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How do honey bees keep their hive warm?

Honey bees do not heat their hives the way we heat our homes. Instead, they concentrate on keeping the cluster warm by vibrating their flight muscles. The center of the cluster is the warmest part of the hive, and the temperature drops as you move out from the center.

The interior of the hive is warmer than the outside air because heat escapes from the cluster and the hive itself offers a small amount of insulation. But the bees do not attempt to keep the entire space warm. In fact, the air inside the hive can be quite cold.

Because hot air rises, the warmest place outside of the cluster is right above the cluster. A beekeeper can help keep the hive slightly warmer by placing insulation above the cluster to capture some of this escaping heat.

Bill’s hive temperature experiment

In order to help explain this phenomenon to new beekeepers, Bill Reynolds of Minnesota decided to monitor the temperature inside his hives as the colonies plunged into winter. According to Bill, he purchased an inexpensive desktop weather forecasting station with three remote wireless sensors for his project. He used a fourth sensor to monitor the ambient outside air.

The weather cooperated for his experiment. Bill says, “Here in Minnesota we are experiencing bone-chilling temps around zero each morning and mid-twenties, if we are lucky, by noon.”

Bill set up three hives, each with three deeps topped with a quilt box. One hive contained a colony of Carniolans, one a colony of mutts, and one was empty. In each hive he centered the sensor over the third deep but under the quilt box. He did not attempt to place the sensors at the core of the clusters. During the measurement period, the clusters were two deep hive bodies below the sensors.

The hives were not wrapped. All three setups were on the south side of a house with a straw-bale wall blocking northwest winds. According to Bill, “Other than the sensors, there is nothing different between these hives and any other hive one would find in a backyard.”

Partway through the experiment, Bill began recording separate readings for the outside air and empty hive. He made this change because he noticed that the temperatures increased and decreased at different rates inside the empty hive and outside of it. It became apparent that the wooden boxes themselves influenced temperature fluctuations.

Warmer inside, but only slightly

The graph below shows temperature readings for each sensor. It is quite clear from this simple experiment that temperatures inside the active hives rose and fell with the outside temperature, but overall the inside remained warmer than the outside. But far from being cozy, the inside temperatures dropped down into the 30s on the coldest days. It is interesting to see that the two colonies were very consistent with each other, rising and falling in tandem.

It also became clear that the interior of the empty hive box was somwhat warmer than the outside air. I suspect a combination of sun and minimum air movement through the boxes increased the temperature slightly.

Thank you, Bill, for your experiment and awesome graph. Nicely done!

*Ambient Weather WS-10 Wireless Indoor/Outdoor 8-Channel Thermo-Hygrometer with Three Remote Sensors

Rusty
HoneyBeeSuite

Graph showing the temperatures inside the three hives, and beginning November 15, outside the hives.
Graph showing the temperatures inside the three hives, and beginning November 15, outside the hives. © Bill Reynolds.
The two populated hives in a warmer time. © Bill Reynolds.
The two populated hives in a warmer time. © Bill Reynolds.

*This post contains an affiliate link.

Comments

cgrey8
Reply

I find these studies of internal temps fascinating. I work for an HVAC controls manufacturer. We make the computer controllers that monitor sensors and control motors, actuators, heaters, and anything else that either needs an ON/OFF control or variable output control (i.e. 0-10v output). So it’s not been far from my mind to setup a similar experiment with a number of strategically placed thermistor sensors in a hive to do something similar. Perhaps in a few years I might take the time to do something like this and even put access to the temps and trends in real-time on the Internet for others to view. I think it’d be interesting to know how the temps both in winter and summer vary from ambient outside temps for my hives. For now, I’m satisfied just reading about other people’s experiments like this one. If you know of others, please post them.

Somewhat unrelated, I have been monitoring my cluster by putting the white boards under the hives. Some of that was to help keep the wind out of the hive (I know you say that isn’t necessary). But I also wanted to monitor where the hive cluster was…mostly out of curiosity. And sure enough, you can see exactly where they are by the debris left on the board just after 24hrs. And as usual, you are right, they do still have varroa. I saw 4 dead ones on the board.

And don’t worry, I won’t leave the boards in there just to continue to collect debris. I know that’s a breeding ground for beatle eggs. Although in the temps we are getting right now, would any eggs actually survive?

Rusty
Reply

Chris,

The beetle eggs won’t survive a good freeze, so it depends on where they are. Eggs on the debris board most likely will freeze. Good riddance.

Bill
Reply

Rusty, I should mention that the clusters are two deep hive bodies below the sensors.

Bill

Rusty
Reply

Thanks, Bill. I added that in.

Rich
Reply

“Because heat rises,”….. Well, heat moves from hot areas to cooler ones. Saying “heat rises” is actually true, but only as much as it also moves sideways or downward in a given medium for all three major means of heat flow, and in the absence of a medium (a vacuum), by radiation. It is better to note that “hot air rises.” That is caused by the buoyancy of heated air, which is less dense than cold air.

What an annoying comment by me, eh?

Rusty
Reply

Rich,

1) You are right, of course. I will change the phrase to “hot air rises.”

2) Yes, you are annoying. But after 40 years, I’m used to it, eh?

Nancy
Reply

Bill, thank you for the detailed experiments and data! Readers, an indoor-outdoor temperature monitor is available from Oregon Scientific. I would not know what to do without mine for greenhouse, barn and garden.

About the slightly warmer temperature in the unoccupied hive box: assuming you are using screened bottom boards and no varroa drawer, that warmth could be geothermal. I am reminded every sub-zero day I walk inside the barn (dirt floor and good roof, but no heat source besides 12 goat and 3 horse bodies), that warm air rises from dry ground, which is usually at about 40 degrees.

Yesterday, anticipating last night’s 13F, I placed the insulation-board shelters around all four hives. I did not add the varroa boards, for the sake of ventilation. Now that Bill’s work has called to mind ground heat, probably just as well. We’ll see.

Thanks Rusty and Bill!

Nancy
Shady Grove Farm
Corinth, Kentucky

Rusty
Reply

Nancy,

You are absolutely right. I have a garden shed with a concrete floor. It stays about 40 degrees all winter long regardless of the outside temperature. It always amazes me.

Bill
Reply

My chicken coop has a concrete floor, straw and some forty critters, and it don’t stay that warm Rusty…

Bill

Rusty
Reply

Well, Bill, this ain’t Minnesota.

Mark Martin
Reply

Very cool experiment! I actually built an electronic sensor board that doubled as a ventilation board for my hive this year. I had one sensor on the outside of the hive, one sensor that I dangled down into the brood area and one sensor inside the vent board on top of the hive. It was very interesting to see the data and how they regulate the temperature in the brood nest to around 95 no matter what. You can see it clear as day in the graphed data here:

http://beeginnings.blogspot.com/2014/06/second-inspection-2014-06-10.html

Aaron
Reply

Along these lines, I noticed some of my bees are flying today as the outdoor temp approaches 40 F. for the first time in what seems like a few weeks. We had a lot of rain right before Thanksgiving, then 4″ of snow, followed by a 4 day-long cold snap that’s just starting to ease. Glad to see them out doing the needful, though I thought they wouldn’t/couldn’t fly in temps much below 50. I sure am glad I got the moisture quilts/boxes on before the weather really set in. Didn’t get the slatted racks in place in time, so I imagine it’s going to wait until spring now.

Rusty
Reply

Aaron,

I’ve seen them fly in cold weather as well, but I think they just make quick cleansing flights and return. They don’t go foraging for anything.

Chantal Chopin
Reply

Dear Rusty,

I have a question I hope you might be able to answer: I have a varroa floor and a board with sticky paper underneath. Yesterday, I changed the sticky paper and noticed dead bees on it. I had a look underneath the mesh floor and I noticed a cluster of bees there. I had closed the gap at the back of the hive to try to keep the bees as warm as possible with just enough space for air to come through for ventilation. Still about 30 bees had managed to creep in and clustered there. Although we are in Winter, the temperatures over the last few days have been quite mild, about 10 degrees celsius. Would you know why this happened? Have you encountered it before?

I left the bees where they were because it was the end of the day. Today, I removed them because they were all dead unfortunately and I completely blocked the gap, just allowing a bit of air to go in and out but no bees.

Thanks for your reply.

Rusty
Reply

Chantal,

I can only guess. Since 10 degrees is warm enough for some of the bees to fly, they may have left for a cleansing flight and not been able to find their way back into the hive. They followed the scent (perhaps) that led them to the area underneath the varroa floor.

I haven’t seen this exact scenario, but I have seen confused bees gather on the outside of a hive or underneath it. If your bees were hatched since the colony has been clustering for winter, they may be inexperienced with finding their way back home.

May sure you leave an entrance for them to come and go. They will need it on those warmish days.

Eddy Radar
Reply

I am unclear on ventilation for the hives. How can I tell if there is enough? How do I increase/decrease it? What are the patterns of air flow in Langstroth and in top bar hives?
Because it is so damp here, I was thinking to put a seeding mat under the back half of my top bars (I have those narrow 6″ wide ones!), hoping it would keep it a bit warmer and therefore drier. Will the screened holes at the top of the body provide enough air circulation, and will the bees really remove the propolis which now seals these holes if they need more?

Rusty
Reply

Eddy,

For more about ventilation and air flow in hives, go the the main menu (top the the page) and click on “Physics” tab.

Be careful of using artificial heat in your hives. The bees may be fooled into thinking the outside temperature is warmer than it actually is. They may flight out into the cold and be unable to get back.

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