Brood Rearing in the
By Bernard Mobus, N.D.B.
Brood Rearing in the
By BERNHARD Morsus, N.D.B.
Winter is an annual event, and the cold season will be here again before we know it. Wintering losses of honey bee colonies are becoming more frequent and serious now since varroa is infecting colonies worldwide. Beekeeping is in retreat, especially among amateurs and hobbyists.
And, we must admit that even a low level of infection in spring can have a disastrous effect on the colony towards the late summer. Following the first anti-varroa treatment in spring. a small number of surviving mites increases steadily throughout summer when no fomr of control can be administered effectively. When fall comes near. and bees prepare to face the coming winter by rearing a last batch of brood. maybe thousands of mother mites are entering the cells and they, and their progeny, will draw the life-blood of the very bees which should become winter
° the very bees pre-programmed to store additional reserves of protein and fats for winter – in order to become. . _
‘ the very bees which should survive the coldest part of winter in a partial domrancy. – and survive to be. . _
~ the very bees which should rear the first batch of brood the following spring and carry on the species.
Autumn treatment against varroa, when all brood has emerged and after the honey harvest has been removed, may come too late; all emerging bees are damaged bees. are physiologically unfit to face the cold and are prone to disease. Many of them die, too early in life. thus weakening cluster strength and reducing its chances
ln order to improve our colonies chances of successful wintering. we must first Ieam all there is to leam about Varroa and its control. But we also must learn more about wintering and about the winter cluster. Of course, books are full of the traditional version, and the old recommendations also tell us that one should leave the wintering colonies alone, and never look into hives or interfere with the bees – or hives. But finding out how things work is an old human failing, and over the years beekeepers and scientists have poked mercury thermometers into the cluster, have gassed whole colonies before taking the hive apart and examining combs minutely. Recently, they also have taken the easy way out and have introduced lots of thermocouplcs into hives in order to take regular readings of the temperatures of the cluster and of its surroundings and have recorded them on a daily, hourly. or more frequent basis. The scientists then made their computers analyze the readings and produce pretty graphs and isothermal contour maps of the winter cluster – which they never saw! Pretty. But is that the whole story?
True, it is best to leave bees alone once the colonies are well fed and safe from the wet and the driving snow. Yet in the l950s. a Dr. Jeffree did try to discover what is going on in the winter cluster, and he examined about 360 colonies over a period of I0 years while he was at Aberdeen. Scotland. He tells us that it is all right to look into hives, provided the air temperatures rise high enough to permit cleansing flights and allow bees to retum
home safely afterwards (Jeffree. E.P.1956). He discovered patches of brood at any time of the winter period. Although the size and their occurrence appeared to increase towards spring. Furthermore, he could not relate their occurrence to climatic conditions affecting the whole of the apiary. Most hives were inspected once
only in each winter, but among the seven colonies which he examined repeatedly weather permitting – he found in two of them evidence of stops and starts of brood rearing.
All right. the winters in the north of Scotland can never match those of the northern states and of the Canadian
provinces. but wintering in a cluster relies on inherited patterns of social (and individual) behavior which guarantees survival, and the basic principles reside in the genes of all bees of the European races of Apis mellifera L. Variations in temperatures are only a matter of degrees, not of principles. And, although the two winters were exceptional. sometimes the winters can also be bitter and prolonged in Scotland.
Dr. Jeffree’s work, as well as that of many other scientists, was of great interest to me after l had discovered brood rearing in my hives in Lincolnshire one winter. Pondering over the reasons behind such an activity which. of course, could cost the lives of colonies through starvation or nosema disease. the search for an answer became a veritable compulsion. l took part in wintering surveys of food consumption, and was surprised at the varia-
tion in food consumption between colonies. After that, I started to examine my own colonies whenever l could. When I was appointed to the Advisory Post at the College of Agriculture of the North of Scotland at Aberdeen, my investigations into the problem of brood rearing in the hive-locked winter cluster were intensified. During the first two winters, nearly all colonies in the Craibstone apiary (and my own) were subjected to regular inspections (weather permitting), and some of the colonies took part in other experiments which included the caging of ueens (with access by workers). as well as the formation of ‘super colonies’ by uniting strong colonies to form one unit.
ln this part we will first consider the work of the examinations, and the Tables I and 2 give a representation of my findings in the winters of 1974/75 and 1975/76. The two winters gave me numerous chances for examinations, with mild spells luckily occurring roughly (and randomlyl) every three – four weeks. So as to avoid artificial engorgement, the hives were opened without smoke and the bees settled quickly without further aggression
within minutes after closing up. Although it must be admitted that – possibly – more bees used the disturbance for a chance of an additional cleansing flight – and my protective clothing was needed for another protective reason!
Whenever a patch of brood was discovered, it was not only measured, but also minutely examined for the presence of eggs, larvae or pupae. and their presence was registered for every face of comb (Tables I and 2). Explanations for the study of the tables are: Each field is divided into three: eggs, larvae, pupae; as indicated below the date (e; l; p). Each line corresponds to one frame, and a slash (I) represents the mid-rib of that comb. A
plus sign (+I+) on both sides of the slash means that eggs, larvae or pupae were present on both faces. Sometimes one look was enough to see that the older, larger larvae were missing, and so particular attention was paid to any irregularity in the pattem of larval age. Whenever only eggs – and no larvae – were found, or at other times only one-day, two-day or three-day- old larvae were seen in the depth of cells, this was recorded separately. This is repre- sented as a figure 1, 2, or 3 instead of the plus sign which indicates the presence of
larvae of all ages.
Of course, beekeepers immediately recognize that here the queen had stopped laying for a while and that she had just started again after a ‘brood stop’ had occurred. Some colonies showed two or three of these stops, and they are identified with exclamation marks in the appropriate column. In one colony the few remaining capped cells looked suspicious and their contents were removed. They were dead, fully developed pupae, but the imagoes looked shrivelled. They were mummies only and showed no sign of AFB or EFB.
An asterisk, (I*) not a cross, indicates these findings.
The tables show that some brood could be found in some colonies during any of the winter months; even November and December were not without such activity. True, the number of colonies starting to rear brood and the size of the brood patches increased towards the end of the winter period. But the number of brood stops
(and starts) also became more numerous towards spring.
The sum of the brood areas discovered (in centimeters, and not adjusted to account for longer of intervals between inspections), is recorded at the right of the tables, and it shows wide variation from I47 cm’ to 2730 cm‘- all in the same apiary. Allowing for a cell density of 4 worker cells to the cm’, the number of bees born during ‘dormancy‘ ranged from a low 588 to l0,920 bees. The last figure represents a veritable and generous 2 lb. pack-
The patterns of egg laying also are of passing interest. In some colonies the small patches of brood were on opposite faces of adjacent combs ~ and the queen did not have to leave the centre of the cluster, while in Col. 2 (Table 2) the queen had to move over into the neighbouring passage to lay her eggs on the other face of the
same frame-a colony with too small a cluster to support a larger brood nest? No. a spring examination showed that the two colonies were firing on all cylinders once March had arrived and some foraging activity had recommenced.
Only one queen died during the winter examinations of normal colonies (Col. No. 24; Table 2). We have always been warned about the danger that bees may ‘ball’ their queens when interfering at wrong times, but the records show that in this case pupae were still emerging 30 days after the last inspection. ‘l`his implies that eggs were laid for at least one more week after the last examination, and that the queen must have died from ‘natural
causes‘, maybe old age.
lt is just these details of the careful inspections which made the work so important. Although brood rearing in win-
ter has been known to occur for a long time, sometimes by accident, no other work has supplied the clear evidence that brood stops and starts occur so frequently and are probably an important part of winter brooding.
Even hundreds of thermocouples registering every five minutes cannot show up the cessation of egg laying –
nor its re-initiation. After all, brood rearing is an on-going process and lasts three weeks (possibly longer in a winter clusterl). so brood nest temperatures will be maintained at the high level of 35°C as long as living brood is present (unless brood dies for some reason). Yes. in later years we also did a lot of recording of hive and cluster temperatures, but that work never provided us with the same insight into cluster behavior as our direct inspec-
tions of winter clusters.
Yet it must be the initiation and cessation of egg laying by the queen which should provide a clue to brood rearing in mid-winter. Even among bees the old saying applies: “Every baby costs its mother a tooth.” So we do need an explanation for the seemingly ‘wasteful’ production of food and for the increased wear and tear this brings for the ‘dormant’ bees. but which are now sacrificing ‘life and limb’ important protein reserves to raise young bees. Bees are thus laying themselves wide open to early death and nosema disease. Furthermore. we also need an expla-
nation for the need of such ‘wastefully‘high cluster temperatures – which could lead to starvation of the colony as a whole.
The last sentence is not scaremongering. Hives had been weighed before winter started, just when flying had stopped. When milder weather and flight for water, for early pollen and nectar was becoming possible again on a regular basis, we called it quits and weighed all hives once more. A superficial examination of the listings showed a relationship, and when the sum of the brood areas and food consumption were statistically evaluated, a
very high correlation: r = 0.92 was obtained for the two winters and the 33 hives. Further statistical analysis even supplied the following regression equation 2 Food consumption = 4.1818 kg + 0.000375 (kg) per cm’ of brood.
Again, these values apply for the increase in food consumption – demanded by brood rearing over and above a basic minimum – only in the Craibstone apiary just outside Aberdeen over the two winters. But in principle they will stand for all true wintering in any climate.
The results are so clear and significant – in spite of’ the individual patterns -and areas of brood rearing and the greatly varying food consumption, that we can say the following:
Wintering is a cluster-specific experience, and any brood rearing in mid-winter costs additional energy over and above the basic energy requirements of a non-brooding colony.
Of course, we must never forget that winter brooding can also pemiit Varroa to ‘rear brood’ in mid-winter, and that many more young and strong Varroa mites will have a head start once brood rearing commences in eamest. So why do bees rear brood in mid-winter? How can we stop it? Furthermore: Should we try to prevent
brood rearing – and how?
Well, some other experiments do seem to answer the questions. at least the last question. During both winters some queens were held in the center of the cluster in a small cage of excluder material in order to prevent
them from laying eggs (while still giving bees ready access). Most of these colonies developed dysentery within three – four weeks and grew weak and weaker and hardly one stock in this group recovered when the queen was released in spring. ln only one case did everything tum out all right afterwards. The queen was caged when brood
rearing had started and before any cells had been sealed. When, six weeks later. signs of dysentery were seen, she was released from her prison. Four weeks later, at the first inspection of spring, there were 822 cm’ (about 3250 cells) of brood on two frames and no more dysentery. The records show the remark made at that time: “population greatly reduced”. (None of these colonies appear in the tables, and none were included in the cal-
culations of statistical analysis.). So it seems that – sometimes – NOT rearing brood is even more stressful than doing so!
‘Super colonies’ were created during the second winter period. Such colonies never reared any brood. ‘l`hey had been formed as an additional experiment after reading Dr. .leffree`s other paper in which he disproved the age-old advice that “the best packing for bees are more bees”. He had found in his work on the influence of colony size on the rate of population losses, that the weak stocks. as well as the very strong colonies, lost more bees than what he called ‘nomial sized‘ colonies. lt was for that reason that I decided to sacrifice four strong stocks in autumn and to unite. in each case, two of them by the newspaper metl1od after removing one queen. In both cases uniting went off peaceably. and all seemed well. Bees were frequently flying from these ‘super colonies’ and their (light was fast and direct – not to rob a weak stock. but to a source of water.
After a longer spell of cold. the weather relented again to permit cleansing flights and inspections. Both ‘super colonies’ had massive. disastrous losses. and bees were clinging to the hive sides, to hive stands, to grass blades as if the ‘Isle of Wight’ disease (tracheal mites) had struck another blow. But trachea were clean and healthy. and no Nosema was found. Bee samples taken came to life again once they were in the wamith of
the laboratory. With an idea forming in one`s mind. the bodies were then weighed individually before bowels and honey stomach (with contents) were removed for further investigation. These produced the following results.
When compared with samples taken from standard and dyscntcric colonies (in that order). (See Table 3)
The bees from the ‘super colonies’ had no excuse to tly on a cleansing tliglit. their
Distribution of body weights (empty*) of bees from ‘super’ and dysenteric colonies.
*After withdrawal of sting apparatus, rectum, bowels and honey stomach.
(empty) body weight shows that blood quan-
tity was low and it was extremely difficult to
obtain a sample. In fact, the bees were dehy-
drated and had llown en masse for reason of
dire thirst! And, coming from a warm cluster
without having to contribute to heat genera-
tion. they chilled by the thousands before
reaching their goal: water.
Biidel, A. (1948) Die Temperatur in der
Beute. Imkeijieund I0 ; 89
Farrar, C.L. (1963) The Overwintering of
productive Colonies. The Hive and
the Honey Bee, Roy Grout (Editor),
Dadant&Son, Hamilton. lll..U.S.A.
Available all summer and fall
Free, ,].B. (1968) Engorgement of honey
by worker honeybees when a colony is
smoked. .l.Apic. Research 7(5) : |35 ;
Jeffree, E.P. (1956) Winter brood and
pollen in honeybee colonies. Insect
sociaux 3: 416 – 421
_Ieffree E.P. & Allen, M.D. (1956) The
inllucnce of colony size and nosema
disease on the rate of population loss
in honeybce colonies in winter.
.l.Ecrm.En1om. 49(6) : 831 – 834
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American Bee Journal
By Bernhard Mobus NDB
Beekeeping Adviser for Scotland
Part III – The Sink:
Damp and Condensation
ln this instalment we had hoped to get to grips with the problems which we originally set out to solve: those of damp and condensation in bee hives. In the two previous articles we have learned about certain universally applicable laws of physics, we have looked at the biological ‘animal’ inside the hive with its needs for dormancy on one hand, and at reproduction through brooding. These are the cyclical habits which evolved in honeybees in response to annual climatic adversities. We now understand that when water evaporating from the colony disperses freely into the atmosphere, air becomes the ‘sink’. On the other hand, if dew-point is reached within the hive, condensation will form on cold places such as crown board, floor, honeycombs or hive sides. The hive then becomes damp and soggy; the hive becomes the sink.
Of course, when beekeepers use the term ‘hive’ , this will mean different things for different people. Shapes, sizes, frames, capacity and construction vary considerably. After all, hives are man-made and did not ‘evolve’ ’ although its construction was constantly ‘improved’ over the years for easy exploitation of the bee’s productivity – and the bee had very little say in the matter. Hives now contain frames for easy inspection, manipulation and extraction. Hives were made for KEEPING bees, not for keeping BEES. Development involved mainly technological aspects, rarely were biological aspects the reasons for the ‘improvements’ (unless the use of insulating plastics comes into that category). The problems arising from the invention of modern hives are with us to this day.
In the old days the wicker or straw skep ruled supreme in Northern Europe. Clay tubs, earthenware pipes and tubes were preferred around the Mediterranean, and cork and bark hives were used where such material could easily be obtained from natural sources. In colder climates special shelters were built for rows of skeps to keep them dry and protected. In the Luneburg Heath the large scale beekeepers built square ‘bee towns’ by means of shelters, with the south facing one having room for up to 60 skeps for wintering, the other sides able to hold 180 more to accommodate the ensuing swarms and casts and keep them safe and dry. No wonder that, in most countries east of the Rhine, the massing of skeps was popular and traditional and Dzierzon’s books and teaching may have been responsible for its survival as bee-houses into present days. On the other hand, it may well have been the severe cold of continental winters which ‘taught’ beekeepers to herd hives together for the mutual benefit of colonies.
In Britain we find individual bee boles, sometimes in rows, and they can still be found in old walled gardens from John o’Groats to the Home Counties. The early settlers may have introduced this setting up of individual hives into America and, influenced by the books of Langstroth and Dadant, the free-standing hive became the modern hive throughout the world. Even today, and taking the world as a whole, the Langstroth design and dimensions are predominating by about ten to one. In Britain the hives now of wood were protected against the wind and rain by individual shelters, the outer lifts of the well-known WBC double-walled hive. For Britain’s mild climate that proved sufficient in most winters, yet even in America heavy winter losses in the cold climate made beekeepers of some regions try out shelters and cellars in the hope of improving the survival of bee colonies.
These attempts brought their own crop of problems, but we cannot discuss them here. In the most difficult egions beekeepers finally began to kill all colonies and bought fresh packages every spring. Even in the good old days of skeps, wintering losses due to starvation occurred frequently after disastrous seasons. These were mainly due to starvation after bad summers and late swarming, On the other hand, losses of stocks with ample stores left over (and Nosema) are more a problem of ‘modern’ , ‘efficient’ and single walled hives, and beekeepers tried out many ‘improvements’ to overcome them.
In such killed-out colonies it was often noticed that condensation had formed in the hive on crownboards, combs and hive sides and ’damp’ was blamed for the demise. Of course, surviving colonies were never inspected before warm weather and strength had returned, and damp was, by then, not apparent to the same degree; thriving colonies showed no damp by that time. Even a cursory glance in winter would not reveal the damp sides of hives, nor the soaking floor. For fear of disturbance the beekeeper did not look very far. Nor would beekeepers draw the right conclusions when they cleaned hive floors by late spring to remove the caked debris in the corners. They did not realise that a floor with caked dross had been a dripping, sodden mass during winter. By spring-cleaning, the colony’s warmth from the brood nest had dried wet debris to a hard cake. Usually, directly under the cluster’s position, the floor shows no caking and there it had remained dry and clean throughout winter. On any fine day bees had been able to remove fine wax debris and dead bees, or fan and ventilate efficiently, thus blowing the dirt into the corners and under the carpet. Few beekeepers realised that no condensation had formed under the cluster, here it had been warm, therefore dry, throughout. The answer to a problem was there for all to see; the
questions were never asked. Schemes were developed to cure only the visible damp, that underneath the crownboard; the floor was not regarded as needing attention – apart from spring cleaning.
Pre-historical Notes: The Beeway
At this point we must look at the ventilation of the bee’s ‘home’ from another angle and ignore Wedmore’s book on the subject. We must look at the ‘beeway’ , probably one ofthe most important factors in the life of honeybee colonies. It is so important that we can probably say that the bee evolved to its present size because of the properties of the narrow beespace. Maybe you are content saying that the beeway is beeway-sized for bees to pass through. Well, in a way, you are right. Certainly, Langstroth shouted “Eureka” when he came to the conclu-
sion that a correct gap between hive timbers and frame sides was ‘respected’ by the bees. He had found that in larger gaps they constructed brace comb, and bees closed with propolis any gaps which were narrower. He then constructed a number of hives experimentally, together with frames constructed on the basis of his discovery, and his bees proved him right. His ‘Langstroth hives’ are still with us. On the other hand, this discovery opened the way for many inventors with two year’s experience and a buzz-saw and local variations of hives incorporate the principle of the beeway as the main feature. Yet for the honeybee this beeway means far more than is implied by its adoption by man for hive plans and construction.
As so often in this series of articles, maybe it is again best if I let my grasshopper mind take a side-jump into other fields before returning to the beespace and, ultimately, to our subject matter. Earlier on we had looked at the free diffusion of gases by means of molecular motion and collisions due to kinetic energies. Taking now a narrower, beespace view, we must look at aerodynamics, the study of the motion of gases and air, in tight spaces and around obstacles. Scientists can do this work in specialised wind tunnels but, fortunately for us here, most rules governing gas movements are comparable with those of fluids. Looking therefore at the flow of river water can give us a good idea of what is happening when air moves past, around or between obstacles.
Far from the river’s bank the flow of water is rapid. Straight, smooth, ‘laminar’ flow predominates. Friction nearer the edge slows the flow, and in contact with land, eddying currents (turbulence is the word used by scientists) appear close by the bank. Finally, going closer still and temporarily taking a microscopic view of the interface between water and soil, we would find that the water barely moves. Here we have the ‘boundary layer’ , and here we find that ‘flow’ stops altogether and that molecular motion prevails. The same effect, that of a ‘still layer’, can
be found when we look at the flow of air in relation to surfaces.
The aerodynamics of boundary layers certainly have an important influence on flying (even for the bee), but they must also be considered when it comes to biometeorology, the study of the effect of weather and climate (including microclimate) on life. Disregarding the river now, we find that strong winds can whistle far above the ground, yet leave lower layers of air moving much slower. Right between ground vegetation we find a calmer situation and a special micro-climate for plants and insects. Finally, in contact with leaves or the soil, boundary layers are ‘still air’ and temperatures rise quickly whenever the sun shines.
One bio-meteorologist has measured the insulating effect of such immobile air cushions. He found that the temperatures within the boundary layers, when translated into distances which can be visualised, came to the surprising temperature gradient of 125,000oC (225,000oF) over 100 m. (P.P.Lowrie). Impressed? Good.
Nevertheless, it is no wonder that on sunny days we find a mirage effect due to hot, refractive air over the asphalt of country roads – even when a bitterly cold wind is blowing!
A bee hive is full of passages between combs and every rough surface of comb has a boundary layer. Narrow, beeway-sized passages do not only exist between hive walls and frames as a constructional detail after Langstroth’s discovery. They are of far greater importance between the stores of sealed honey above and around
a brood nest. The reasons for this becomes obvious.
Brood cells with eggs and larvae, or with pupae under porous cappings, must be kept warm within fine limits at the smallest cost in energy to the community. Yet, the cells containing breathing, metabolising larvae and pupae need Ventilating to provide fresh oxygen supplies and to eliminate carbon dioxide (CO2). This can take place either through passive diffusion or active fanning. ln the brood nest, and also between empty honey combs where the wax has been nibbled back, the beeway is destroyed and the passages are wide enough for two, three layers of bees to jostle past each other. Here bees can nurse brood underneath them, and the space still permits ventilation by natural diffusion or, if necessary, by fanning. This latter activity is usually triggered off as soon as temperatures or the concentrations of CO2 or humidity rise above the level for comfort. But more about
that later. Between brood comb the wider passages permit air movements from fanning bee to fanning bee until some of it passes out of the hive.
On the other hand, we must remember that the passages between brood comb vary slightly according to the spacing we adopt for frames. Hoffman side bars provide for Langstroth’s 35 mm (I 3/8”) spacing. Because the thickness of worker comb with sealed brood is about 24 mm (about l”), this leaves a passage of 11mm (7/l6”) for two bees at a time. Where drone comb is constructed on both sides, thickness of comb expands to 33 mm and adjacent comb, when spaced 35 mm apart, must be cut back by bees to allow access to open drone brood.
For British Standard hives beekeepers usually have the choice between 35 and 38mm (1 1/2”) spacing when ordering Hoffman side bars. Frames with metal ends (1 15/32”) and the wider Hoffman frames leave a gap of 14 mm (9/l6”) between brood comb. This gives enough room for 3 bees and provides for better ventilation of passages, even drone brood can be nursed on adjacent sides, still allowing for a single beeway between comb after being sealed.
Above and around the brood nest we find fully drawn out and sealed honey crowns and rims with a beeway-sized gap between cappings. An insulating ring of pollen stores may exist between the brood and the honey cells. Between sealed honey reserves, comb passages are of beeway dimension (5 – 7 mm) only, and only one
bee at a time can squeeze through them. Here they exploit the protective doubleboundary layers to the full and prevent the free escape of precious warmth from the brood nest by laminar convection currents by means of the natural aerodynamic barrier. This is especially obvious in colder climates where bees have difficulties in maintaining an optimum brood nest atmosphere due to the greater differences between the water vapour pressures within the brood nest and the ambient ones.
Non-native, prolific and profligate bees may not show this character, and wide passages all around leave their brood nests vulnerable to humidity losses and dehydration. Such colonies often fly earlier than any others – and before flowers begin to yield nectar. The colonies fly enthusiastically – for water. In a bees’ paradise where nectar flows freely, where absolute humidities are high, and where bees have no problem, the pollen barrier and honey rims vanish from the sides and even sealed stores are moved out of the way of the expanding brood nest.
An upward flow of air activated by gravity (warm, moist air being lighter than cold and dry air, a chimney effect), would seem the easiest way to remove all noxious gases and excessive humidity from brood nests and from ripening honey. lndeed, Wedmore suggested that hive ventilation is driven by this ‘air motor’ of rising (escaping) warm air. It would require no activity on the part of the bee. On the other hand, the word ‘chimney effect’ says it all: heat is used – indeed wasted – to drive the system and this is something bees cannot afford – except in
a paradise where bees do not have to think of survival through a long, cold winter.
Conservation is a watchword spelled by the bee in capitals.
ln order to avoid wasteful losses of heat through upward ventilation, bees have chosen to reduce the passages between honey comb and surrounding the brood nests to such a narrow gap that it effectively applies the brakes against the rapid escape of warm, moist air. Here the bee-way rules supreme and reduces losses of warmth and humidity to slow diffusion. This relies mainly on partial pressure differences and the kinetic energy of molecules. We have to learn to accept that the seat of the winter cluster, at first nearest the entrance – and where the last batch of brood emerged, is the warmest place in a hive full of honey reserves. For aeons bees have chosen cavities in trees or rocks for their home, and usually began drawing comb right at the ceiling where little or no upward ventilation was possible. First brood combs were spaced so that nurse bees could incubate eggs and take care of brood on both sides of brood comb – still leaving room for natural ‘ventilation’ through diffusion. As honey surpluses began to accumulate and ripen, they were stored in the cells around and above the brood. Honey cells were extended in depth and, when sealed, the gap between the cappings was so narrow that only a bee could squeeze through.
This brought the layers of still air on both sides of the roughly surfaced, capped honey reserves so close to each other, that movement of air was restricted and the beeway became an aerodynamic barrier against the rising currents of warm air. Below the brood combs this barrier does not exist, and bees can permit the forces of diffusion to take care of problematic waste gases. When levels of carbon-dioxide or humidity rise, bees begin to fan and relieve the situation along the line of least resistance: downward and away from the brood nest.
ln winter too, the beeway-sized passages between honey stores avoid speedy loss of warmth through upward motions of air. At all times bees actually seek out the most ‘comfortable’ , the warmest place of a hive, for wintering. When polystyrene insulation is experimentally placed above the crownboard the cluster will slowly migrate to the under-side of that board and will settle right between the solid slabs of honey where the warmth cannot escape because of top insulation. When two nucleus boxes are together under one roof, the two colonies will move to adjacent walls so as to benefit from the warmth of the neighbouring cluster while, on its own, each colony would consciously avoid contact with the chilly outside walls. ln hives made from insulating material (expanded polystyrene), the cluster snuggles up against outer walls. lt must therefore be obvious to even a
blind man that where bees normally form their winter cluster, right underneath the beeway-spaced honey stores, they will be in the ‘warmest’ part of the hive, even though it could be next to the entrance and next to the deepest frost. Protected by the beeway above, less warmth escapes than is commonly realised.
Although Langstroth, as the father of the movable frame hive, ‘discovered’ the beespace and advanced beekeeping technology by exploiting it as the inviolate space surrounding individual frames, he never realised its bio-meteorological significance.
Yet the importance of the beeway as aerodynamic barrier is reaching so deeply into colony life, that we must ponder about the possibility that the properties of the beeway, through evolution (which could, theoretically, change the size of the honeybee by adaptation – but which can not alter the laws of molecular motion or the effects of boundary layers), led to the bee’s present size. Between vertical combs with bumblebee-sized passages, a strong chimney effect could well take away all damp, CO2 and other products of metabolism, but the laminar flow
would create a chimney effect which would remove all heat and would let bees perish from starvation in the cold.
We enviously watch bumblebees fly at lower temperature than honeybees, but its colony cannot survive our winters. For a vertical, multi-comb design, evolution had to strike a happy medium between the advantages of a smaller bee in a more efficient brood nest, and the disadvantage of smaller body size. Our bee is the end result of millions of years of experimentation.
We now can see how deeply evolution has affected the honeybee and its natural home. Beekeepers have taken over some of the benefits, often without realising the factors involved. Once successful as keepers of bees, they began to exploit the bee and modernised technological aspects. Supering and extraction are coming to mind. Often they ignored important points when they forced bees into manmade hives and made the colonies winter in them. They often used anthropomorphic arguments to back up their ideas and, thanks to the adaptability of the
honeybee, they often ‘got away with murder’.
Wooden hives of modern design go back about 150 years to Langstroth’s discovery of the beeway. 150 years is a short time-span only when compared with the success of the skep which had been in use for 2,000 years at least. Beekeeping in modern hives also started anew by experimentation. Alas, it often exploited the advantages of api-technology and ignored centuries of experiences which skep beekeeping had given the old folk. Beekeepers who were successful in their climate then spread the gospel of their experiences far and wide, the authors scarcely paying attention to regional differences of climate and environment.
ln some areas the old, canny folk were slow to change their ways. The beekeepers of old had known all the time that a certain size of hive was ‘best’ for certain conditions. Even Pettigrew (mainly credited with advocating very large skeps) pointed out, when read properly rather than quoted indiscriminately, that skeps had to be of different capacities to suit early prime swarms of great size and the small casts which emerged last. (lt is strange that we quote him frequently for his insight when we want to advocate the larger hive, yet ignore his prejudicial attitude towards the profitability of wooden hives. l am sure he would have approved of polystyrene hives as a substitute for polySTRAWene hives). We now stress ‘standardisation’ for efficiency’s sake and we suggest to use one hive for all sizes of colonies. Only for increase and queen rearing do we use small nuclei for frames of standard dimensions, though most beekeepers are aware that wintering of nucleus stocks is risky business.
But the bee still ‘knows its buzziness bezzt’ and an old friend had been convinced that bees possessed a ‘sixth sense’ for cavity size. Since then, an American scientist has provided us with the proof of the correctness of the theory. As part of his studies he offered stray or wild swarms the choice of many bait hives. His simple boxes were of three sizes; small, medium and large. The medium sized box of ply was just about the size ofa National brood box or a Langstroth one. And this was the size which in his experiments was preferred by most swarms. He fur-
ther was able to show that when scouts were looking for new homes they were investigating internal clearances by walking, hopping and letting themselves drop. In fact, they were ‘measuring’ size and capacity. Returning home they recruited other scouts to come and look at their find. When a ‘sixth sense’ is so deeply embedded in the genetic memory of a species, then it must have been ’learned’ during the struggle for survival and must have considerable survival value. We would be foolish to ignore what the bees are trying to tell us! i
Hive size (in winter) must therefore have an important bearing on survival, although, in summer, it must also be a factor contributing to successful reproduction by swarming. Of course, reproduction must also occur at the time when the survival of the species is optimised. We, the selfish beekeepers, are between the devil and the deep blue sea because our interests do not coincide with those of the honeybee – as a species. For the latter ’beekeeper’ (the bee itself) the cavity must be adequate to hold winter stores for survival until the next flows provide adequate, that means surplus, nourishment. That the space must also be small enough for swarms to issue at that time when they have the best chances is of greatest importance for reproduction.
Too large a cavity in spring and summer and the swarm may leave home too late to survive in a bad year. In that case, the parent stock also struggles to overcome the loss of queen and bees before winter sets in. Too large a cavity in winter and the winter cluster will not benefit at all from the small amount of heat lost from its surface. Although every degree counts as far as bees are concerned, the air in the very large cavity will not be modified by one iota. Maybe we have followed American convictions far too long when we quote the opinion that the bee does
not heat unoccupied space. Yet, while this is true as far as the conscious effort by the bee is concerned, it does not mean that a minute rise in hive temperature, through loss of heat to the immediate surroundings, is of no benefit at all to the cluster. Newest work on wintering in Canada’s prairies proves the point.
ln nature, thick walls of hollow trees gave more protection, and overall heat losses were smaller in the smaller, therefore warmer space. Further protection was afforded to the colony when it fastened its combs to the roof of the cavity and filled the combs above their heads with honey reserves. The beeway between combs and the closed cavity avoided through ventilation. Passages between combs were wider where brood had been reared last and where food had been consumed and here was no barrier against the escape of the waste gases of combustion, of heat generation to keep the cluster warm. The natural tendency for ventilation of gases, including water vapour, was downwards: bees were as warm as a bug in a rug. Few bees faced the coldest temperatures as most bees of the cluster were where warmth had not escaped and here they saved their energies to stay alive.
On the other hand, when heat losses cannot hope to warm a large cavity in a thinwalled hive in the slightest, then temperatures within the hive can drop to those of the outside. Temperature losses from the winter cluster can be made worse by ‘through ventilation’ and only too often this has been the practice in the recent past. ln severe climates, the combs near the cluster are at freezing point, and condensation, even frost, can form wherever dew point is reached. Later, when warmer temperatures occur, such moisture will take a long time and much energy
to dry out. On the other hand, condensation will occur further away from the bees, nearer the hive walls, wherever the slightest warmth is retained and not lost. ln that case little or no condensation occurs except far away from the bees.
The Bees’ Activity of Fanning
How often do we read about the need for top ventilation as the answer to all problems? It is supposed to be essential to let the moisture get away from wintering clusters and out of the hive, it is said to be important in summer to ease the work of evaporating the water content from ripening nectar more efficiently. Many of the arguments given to back up any recommendations for providing more and more top-ventilation are based on reasoned considerations or anthropomorphic thinking rather than on a sharp-eyed observations of bee behaviour. For those who observe behaviour without preconceived ideas it is obvious that the bee has arranged its home to suit its own experiences within the constructed set of combs and the chosen home. Bees therefore have developed behaviour patterns to cope with living, brooding and surviving among the multi-comb structures of waxen cells. Fanning answers problems of rising levels of CO2, humidity and heat.
The activity of fanning was investigated at Craibstone during the latter part of summer 1987. An observation hive holding two frames of Dadant dimensions with a total comb area of 16,500 worker cells. In one bottom corner, the hive has a 30 mm diameter entrance attached to a perforated plastic tube for egress and access through a window. During the height of the generally poor, cold and unproductive summer the colony had grown strong, yet very few bees could be seen fanning. Diffusion seemed to cope with elimination of waste gases. Fanning only
started on comb as soon as heavy feeding began in order to build up sealed stores for winter. Bees seemed to fan by vibrating their wings only where they had room to spread and beat their wings without hindrance. No fanning could be observed where a beeway only was left between the inner layer of glazing and sealed cells containing honey. When other bees made contact with the wings of fanning bees the fanners usually ceased beating their wings on that side. Occasionally fanning stopped altogether after contact. Other bees, after making one-sided contact with a passing bee, turned slightly and carried on fanning. Most bees connected the hind wing to the front one, but some bees in a tighter corner used the forewing only for fanning, while the hind wing simply vibrated ‘in sympathy.
Each set of observations was made over a period of several minutes. The face of the comb was scanned systematically and each fanning bee was recorded by an arrow, the tip representing the head. After half an hour the observations were repeated and new arrows were drawn into the same diagram. lt is therefore possi-
ble that some fanning bees are recorded twice if they remained in the same spot. For easier assessment, all arrows were sorted into 12 directions of the compass, each varying by 300 from the next. Analysis of the directivity of fanning showed that very few bees were fanning while standing ‘on their head’ (driving air upwards). Most bees took up a vertical, hanging position or slightly askew from the vertical. This position was assumed to be affected by gravity acting on the bee and, in the absence of a better explanation, the three categories of vertical (hanging), and 300 on either side, were lumped together as gravity-oriented fanning.
The next numerous group of fanners fell into the group with horizontal and nearhorizontal positions (300 up or down from horizontal). Among these fanners a distinct directional bias was discovered. The majority of fanning in horizontal and near-horizontal direction appeared entrance-oriented. This entrance-oriented group was significantly larger than bees fanning in the opposite direction, their heads pointing towards the entrance. The ‘horizontals’ were represented in greater numbers at floor level and the where the top and side bars of wooden frames left a larger-than-beeway passage between glass and substrate. It is difficult to find an explanation or consistent pattern for it. In some instances two bees fanning in opposite directions were facing each other, while at other times the bees stood tail to tail.
When the observation hive was turned upside-down so that the entrance, the only opening, was above the brood nest, the bees showed little disturbance and adjusted quickly to these new arrangements. On the whole, the trend of fanning remained as before, with 55 bees fanning in vertical or near-vertical positions, and a larger number, 58 bees, were entrance-oriented while in horizontal and nearhorizontal attitude. Although the hive was now upside down very few bees were standing ‘on their head’ (3) and fewer bees than before opposed the entrance oriented group of horizontal and near-horizontal fanners.
Direction of fanning could be triggered by a number of stimuli or perceptions. Gravity has already been mentioned, and the quick return to normal, upright fanning by bees in the brood nest appears to support this decided preference (the entrance is above their headsl). The entrance-oriented horizontal bias can either be explained by a ‘knowledge’ of the geography of the hive (whether right way up or upside down) or a pressure gradient. A pressure gradient (or partial pressure gradient of humidity or noxious gases) giving rise to perception of ‘least resistance’ ,
could be another factor in the choice of directional fanning. The perception of air flow as a directional stimulus is a third possibility and this effect could possibly be the explanation for the concerted fanning in the wider passages under the frames and in the entrance tube. Here the variation of directions was small. Wherever the wood of top bars created a wider gap which the bees had been unable to narrow down, and also in the gap below the bottom frame and the floor of the hive, the bees stood in greater numbers and were fanning with more pronounced direc-
tionality. On the floor of the hive most bees stood diagonally to the central line, fanning towards entrance in the shallow (22 mm deep) and narrow (single frame, 40 mm wide) passage below the frame.
ln the tube leading to the outside, all traffic leaving the hive was travelling along the outward-bound air stream, with several more bees fanning on that same side within the tube to boost it on its way. Outward»bound traffic clung to the left and upper side of the plastic tube, while incoming bees with a heavy tummy crawled along the floor and on the right side. This pattern of organised traffic was observable at the entrance, where bees with pollen loads landed and entered on the left, while the stream of foragers leaving for the fields emerged on the right. In such wider and unobstructed passages the seemingly ‘organised’ traffic may well be air-flow oriented. Between passages of brood comb any definite preference cannot be detected as easily and numerous observations must be made to discover a trend.
On the other hand, when the hive was up-ended many bees on an area of empty comb near the entrance, a patch usually crowded with waiting and dancing foragers, suddenly became mainly flow or entrance-oriented rather than fanning vertically (hanging). Suddenly the space above the brood had lost the protection of the beeway, and warm air (with waste gases and humidity) was lost in the now upward direction. Bees joined in along the line of flow.
The up-ended condition did not seem to affect the colony. lt was left for a few days in its topsy-turvy position. Although the queen could not be found for several hours afterwards, when seen again two days later, she carried on laying eggs as before. She now slewed her body around after lowering her abdomen into the cell. She had approached most cells while in the near-vertical position, and changed her foot-hold to get into a near-horizontal position before laying the -egg.
(’Somersaulting’ hives and skeps was advocated at one time as a method of swarm control or a means of slowing down brood production, but the observations show that the queen can carry on as normal – at least after a while.)
Table 1. Number of fanners counted during 8 periods of observations: 5 in
normal position, 3 in up-ended position
Normal Hive Up-ended
Hive Total No
1) Fanning gravitationally: 136 55 191
2) Anti-gravitationally: 9 3 12
3) Horizontal and near-horizontal
(a) Entrance oriented:
i) on brood comb: 16 ll 27
ii) on side bars and top bars: 62 21 83
(b) Fanning away from the
i) on brood comb: 16 4 20
ii) on side bars and top bars: 9 3 12
4) Fanning on floor:
(entrance oriented only) 110 56
These figures, (especially categories 1, 2, and 3,a,i) prove fairly conclusively that bees, over the millions of years, have organised their ‘home’ for bottom ventilation. Even up-ending the brood nest could not alter the fact. Swarms usually settle at the top ofa cavity, then start their comb building from the ‘ceiling’ , extending them vertically downwards. Bottom ventilation is obviously the natural trend, and ‘top ventilation’ is alien to them. In man-made hives we have created manmade problems and these need man-made solutions at times.