Do Bees Hibernate ?

Think Of The Winter Bee Cluster As A Swarm….Just One With A Box Around It.
A Swarm Of Bees Is Just A Naked Cluster Of Bees

Between New Year and Easter, the question which I am most frequently asked is : “Do Bees Hibernate?

The short answer is that they form a cluster, a gently dynamic, oval mass in the middle of the brood box, dropping their metabolic rate by a couple of notches. But the full answer to the question is a little more complicated than that.

It all depends on what you mean by “hibernate”. Insects are cold-blooded and bees are no different. However, honeybees fall into the small minority of insects which can generate their own heat, like mammals, through muscular exertion (human beings do this by shivering, for example). So let’s see where we can check the box on bees having a regular “hibernation“: seasonal cycle, Yes, metabolism slows down, Yes, own thermoregulation, Yes.

But if by “hibernation” you mean a state of suspended animation, like a bear or a bat, or a comatose Rip Van Winkle interlude, snoozing unrelentingly thorough 3 months of oblivion, then “No”, bees don’t hibernate like that.

As winter takes hold, bees form their cluster. Composed of some 10,000+ winter bees (late-born in the previous Autumn and physiologically endowed with a body able to store fat), it expands and contracts, according to the exterior temperature.  Food consumption drops as long as the bees remain in this torpid state. But in warm spells, the cluster will relax, with some bees even leaving the hive to make “voiding flights” and dedicated mortuary bees removing dead bees from the hive.

But the cluster will huddle protectively tight to conserve heat as the temperature drops. The grim fact is that, if the thorax of a bee (where the wings are located, between the bees’ head and the abdomen) falls to a temperature a few degree below 10C, a bee will fall into a “chill coma” which renders it rigid, motionless and unable to vibrate its wing muscles to create the heat required for its cold-blooded body to stay alive.

Honeybees overwinter as a reduced colony, a living, slow-motion family unit with the Queen at the centre, unlike wasps or most other bees, where fertile queens shelter alone. This behaviour illustrates why scientists have described colonies of bees as “superorganisms” in which each individual bee is only a component part of the greater whole. The concept of a colony of bees as a single social civilisation is key to my beekeeping.

Let’s take a closer look at the cluster: the outer mantle of bees is like a string vest, insulating the soft body of this concentration of bees. These wrapper bees will eventually rotate their positions with warmer bees, bubbling up from the heated community of the cluster. In temperature terms, this outside layer will be at around 10-15C, with the main body of bees at 22-24C and new brood at the centre requiring a temperature of 33-35C. That means that the part of the hive where the bees cluster will be almost as warm as a centrally-heated home in winter, the main mass of bees overwinter at the same temperature as a balmy summer’s day, while the brood area as hot as a Caribbean holiday – even when the weather is freezing outside !

So my answer to the question “”Do Bees Hibernate?” is an unsatisfactory one. They sort of do, but they kind of don’t. But I was excited to stumble across one insight as I was thinking this article through.

The cluster is hard to see, buried deep inside a winter beehive and divided by brood frames, so my challenge was: how can I help people visualize a cluster? Then it came to me: take a look at the photo at the top of the page.

Here you can actually see the egg-shaped formation and mantle of outer bees typical of a cluster. But this is a swarm of bees, settled on a branch.

It really made my day when I realised that a swarm of bees is just a naked cluster !


Bees CloseUp_edited-1
Top-Down View Into A Cluster – Dark Seams Full Of Winter Bees

Three times last week, it happened. That’s a record. Once walking the dog in the rain, once while reviewing a CV for a client and once when pouring white wine for Sarah’s friends: the question on everybody’s lips was : “What Do Bees Do In Winter ?

Well, for starters, they don’t hibernate. Not in the sense that they curl up for a 3-month metabolic nap and lose half their body mass in the process, although, looking at a beehive on a frosty morning, that might seem a credible proposition.

We are warm-blooded creatures. Unlike bees, which are cold-blooded, we do not fall into a bottomless “chill coma” if the temperature drops below 10°C. So in winter, the bees adopt a communal strategy to avoid this outcome and form a cluster for survival. It is almost as if this reflex was just another stage in the bee lifecycle: egg, larva, pupa, bee, cluster.

So during extended cold periods, you can visualize honeybees drawing themselves together into the shape of a rugby ball (not unlike a settling swarm). In my mind’s eye, I’m seeing a small nation of bees, huddled between the frames in a hive over winter. I playfully call it “hivernation”. (OK, so it’s the French word for hibernation, but in English it crackles with connotations, which at least steer us away from the popular misconception of honeybee “hibernation”).

Our comprehension of the finer thermodynamics of the bee-cluster is imperfect, but the big picture is undisputed: the bees in the cluster vibrate their flight muscles while keeping their wings still, thereby raising their body temperatures, like a shiver. With thousands of bees “shivering” constantly, this warmth-creation in the broodnest, at centre of the cluster, packs out a temperature around 35°C, which is more or less our own human body temperature. That compares to a toasty thermostat setting of over 20°C required for the Queen’s survival and a risky, fuel-allowance-level of 10-15°C  for the insulating perimeter of the cluster. But be reassured. Intense outside cold is manageable – beekeepers in Finland will tell you that bees do not die from cold, given a proximate food source and adequate shelter. On the other hand, excessive humidity, heavy varroa loads, an outbreak of nosema or starvation can kill a colony.

The winter bee-cluster provides the key to unlock a second, more fundamental two-legged misconception about bees. Consider: we humans are fiercely proud of our individuality. We celebrate it in our choice of words, our clothes, our loves, our tattoos (or indeed, lack of the same). When we are in a crowd, we still profess our own identity and self-determination (consider the 37,000 runners in the London Marathon!). We can be inside a crowd, but we are not the crowd: we are, all the time, our own selves within that crowd.

Not so with bees. To our eyes, any single bee may appear to be an individual unit because of the imposition of our own insistence on uniqueness onto bees. But that is our error. In reality, that individual bee is always part of a higher organism: the bee colony. Think of it like this. Each bee is a solitary drop in the bee-bucket. The cluster illustrates this perfectly: the welfare of the colony is paramount, the outcome for each component is trivial. The bees aren’t just in a cluster – they are the cluster.

So what happens inside the cluster, when it’s at home? Well, it’s a slow-motion microcosm of the normal bee-world: a brood area in the middle, along with the Queen, surrounded by the winter bees. When those worker bees on the outer edge of the cluster become cold, they knead themselves towards the warm centre of the group to recover, and, dynamically, other bees will pulse up to the surface, taking their turn to shield the group from the winter chill. It may be that, in warmer interludes, the cluster will move to the honey stores, or move the honey from the comb to the cluster. But over an average winter, a colony will need some 30lbs of honey as fuel to burn at its economical, night-storage rate of activity. For beekeepers, “hefting” or weighing the hives is the best way to gauge whether the bees are light on stores and need an emergency food-parcel of sticky, white baker’s fondant (inverted sugar) onto the top of the cluster. Importantly, this has to be placed in direct contact with the cluster – it is an astonishing reality that bees will perish from starvation, torpid heads down in the empty food cells, just millimetres from ample energy reserves, rather than break the cluster in cold winter months.

And then there’s the inconvenient question – if the bees spend all winter eating honey and “shivering”, when do they get what our coy American cousins call a “comfort break” ? Well, a bee’s rectum expands to accommodate the waste material over the winter months and on the first warm day of spring, bees break the cluster. Chipped away from the block, a bee may leave the hive on a “cleansing flight” to jettison that accumulated waste. And so the bees appear again to us, popping out of the hive one by one, as solitary tokens of springtime. But what the cluster has taught us is that the colony itself is the organism. Then we can see each bee for what it is: a single strand in the weave of the colony’s fabric.

Time to get back to the mundane practicalities of existence: it is generally agreed amongst higher life-forms that it is best not to put your washing out to dry on the line on that very first fine, warm afternoon of the year! For obvious reasons…..