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Supposition and Observation

In the days before the advent of moveable frame hives, books were written concerning bee behaviour based on supposition, when observation was not possible.

Since those times, through constant repetition, some of those concepts have stayed with us and are accepted as correct. The long period of winter is a time when hives are left alone and I do not consider standard theories on wintering logical or capable of withstanding scrutiny.

The first dogma is that the colony undergoes a broodless period late in the calendar year and then as day length increases the queen starts to lay again initiating a slow but increasing level of brood rearing.

This has never been demonstrated in practice. When colonies are killed accidentally during the time they are reputed to be broodless, by unexpected flooding, or their host tree being uprooted in a gale or some such calamity, any beekeeper examining the wreckage is wont to remark, with surprise, just how much brood was present!

A sound principle in beekeeping is that colonies should only be examined when there is a definite reason to do so. Ordinary beekeepers see no reason to examine bees throughout the winter period and so do not.

There have been accredited researchers however who have wanted to know exactly what is happening over winter. In England the NBU (National Bee Unit) gauging the potential threat of Tropilaelaps clareae, which needs brood to survive (unlike varroa destructor, which can live on adult bees) monitored hives over winter in five dispersed locations, these ranged from Dorset to North Yorkshire. In this case individual colonies were used but they also monitored a number of colonies at the National Bee Unit, York.

Their findings were that a short broodless period does occur but when this happens is quite unpredictable and each colony follows a different pattern i.e. there was no period when all colonies were broodless. (Reference 1)

There were two studies in North America very similar to each other to examine winter brood rearing in outdoor wintered colonies.

The earlier study from 1971 to 1974 was done in Connecticut at an altitude of 300 metres above sea level, University of Connecticut.

The other from 1990 to 1992 at Beaverlodge, Alberta, University of Guelph. Both sites having cold….very cold winters.

From November through to March/April colonies were selected at random at three or one week intervals depending on the site and killed by gassing. The dead hives brought indoors for a count on bee corpses to give absolute population and egg plus brood levels. These readings gave a “snap-shot” of those colonies on that winter day.

In Connecticut they recorded a brief broodless time, in the last week of November or first week in December. In Alberta there was no period when no brood was observed with averaged results.

These results must be treated with caution due to the small numbers of colonies sampled over a short time frame, however they hardly support winter broodlessness as a norm or predictable.

The American results differ from UK ones, in that they saw least brood Nov/Dec and a steady rise thereafter, in England the timing of minimum brood rearing was very variable.( References 1, 3 & 4)

While it existed the College of Agriculture of the North of Scotland in Aberdeen did a good bit of looking at over wintering. Over the winters of 74/75 and 75/76 colonies were examined regularly, whenever weather permitted.

Like the subsequent NBU results no predictable period of broodlessness was found. Unlike American observation, stops in egg laying were seen more often in the New Year.

To investigate winter broodlessness some queens were caged in the winter but with worker access so no egg laying. These colonies developed dysentery and died unless the queen was released in time and began laying.

This indicates that brood rearing is essential for the winter cluster to survive. A feature of these experiments is the small numbers of colonies used so a normal range of values can’t be given.

In probably an exceptional instance in Aberdeen one colony reared some 10,900 bees from 5-11-75 to 15-02-76 or half the maximum population some stocks achieve! ( Reference 2)

Anyone who has waded through the foregoing could say, “So what.” Fair comment, but now we have varroa and need to control it, a knowledge of what is going on within our colonies over the winter period, the perceived time when treatments are most beneficially given is important.

The second dogma I have difficulty with is the accepted teachings on the mechanisms of the winter cluster. A colony going into cluster can be observed, similarly the contraction of the cluster with decreasing temperature and individual bees moving from the cold exterior of the cluster into the warm central regions and vice versa.

With temperature probes the internal and external cluster temperatures are readily established. The accepted theories concerning these observations I find difficult if not impossible to accept.

The external cluster temperature is maintained at some 8 degrees centigrade, which approaches, if not is, the minimum temperature a bee can start from, to build up body heat to the level needed for activity. Once body temperature falls below 8 degrees the bee perishes.

It is irrational to me to suggest that a bee who after all has a level of choice of action voluntarily puts herself on the edge of life and death without any benefit to herself as standard teaching states. This is even more bizarre when her sisters are feeding and “basking in luxury” in the warm cluster centre.

Standard teaching is that heat is generated at the cluster centre with enough flowing to the outer layers to maintain that 8 degree minimum.

As temperatures decline the cluster shrinks and the outer layers of bees are more tightly packed to improve the insulating qualities of the outer shell.

Now to maintain external cluster temperature this improved insulator also has enhanced heat conductivity. Such a concept is self contradictory so I suggest quite impossible.

A basic method in the sciences is to draw up theories to give possible explanations for phenomena we do not fully understand. As new knowledge or new thoughts evolve theories can change to accommodate this, or fresh radical theories can be put forward.

Not accepting standard teachings on wintering as they stand the concepts put forward by Bernard Möbus have a logic that appeals. This again is a theory yet to be proved or disproved. (Reference 2)

Bernard continued from experiments that had been run at The College of Agriculture of the North of Scotland on wintering colonies of bees. When super colonies were created, by uniting two large colonies in late autumn he observed, after cluster formation, such colonies lost large numbers of bees when cleansing flights occurred, rather than cleansing the bees sought water, chilled and perished.

On dissection these deceased bees were found to be dehydrated. Similar results came from a normal colony wintered in a very well insulated hive. The suspicion arises that clustered bees that are not subjected to low temperature dehydrate.

Bees naturally strive to maintain a reasonably high body temperature and as a mass will form a cluster when cooled. If a small number of bees, fewer than can cluster, are cooled to external cluster temperature, a measurement of carbon dioxide production indicates that those bees are metabolising sugars to maintain life and producing more water from metabolism than they are excreting through respiration.

By the same token bees held static at cluster centre temperatures excrete more water than they produce metabolically. ( Sugar + oxygen metabolised gives energy, carbon dioxide and water)

If it could be shown that a mass of bees in a cluster behaved as do these small groups, dependant on their position, then there is a dynamic of water balance driving the movement of bees from centre to outside to centre on a continuous basis.

The external bees are building up a water surplus while the central bees are dehydrating so changing positions maintains their water balance. It would then be the outside bees who are consuming stores to metabolise so producing heat and they are where the stores are. Even though on the border line of life and death they have control of their own destiny.

It should be borne in mind that water balance is more critical to survival in extreme situations than food. In this scenario bees would be able to survive for long periods in cluster with a potential limit being the accumulation of faecal matter. Winter flights are so aptly called cleansing.

Rather than being a minor intermittent activity brood rearing in the winter cluster is rather, an almost constant state which might be the driving factor in cluster dynamics.


  • Brown, M.A.; Thompson H.M.; Bew M.H. (2002) Risks to UK beekeeping from the parasitic mite Tropilaelaps clareae and the small hive beetle, Aethina tumida. Bee World, Vol 83 No. 4
  • Möbus, B., (1998) Brood Rearing in the Winter Cluster. ABJ 138: 7 511-514 & ABJ 138: 8 587-591
  • Avitable, A., (1978) Brood Rearing in Honeybee Colonies from late Autumn to early Spring, Journal of Apicultural Research 17(2): 69-73
  • Szabo, T.I., (1993) Brood Rearing in Outdoor Wintered Honey Bee Colonies, ABJ vol 133: 579-580)