Let’s Talk About Torpor In Honeybees

What is torpor in general?

Torpor, is generally scientifically defined as follows;

Torpor, a state of lowered body temperature and metabolic activity assumed by many animals in response to adverse environmental conditions, especially cold and heat. The torpid state may last overnight, as in temperate-zone hummingbirds and some insects and reptiles; or it may last for months, in the case of true hibernation and the winter torpor of many cold-blooded vertebrates.

"Torpor". Encyclopædia Britannica. Encyclopædia Britannica Online.
Encyclopædia Britannica Inc., 2018. Web. 05 Jan. 2018

Basically “torpor” is a physical response to changes in temperature in a number of animals.

We’ve talked about torpor before in a previous article but not quite in as much detail.  Here I’d like to get a bit more specific.

What is torpor in regards to honeybees?

Torpor is not effected identically across the board between mammals, lizards, birds and insects  Unfortunately, all too many times, people will try to apply the understanding of torpor to honey bees as it applies to mammals.  That is to our disadvantage.

In regard to bees, torpor is a point in which the temperature has the effect of causing bees to be unable to sustain an inner temperature that allows bees to stay mobile and active.

I’d like to quote directly from the well respected book, “Honey Bee Democracy” by Dr. Tom Seeley in the description of bee swarm/cluster temperature regulation.  He cites Dr. Bernd Heinrich research in about 1980.

Heinrich discovered many marvelous things about temperature regulation in honeybee swarms, all of which are key to understanding how a swarm prepares to fly to its new home. First, he found that a swarm does indeed precisely control the temperature of the cluster’s core so that it stays at 34– 36 ° C (93– 97 ° F) regardless of the ambient temperature. He also found that a swarm allows the temperature of the cluster’s mantle (outer layer) to vary with the ambient temperature, but that it keeps the mantle temperature above 17 ° C (63 ° F) even if the ambient temperature falls to freezing (0 ° C or 32 ° F). This means that the outermost bees, which are the coolest, keep themselves warm enough to stay active on the swarm. If they were to cool below 15 ° C (59 ° F) they would enter “chill torpor” and easily fall from the swarm. They would also be too cold to warm themselves back up by shivering.

Seeley, Thomas D.. Honeybee Democracy (Kindle Locations 2025-2032). Princeton University Press. Kindle Edition.

I highlighted some pertinent information as to the effect of torpor on honey bees above on the effect of torpor on bees in a cluster.

Bees resist Torpor

In effect, torpor is something honey bee colonies actively work to prevent.  Bees in the cluster work to generate heat that warms not only themselves but is trapped within the cluster by the outermost layer of bees (the “mantle”.  Those bees in the mantle don’t just take it as a given that being exposed to the cold, they must enter torpor.  They will work to retain their own effective body temperature and move to the inside of the cluster to preserve that temperature if possible.  Honey bees actively resist torpor.

…when the ambient temperature falls below 17 ° C, and the mantle bees start to feel too cool, they crowd inward, causing the swarm cluster to shrink, its porosity to decrease, and its heat loss to diminish (figs. 7.2 and 7.3). In this way the mantle bees skillfully trap inside the swarm cluster the metabolic heat generated by the thousands of resting, immobile bees, and they also keep themselves sufficiently warm. It is only when the air temperature falls below about 10 ° C (50 ° F) that the mantle bees must take the extra step of raising their metabolic rate by shivering.

Seeley, Thomas D.. Honeybee Democracy (Kindle Locations 2037-2041). Princeton University Press. Kindle Edition.

Honey bees have figured out how to maintain over the Winter


Thus Heinrich discovered that the bees in a honeybee swarm have an effective means of conserving their energy reserves. The mantle bees, those most exposed to low temperatures, minimize their need for active metabolism by doing two things when the air becomes cool: (1) letting their body temperatures drop to just above the chill-torpor temperature rather than working to maintain a higher body temperature, and (2) keeping their body temperatures above the chill-torpor temperature mainly by huddling rather than shivering. Of course, these energy conservation measures mean that most of the time the outermost bees in a swarm are too cold to fly, something that is easily demonstrated by skimming a spoonful of mantle bees from a swarm and shaking them into the air. The bees tumble to the ground rather than fly away. So before a swarm can take off to fly to its new home, the cool bees in the mantle must warm their flight muscles to the flight-ready temperature of 35 ° C. And not just in theory! When Heinrich made continuous recordings of the temperatures at various locations in a swarm cluster from when the bees settled to when they departed, he found that during the last hour or so before takeoff, the temperature in the mantle did indeed rise to match the 35 ° C of the core.

Seeley, Thomas D.. Honeybee Democracy (Kindle Locations 2045-2050). Princeton University Press. Kindle Edition.

Again, I’ve highlighted pertinent text that affirms that honey bees avoid or resist torpor because for honey bees, it does not have the same effect as it does in mammals.  Topor in mammals is beneficial to their survival for short term temperature changes in conserving heat and energy.  For mammals. It’s a short term solution whereas hibernation is for long term survival in extreme changes of temperature.

Not so for bees.  For bees, torpor is a state that can lead to death due to failure to maintain just enough self generated heat.

How is torpor important in honey bee colony management?

For many apiculturists, Winter is a nervous time.  We try to send bees into Winter with plenty of stores to sustain energy specifically so that they can continue to generate enough heat to prevent torpor.

We also use mechanical, environmental and other methods to make the hive more efficient in heat retention.  By making hives more heat efficient, we allow bees to expend less energy to maintain sustainable temperatures in the cluster.  Conserving energy also helps the colony to retain their food stores for a longer period of time, preventing starvation.

Causes for concern in beekeepers

In recent years, we have seen an increase in concern and interest in methods being used to check the conditions of over-wintering colonies.  Unfortunately in many articles and videos torpor and it’s effect on bee colonies is not accurately explained or understood.  Sometimes it is even suggested to be a normal or “good” thing that bees enter a state of torpor in cold weather.  These misunderstandings have caused colonies to be lost unnecessarily.

  • We can use efficient hives that are insulated naturally, or if necessary, adding extra insulation.
  • Ensure that hives are well ventilated.  Keeping hives dry can’t be overstated.
  • Use effective pest presence restrictors.  Entrance guards or different sized bottom boards perhaps.  When we try to do whatever keeps predators and scavengers from getting into hives. Colonies can be depleted or have their resources consumed before they can access them.


What Are Bees Doing? Winter Warming

The honey bee colony forms a cluster or “ball” of bees crowding in together once temperatures get to about 59° F or lower.  The warmer it is, the bees hang out in a looser, less tightly crowded condition.  The colder it gets however, the more tightly they pack in next to each other.

Each bee is a walking thermometer and there are “outer bees” in the cluster and there are “inner bees” in the cluster.  The bees take turns being inner and outer bees over time.  All of the bees in the cluster generate heat by using “micro-vibration” in the thorax of the flight muscles.  To watch them, you can’t even tell that they are making any movements of that sort.

“Inner” bees are packed together less tightly than bees on the outside of the cluster.  That’s beecause their jobs, even while clustered, generate heat as well as care for the queen and any brood depending on the time of year.  When there is brood to care for honey bee clusters can and will maintain temperatures of up to 95° F and maintain it as long as there is enough food to keep burning the energy.

winter cluster “zones”

“Outer bees”, those that make up the variably one to thee inches of the cluster “shell” as it were, cluster much more tightly together in order to “insulate” the inside of the cluster through increasing bee density and minimizing the amount of surface area that gets cold.  When there is no brood to care for, bee clusters will “chill out” just a bit working enough to hold temps at about 55-ish ° F.  Enough to keep bees alive and able to move their muscles.

Bees typically “hold it” and wait to empty the waste in their bodies for times when the weather allows them to fly out and away from the hive to do so.  Unless they are ill or otherwise affected, bees won’t make a mess inside the hive.  At least, that kind of mess.

When the temperatures are warmer, the cluster loosens up and sometimes breaks into smaller clusters allowing bees to travel across the combs and even to move the whole cluster ball upwards towards the area where honey or food is still stored.  As the temperatures drop, the cluster re-forms and tightens up again.  Those bees that don’t make it back to the cluster often die.  Clusters that break up into smaller clusters spread apart in the hive that get caught unable to reform the larger cluster are also at risk of killing off the whole colony because there just aren’t enough bodies to keep each “mini-cluster” warm enough.

Bees that get too cold experience something called “torpor” which leads to dead bees.  It’s not the typical behavior of bees to put themselves in such a situation to experience torpor, but it can and does happen far more than any beekeeper would like to see.  Otherwise, honey bees cluster up and stay active and awake inside the hive all Winter long.

And that is what they are doing in there.

Diapause, Do Honey Bees Do It?

One of the most common questions beekeepers are asked is what happens to the bees when it gets cold outside.  Usually sung to the tune of, “Do bees hibernate?”

When it comes to insects, like honey bees, IF they did any such thing, it would probably be “diapause” and not “hibernation”.  To be real loose and cavalier with explanations, “Hibernation” is like taking a very long nap and all the vitals become depressed and slow down.  Think of it kind of like being in a coma.

“Diapause” is more of a state in which development in something like an insect, say… a honey bee, seems to nearly stop cold while bad and ugly things in the environment around them happen.  Again, playing loosely with descriptions, think of it sort of like going into suspended animation when the weather gets too rough to find food or water, etc…

I have had more than one person ask if “diapause” was “The Change” for bees since they were all girls just getting older over the Winter.  No, bees have plenty of other reasons to be cranky, they don’t need another one.  Though in the Winter, they might actually appreciate hot flashes.

As for honey bees though, they do neither in the cold of Winter.    Honey bees are awake and active the whole time.  When temps hit somewhere around 57-ish degrees F or lower, the colony will cluster.

Honey bees survive Winter in their nest by “Clustering”.  That is, they group together in a ball style shape in and around the wax cells in the combs and as a group, shiver their wing muscles to generate heat.  By being clumped so closely together, they keep themselves and each other warm through the Winter.  The colder it gets, the tighter they cluster together.

Winter cluster image courtesy of Randy Oliver at scientificbeekeeping.com

How do they keep up the heat?  By eating honey.  The bees forage for, make and store honey primarily for times like Winter, so that they will have a full pantry and not have to go outside to get more food.  It’s already in the hive.  The more they generate heat, the more honey they have to consume to maintain the energy to do it.  The faster they go through the honey stores, the more likely it is that bees will starve out in the late Winter or early Spring because the food didn’t outlast the weather.

The closeness of their bodies and even the beeswax combs themselves also help to act as some bit of insulation so as to help keep some of the heat they generate hanging around and keeps them, in however little or greater effect, from using too much energy to soon.

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