Good wintering starts now

People usually think about wintering when it is already too late, that is in November, at the first cold, when you lift the roof and reckon whether the bees will make it. In fact whether a colony winters is decided in summer and early autumn. Winter merely presents the bill for what you did, or failed to do, in August and September. So if you are reading this in the second half of summer, this is exactly the moment to deal with wintering, not to put it off.

This article is a practical list of what makes wintering succeed, in the order I actually deal with it. I will let you in on it straight away: the most important thing is not what gets talked about loudest, that is sugar. The most important thing is a healthy winter bee with a proper fat body, and that ties to two things: to varroa and to pollen.

Step one: varroa, before the winter bee is born

The winter bee differs from the summer bee. It lives not six weeks but several months, carries the colony to spring and starts the first brood. It is raised in August and September, and with today's warm autumns even in October.

If this generation emerges weakened by varroa and burdened with viruses, no feeding or insulation will fix it. That is why the first step to good wintering is not syrup or wrapping up, but dealing with the mite before the winter bee is born. How and when, I covered separately under varroa treatment. Here the rule is enough: varroa first, then the rest. The order matters, because feeding a sick colony is pouring sugar down the drain.

Step two: pollen, bee bread and the fat body, the real foundation

And here we come to the thing that gets talked about far too rarely, and that decides everything. It is not sugar that makes the winter bee, but protein. The winter bee is an insect with a well-developed fat body and a high level of vitellogenin, the protein store that in a bee serves as reserve, immune support and fuel for spring larval feeding. A colony that enters winter with bees whose fat body is well developed will winter through almost anything. A colony with protein-starved bees will not winter even a mild season, though it had sugar to the brim.

The fat body is built from pollen and bee bread. Young bees of late summer and early autumn must have access to abundant pollen to lay down that reserve. If pollen is short in that period, you get a protein-poor winter generation, and this is the quiet cause of many collapses later blamed on frost or varroa. So in autumn I make sure the colony has a bee bread reserve in the nest. I do not strip the nest of pollen, and if the season is lean in that respect, I support the colonies with a protein feed. A side curiosity: goldenrod, whose honey is troublesome for winter, gives at the same time excellent, abundant pollen, so as a protein source for the winter bee it is priceless.

There is one more mechanism here that links wintering with the fight against varroa, and few connect it. Whether a bee becomes a short-lived summer bee or a long-lived winter bee depends largely on whether it worked as a nurse. A bee that heavily feeds brood spends its fat body producing royal jelly and becomes short-lived. A bee with no one to feed, because there is little brood, keeps its fat body and passes into the long-lived form. That is why the natural tapering of brood in autumn favours the making of a good winter bee. And here queen caging returns once more: an artificial brood break not only stifles varroa but also relieves the young bees of nursing, letting them keep their fat body and enter winter as full-value winter bees. One tool, two benefits.

Step three: energy stores, how much

Only once you have a healthy, protein-fed bee does thinking about sugar make sense. The colony must enter winter with solid energy stores, roughly the mid-teens of kilograms, but you match the exact amount to colony strength and hive type.

My rule is simple: better too much than too little. Starvation in winter is the stupidest way to lose a colony, and surplus stores are not lost. If in spring unused stores remain in the nest, you simply withdraw those combs and use them to boost splits or weaker colonies in the new season. Stores in a good comb are ready capital for the start, so there is no reason to skimp in autumn for fear of waste.

Step four: which sugar and how to give it

Both white sugar and ready invert syrup are suitable for wintering. Colonies winter well on both. But do not confuse winter syrup with thin 1:1 syrup: the thin one serves to stimulate the queen to lay, in spring and during a summer nectar dearth, not for wintering. You give the winter store thick, so the bee has little water to evaporate and seals it quickly.

A word on stimulation while we are here, because it is easy to oversimplify the wrong way. If a nectar dearth falls in the second half of summer and the queen throttles back her laying in response to the lack of nectar, you should stimulate the colony with thin syrup so she lays abundantly from roughly mid-July to the end of August. This is precisely the window in which the winter generation is made, so if the queen slows down then, you will be left short of winter bees, and neither pollen nor a heavy store will make that up afterward. Thin syrup keeps the laying going, while pollen decides the quality of those bees, and one without the other will not work. Only after this window, at the turn of August and September, do you switch mode and flood the nest with thick winter stores.

There is one hard condition here though: you stimulate with sugar only after the marketable honey is off. As long as supers are on the hive or the store could reach honey for sale, you do not give syrup, because it adulterates the honey. In short, stimulating during a dearth after the last harvest is entirely in order, and inadmissible while you are still taking honey.

Now the matter of acidifying, because a lot of confusion circulates here. Lightly acidifying the feed is helpful, because it brings it closer to the naturally acidic reaction of nectar and is gentler on the bee's gut. But there is one condition whose breaking turns help into poison: do not cook sugar with acid. Breaking sucrose down with acid at high temperature produces HMF, hydroxymethylfurfural, which is toxic to bees and especially dangerous to the long-lived winter bee, because it acts more strongly the longer the insect takes it in. The research agrees: sucrose broken down with acid under heat is harmful, unlike sucrose broken down enzymatically. The conclusion is simple. Want to lightly acidify the feed, do it cold and in moderation. Want inverted sugar, buy enzymatic invert rather than inverting it yourself with acid on the stove.

How much to give and which invert to choose

While we are on sugar, two practical matters: how much to give and how the inverts on the market differ.

How much. The conversion is simple. Take it that one kilogram of sugar, dissolved and stored, gives roughly one kilogram of store, though the bee spends a little sugar on the processing itself, so give a slight surplus. A litre of ready invert is roughly the equivalent of one kilogram of sugar, because such syrup is about 72 to 75 percent sugar. So if you are aiming for the mid-teens of kilograms of winter store per colony, you need roughly the same number of kilograms of sugar as thick syrup, that is the classic three parts sugar to two parts water, or roughly the same number of litres of ready invert. Below ten degrees the bee will not take liquid feed anyway, so in an emergency you are left with candy or fondant over the cluster.

Which invert. And here is a thing rarely mentioned that matters: inverts are not all equal, because what they are made from differs. The best for winter is a sucrose-based invert, that is one made enzymatically from beet or cane sugar. It contains only sugars the bee fully digests, glucose, fructose and residual sucrose, has low HMF and does not crystallise in the comb. A worse choice, though often cheaper, are starch-based inverts, made from corn or wheat, that is glucose-fructose syrups. They contain maltose and complex oligosaccharides that the bee digests with difficulty or not at all, which burdens the gut and encourages dysentery over a long winter, and on top of that they crystallise more readily in the cells, leaving the colony with stores it cannot reach. A simple rule: for winter choose sucrose-based invert, not starch-based, and if in doubt, plain white sugar is always safe.

This leads straight to two myths worth busting.

Myth one: you have to invert sugar yourself, because the bee cannot digest sucrose. Untrue. The bee has its own enzyme, invertase, and breaks sucrose down with ease, as it does with every nectar. You do not need to do it for her, and certainly not with acid under heat, because that only produces HMF. Plain white-sugar syrup is entirely fine.

Myth two: invert is healthier and better for winter than plain sugar. That is mostly marketing. Controlled studies found no advantage for colonies wintered on sucrose-based invert over those wintered on plain sucrose, and invert is more expensive. Its real advantages are practical, not health-related: it is ready to use and does not crystallise, which matters for late, cold feeding and for crystallising flows like goldenrod. There is one caveat, and you already know it: this holds for sucrose-based invert, because a starch-based one can actually worsen wintering.

Herbs in the feed, the old school with sense

Adding herbs to the winter feed is a practice with a long tradition, and this one has a rational core. The classic is an infusion of oak leaves or bark, rich in tannins, which are astringent to the gut and have for generations been regarded as help against dysentery and nosema. Beekeepers also use tansy, greater celandine, wormwood or yarrow, credited with antiparasitic and gut-supporting action. The scientific confirmation of some of these herbs is modest and comes mainly from work on oils such as thymol or carvacrol, which really can support infected bees. I treat herbs as a sensible, cheap supporting addition, given in moderation, not as a medicine. The key word is moderation, because even a good oil given to healthy bees in excess can harm.

Late flows: goldenrod and heather

A separate case where the economics can mislead. Honey from goldenrod and heather crystallises quickly in the comb, and crystallised stores the bees cannot use in winter, so the colony can starve on a full comb. Heather is additionally jelly-like and hard to extract. On top of that the late flow coincides with the cold, in which the bee poorly processes and evaporates ordinary syrup.

That is why with late flows it is often most sensible to take off such honey and spend a few extra on shop invert. You get a store that does not crystallise like goldenrod, is safe as far as HMF is concerned because it is enzymatically inverted, and which the bees store without processing, even though it is already turning cold. It is one of those outlays that pays back in wintered colonies.

Once you move on to the winter store, feed briskly and fairly early, so the bee has time to store and seal it before the cold. But more importantly, flooding the nest with thick stores has another, often underrated job: filled combs limit the queen's laying space and help shut down late brood. And that is exactly the point at this stage, because young bees that no longer have to feed larvae keep their fat body and pass into the winter form, while the colony enters winter without needless late brood in which varroa would breed anyway. So the thick end-of-season store is not only a larder but also a tool for closing down brood rearing at the right moment.

Colony strength and the nest, in which we bust a myth

Strong colonies winter better, because they have a better ratio of bees to the area they maintain. In autumn it is usually better to unite two weak colonies into one solid one than to hope both somehow survive. Sentiment costs losses here.

But I have to bust a myth, because it is repeated like a mantra: that the nest must be matched exactly to colony strength, comb for comb. Yes, a tight nest has its advantages, but it is not the life-or-death matter it is painted as. In nature bees winter in tree cavities that are rarely a perfect fit, and they manage, though not always in the most optimal conditions. A little more space is not a death sentence. Interestingly, in a tighter nest carbon dioxide builds up more easily, which the bees tolerate well and which actually helps them winter calmly by lowering their activity. So the thing that really decides is not perfect narrowing, but something else: ventilation and moisture management.

Moisture, what really kills, and a lesson from nature

Let me start with a correction, because a lot of half-truths circulate on this topic, including ones I repeated earlier myself. In winter bees are not killed by moisture as such. The bee evolved in a humid tree cavity and tolerates high humidity well, and even needs it. What kills it is something else: cold water condensing on the roof and dripping straight onto the cluster. A wet bee loses the insulation of its hairs and cannot hold heat. So it is not about driving all the vapour out of the hive, but about keeping condensed water off the bees.

It is worth seeing how nature solved this, because it works differently from what you often hear. A tree cavity has thick walls of high heat capacity that keep the interior warmer and more stable. Warm, humid air from above the cluster rises, and where it meets the cooler side walls it condenses and runs down them, away from the bees, rather than dripping on the cluster. On top of that the cavity usually has a single small entrance at the bottom and no top ventilation, so heat and humidity largely stay inside, which suits the bees.

And now the correction I fell for myself: the propolis lining of a cavity does not carry moisture outward, quite the opposite. Propolis is a resin with very low permeability to water vapour, so in practice a waterproof layer, a barrier to moisture. The bees line the walls with it not to let vapour out, but to seal cracks, protect the wood from rot and fungi and cut out draughts. The role of humidity buffer is played rather by the comb itself, especially old brood comb with cocoons, which is hygroscopic and evens out swings in humidity.

A hive does not have all this so well arranged. It has thin walls and a crownboard that chill quickly, so vapour condenses on the cold ceiling and drips straight down onto the cluster. That is the killer. And that is where the two schools come from, which I write about below: either you carry the vapour off by ventilation, or you heavily insulate the top so the ceiling stays warm and condensate forms on the walls and runs down rather than dripping on the bees. Both routes have one goal: to stop water falling on the cluster. What you must certainly not do is shut the colony in a cold, sealed box with neither of these solutions, because then you get the worst combination, a cold ceiling and condensate straight on the bees.

How the cluster really works, a few facts

Understanding what happens in the cluster changes how you run wintering. A few things worth knowing.

Bees do not hibernate, they heat. Unlike most insects, bees do not fall into torpor in winter. They crowd into a cluster and actively produce heat, vibrating their flight muscles without moving them, that is shivering. The heat is generated mainly by the bees in the core. That means the colony works and burns stores all winter, it does not sleep.

A warm core, a mantle on the edge. The cluster has two layers. The outer mantle is packed so tightly that the bees' hairs interlace into an insulating layer, and its temperature holds just above the torpor threshold, around 8 to 10 degrees. The core is much warmer: broodless about 20 degrees, and once brood appears as much as 34 to 35 degrees, held with pharmacy precision. Bees from the cool mantle and the warm core constantly swap places.

The cluster travels upward. As the bees eat the store, the cluster moves as one body, usually up and to the side, following the warmth and the store. That is why the store should be above the cluster and around it, not off to one side of the hive, because there the bees will not reach it in frost.

Starvation on a full comb, or isolation starvation. This is one of the most treacherous things in wintering. In hard frost the cluster will not break to cross an empty comb to reach a store lying a few centimetres away. A colony can starve with several kilograms of honey in the hive, only not where it happens to be sitting. That is why the arrangement of the store around the cluster matters as much as its quantity.

The danger is not midwinter, but late winter. Contrary to intuition, a colony consumes the least store in midwinter, when it is broodless and calm. Consumption shoots up only in late winter and early spring, when the queen starts brood, because the core must then be held at 34 degrees. That is why most colonies starve not in January but in February and March, often just before the first flow. Checking stores in late winter saves more colonies than autumn feeding.

The cleansing flight. A bee does not relieve itself in the hive in winter. It holds its faeces in a distended rectum for weeks, waiting for a warmer day, around ten degrees, to fly out and cleanse. If the store is hard to digest, for instance honeydew, the gut fills faster and dysentery in the hive threatens before a chance to fly comes. This closes the thread on clean stores: it is not only about energy, but about the bee lasting to the cleansing flight without an overfull gut.

Protection against intruders

In late autumn, when the bee settles into the cluster and defends the entrance more weakly, guests come to the hive. Mice can enter through the entrance, nest in the warmth, eat store and bees and wreck combs. Mouse guards or entrance reducers go on before it turns cold, because a mouse once let in does huge damage. Besides, the hive should stand stable, with a roof that does not leak, sheltered from the prevailing wind, and the entrance set so it does not blow straight into the nest and so the bees can take a cleansing flight on a warmer day.

A last look before winter

Before you leave the apiary in peace, do a final round without taking nests apart: check the hives stand stable, the roofs hold, the entrances are protected, nothing leaks. In autumn less is more, because every needless opening chills the colony.

And the last thing, in the spirit of this whole series: do not act from the calendar, but from observation. A strong colony, healthy, with a well protein-fed bee, good stores and a dry nest, will winter almost regardless of what winter comes.

Curiosities and controversies

The cluster is not a duvet, but a radiator. For a hundred years it was repeated that the outer layer of the cluster insulates its core. Derek Mitchell's 2023 research turned this on its head: the cluster's mantle behaves not like insulation but like a radiator carrying heat outward. What is more, a thin-walled hive loses four to seven times more heat than a tree cavity, and clustering itself may be not the bee's nature but a response to the thermal stress we inflict with a poor hive. In other words, many behaviours we took for innate may only be coping with our equipment.

Top ventilation or insulation: a war of two schools. This follows directly from the above and nuances some classic advice, including what appeared here. The traditional school says: ventilate at the top to remove moisture. The insulation school, following Mitchell, replies: heavy top insulation and no top vent give an interior warm and humid like a tree cavity, where vapour condenses on the walls and runs down rather than dripping on the cluster. Both schools want the same thing, a dry cluster with no condensate on the bees, but reach it by two different routes. The truth depends on your hive and climate, but it is worth knowing the topic is not closed.

The goldenrod paradox. The same plant that gives troublesome, quickly crystallising honey is at the same time one of the best late sources of pollen. For the winter store goldenrod is an enemy, for the fat body of the winter bee it is an ally. A good lesson that in beekeeping something is rarely simply good or bad.

Sugar can be healthier for winter than honey. It sounds like heresy, but it makes sense. Honey, especially honeydew, heather or goldenrod, is rich in residues indigestible to bees, which burden the gut over a long winter without a cleansing flight and encourage dysentery and nosema. Clean sugar stores leave far fewer such residues. So for the naturalist wintering on honey is obvious, and from the winter bee's gut point of view clean sugar is simply safer.

Bees do not heat the hive. They do not try to warm the whole interior, only the cluster itself, whose outer shell can be surprisingly cool. That is why the empty space around is not as dangerous as it is painted, and what truly matters is one thing: that water does not drip on the cluster.

The cluster survives unthinkable cold. In one experiment clustered colonies survived over a dozen hours at minus eighty degrees. A single bee would die in minutes, but the cluster as an organism can do things the sum of bees cannot. It is the best illustration of the rule that it is the colony that winters, not individual insects.

Race makes a difference. Dark and Carniolan bees winter frugally, in small, early-broodless clusters, using less store. Italians like to keep laying later into autumn and use store for longer, which can leave them worse off in a long, harsh winter. It is no accident, but the result of the climate each race was shaped in.

Snow can be an ally. A hive buried in snow is not a problem, as long as the entrance is not sealed shut. Snow insulates and smooths temperature swings, and bees winter calmly beneath it. Forced clearing and peering in during frost harms more than it helps.

Moisture can be an ally against varroa. Against the rush to dry the hive bone-dry, high humidity in the brood nest limits varroa's reproduction, as Kraus showed back in the 1990s. It is a further argument for fighting dripping water rather than humidity itself, because the latter can play into the bees' hands, and even work against the mite.

Most common mistakes

Focusing on sugar and forgetting pollen. It is protein and the fat body that decide wintering, not sugar alone. A protein-poor winter bee will not winter even on full stores.

Putting everything off to late autumn. A healthy winter bee, a pollen reserve, stored sugar and a dry nest must be ready earlier. In November you can only count losses.

Feeding a sick colony. Syrup poured into a colony devoured by varroa is wasted sugar. Health first, stores second.

Home-inverting sugar with acid under heat. Acid plus high temperature is the road to HMF, which poisons the winter bee. Light cold acidifying is fine, boiling with acid is not. Want invert, buy enzymatic.

Not reacting to a summer nectar dearth. If in July and August the queen throttles back her laying for lack of a flow and you do not stimulate, you will be left short of winter bees. This window decides the strength of the wintering colony.

Stimulating with supers on. Sugar stimulation while marketable honey is still on the hive adulterates the honey. You do it only after the last harvest.

Wintering on crystallised goldenrod or heather. Bees cannot use crystallised stores and may starve on a full comb. Better to take it off and give invert.

A cold, sealed box. Sealing everything up with neither top insulation nor ventilation gives the worst combination: a cold ceiling on which vapour condenses and drips straight onto the cluster. You solve moisture either by ventilation or by top insulation, but do not shut the colony in a wet, cold box.

Stores not above the cluster. In frost the cluster will not cross an empty comb to reach store off to the side of the hive. The colony starves in a full hive. The store belongs above the bees and around them, not on the margins.

Easing off on checks in late winter. Most colonies starve not in January but in February and March, when brood restarts and store consumption shoots up. That is when you check whether there is anything to eat, not tick the job off after autumn feeding.

Liquid syrup in frost. In winter the bee will not process thin feed and will not go far for it. In an emergency you feed with sugar candy or fondant placed straight over the cluster, not syrup.

Sources and further reading

• EFSA (2022). Evaluation of the risks for animal health related to the presence of HMF in feed for honey bees. Reference point for HMF toxicity, with particular attention to the winter bee.

• Work on HMF formation in homemade syrups (effect of temperature and acidity) and on the harm of acid-hydrolysed sucrose, as opposed to enzyme-hydrolysed.

• Amdam G. V., Omholt S. W. Work on vitellogenin and the fat body as the basis of winter bee longevity.

• Seeley T. D. Research on the natural bee nest and the propolis envelope in tree cavities. Background for moisture management.

• Mitchell D. (2023). Honeybee cluster, not insulation but stressful heat sink. Journal of the Royal Society Interface. Basis of the insulation and ventilation debate.

• Comparative studies of wintering on sucrose versus invert (e.g. Animals 2023) and on the quality of wintering syrups. Basis of the notes on invert types and conversions.