth wooden hive the bees don’t make the same propolis envelope, but condensation will take place. More condensation, more evaporation as the atmosphere doesn’t become saturated.
Tom Seeley in The Lives of Bees (2019) explains that he, David Mitchel and others have shown that a typical tree nest can have between 4 and 7 times less heat conductance than a thin wooden hive of the types that are commonly used. They have shown that the cavity in a tree has a stable ambient temperature compared to a thin wooden hive which follows the outside ambient temperature fluctuating by night and day, making it more difficult for the bees to control the atmosphere within. This demonstrates that the bees have much more control of the atmosphere in a tree cavity with only one small opening, than in a thin wooden hive, and even less in one with a varroa mesh floor.
A ventilated hive, particularly with a varroa mesh floor makes it difficult for the colony of bees to get good separation between the hive atmosphere and that of the atmosphere outside, hence much harder for the bees to be able to control the atmosphere in the hive. If the hive atmosphere becomes saturated with water vapour it may be too much for the bees to increase its temperature to allow for further evaporation unless the outside atmosphere allows it. Unlike in a tree cavity where the bees can increase the hive temperature to allow more evaporation and condensation because the outside atmosphere cannot affect the inside that much. In this way the bees can control the evaporation of honey by creating a condenser within the hive.
It is interesting to note that a fully saturated atmosphere at 15 C becomes only 50% saturated at 25 C.
If on a summer’s night the bees are evaporating the water from the nectar and the temperature drops to 15 degrees C, it would be relatively easy for them to increase the hive temperature to say 25 C if the hive atmosphere was separate from the outside and as a result can continue evaporation, but so much more difficult if there is a mesh floor and the atmosphere is similar inside to outside. Who knows how much difference this will make, but it does mean that the bees cannot control the hive atmosphere as well as they might. Maybe the summer of 2021 was one of cool nights and hence nectar evaporation was more difficult for some colonies.
A way in which we can help the bees increase the temperature within the hive to allow for more water carrying capacity is to add insulation and reduce drafts. I’ll discuss more later.
Guy Thompson tells us that there is no way that a typical hive entrance could possibly provide the kind of vapour transfer rates needed at the height of the nectar drying process. The difference in the water carrying capacity of air between the top and bottom of the hive is only around 10g per cubic metre, so a 25 litre space, which a nest might typically occupy, after accounting for the space taken by the comb and bees would need to be replenished some 12,000 times to process just 1 kg honey. The way the bees can influence that space, its size and water carrying capacity is by temporarily moving outside. By bearding, bees try to increase the honey processing capacity of the nest when needed.
Seeley tells us about experiments conducted by Hazelhoff in the Netherlands who measured the volume of airflow. He had a hive with two openings, one at the top and one at the bottom, and on one occasion there were 12 bees evenly spaced across the 25cm lower front entrance, fresh air flowed in at 1.0 to 1.4 litres/sec
Also Peters found that fanning bees distribute themselves asymmetrically around the entrance opening so that air continuously enters and exits at different locations. Fanning bees achieve efficient partitioning of the in flow and out flow air streams by sensing AIR TEMPERATURE which is highest where air is shooting out. Fanning bees use air flow itself, not direct interactions with other fanners to efficiently partition the outflow of hot air and inflow of cooler air through the entrance. He measured airflow as high as 3m/s or 10.8km/hr when temperatures were as high as 36 C.
Both Hazelhoff and Peters demonstrated how the bees can very efficiently change the air in the hive, but these experiments were related to cooling the hive.
I wouldn’t be surprised if the bees use both condensation and fanning to change the air in the hive when ripening honey, however, being efficient they would want to keep the condensed water within the hive as much as possible.
Derek Mitchell also explains that if a nesting cavity is well insulated and lacks a top ventilation hole, then overwintering bees will not have cold condensation dripping on them because the temperature of the ceiling and walls above the bees will be above the dew point. There will be condensation on the cooler walls below the bees, providing them with a fresh source of water.
At my home apiaries I have several poly hives and all my nucs are poly nucs. I have a very high success rate with overwintering nucs in poly hives, even the the Lyson double mating nucs, but also the BS Honeybees double three frame nucs and the standard six frame all made with polystyrene.
The polyhives (not poly nucs) have a wall thickness of 40mm compared to the wooden hives around 19mm. The thermal conductivity of expanded polystyrene is 0.034-0.038 W/m K, of oak its 0.197W/m K, and cedar is 0.099 W/m K
At a thickness of 40mm polystyrene is the equivalent of oak at 0.197/0.036 x 40 = 218mm
At a thickness of 20mm cedar is equivalent to oak at around 40mm
Easily we can see that the poly hives are going to be similar to the oak tree cavity as long as we shut off the varroa floor, which we can do with the insert.
In my example of unripened honey, what I noticed was that none of the poly supers had honey that had too much moisture, it was only from some wooden supers
I also noticed that the inner walls of the poly hives are quite rough and the bees are putting some propolis onto the walls.
It would seem that we can get our hives closer to the tree cavity by using expanded polystyrene hives. I will continue to monitor mine in coming seasons and I don’t intend changing my wooden hives just yet, but I may move to solid floors. I have been inspecting less and less in recent years, but do check at critical times during the swarming period. I also intend to watch the activity at the entrance closely and pay more attention to fanning.
Tom Seeley sent me this article on ‘The Benefits of Providing Good Hive Insulation‘ by John Gaut where John demonstrates how condensation on a perspex cover board in an insulated hive occurs on the outer edges of the perspex, not creating damp in the cluster and providing much needed winter water.
Going back to the two hives I have in Devon; I left them pretty much to their own devices and found the supers pretty well glued together. One of Tom Seeley’s recommendations is to leave the colony alone and not constantly breaking it open to inspect it. These two hives had removed all draughts, one was on a solid floor the other a mesh floor but then on a full wooden base. Although they were traditional wooden hives they coped with the fluctuating temperature well and including the third super that remained on each one, they managed to process around 100 pounds each. I don’t know if they swarmed, I will continue to monitor their progress.
It’s interesting to see the entrance to one of these hives where the bees have made two holes in a propolis wall. I think this it to allow for fanning; warm air out of one hole cold air into the other.
Finally, I don’t want to have to use a dehumidifier to ripen honey in the future, I want to give the bees every opportunity to do it themselves!!!
This article is written to provoke thought and with the idea of trying new things, but as beekeepers we must be aware of the issue of damp in the hive especially if things go wrong for the bees. We must be aware of the issue caused by Varroa and even if we don’t inspect the colonies, we must check for the varroa drop levels details can be found at Beebase and treat if and when necessary, Tom Seeley points out that bees are very good robbers and if a colony has died out because of varroa, the varroa left behind are very good at jumping onto robbing bees. In his experiments Seeley found that this caused big jumps in varroa levels within his hives. Make sure that any colony casualty is removed quickly
My thanks to Guy Thompson for his article ‘Rethinking the box’ in Beecraft Nov 2021
Oliver Sacks book The River of Consciousness highlights among other things the discoveries made before their time, particularly in science discoveries have been made but ignored by the peers of the time for many reasons, they are too far removed from the thinking of the time. Only to be ‘re-discovered’ many years later. Ed Clark’s work on condensation in the hive in 1918 was widely ignored by the beekeeping community of the time as the main focus was on ventilation, Thermodynamics is not the easiest of concepts to grasp, if grasp is the right word. I’m lucky in that being a chartered engineer, an applied scientist I studied thermodynamics at undergraduate level, one of many subjects covered at the time. Ed Clark’s work makes sense to me now that I’m also a beekeeper…..
A bee settling on a flower has stung a child
And the child is afraid of bees and declares that bees exist to sting people.
A poet admires the bee sucking from the chalice of a flower and says it exists to suck the fragrance of flowers.
A beekeeper, seeing the bee collect pollen from flowers and carry it to the hive, says that is exists to gather honey.
Another beekeeper who has studied the life of the hive more closely says that the bee gathers pollen dust to feed the young bees and rear a queen.
A botanist notices that the bee flying with the pollen of a male flower to a pistil fertilizes the latter, and sees in this the purpose of the bee’s existence.
Another, observing the migration of plants, notices that the bees helps in this work, and may say that in this lies the purpose of the bee.
But the ultimate purpose of the bee is not exhausted by the first, the second, or any of the processes the human mind can discern.
The higher the human intellect rises in the discovery of these purpose, the more obvious it becomes, that the ultimate purpose is beyond our comprehension.
Leo Tolstoy – War and Peace