Winter condensation is a valuable water resource.

The Thought

Wyoming winter day.

Wyoming winter day.

Upper entrances, for hive ventilation, are recommended by all the popular bee books. Yet, when swarms are given the choice, they reject a cavity with upper ventilation. When hives are given upper ventilation, the bees will reduce or eliminate it if possible. This behavior is so strong that premium grade propolis is harvested using it. Providing upper ventilation is a curious management strategy. The bees sure don’t want it.

The Test

Plex Cover

I built an inner cover using plexiglass set in a wooden rim. I could look through this plex cover and see the bees without disturbance. Winter bee behavior and winter condensation were easily monitored. Then, I placed a beehive, with the plex cover, and a migratory cover on top the plex cover next to my house.

Natural Water Sources

I live in a dry, thirsty land. Winters are long, windy and cold. Spring weather is unsettled. Summers are hot and short. Natural water sources are, at best, sporadic.

Beekeeping is possible only along natural drainages and in irrigated agricultural areas. Melting snow banks offer spring water. It’s cold and many bees are lost when the weather rapidly deteriorates.

The irrigation ditches are filled by early summer providing water for the bees. Water sources are almost completely lacking once the irrigation ditches are turned off.

In Hive Water Supply

10 Degrees F. Moisture is frozen.

10 Degrees F. Moisture is frozen. The division board feeder with wooden float is at the bottom of all these photos.

Anytime hive temps climb and melt the frozen condensation on the plex, the bees lick up the water. It’s gone in several hours. The bees drink even when their water source was frozen outside. So this wild and crazy bee wrangler took a division board feeder. Put a wooden float in it. And filled it with water. The feeder was placed on the warm side of the hive. It’s at the bottom of all of hive photos.

Colony death by drowning, right? Not so. This hive quickly learned water was available. And they freely used it. Water levels would drop about 1″ per day. By spring’s end, this hive was as strong as any of my hives. It started brood rearing earlier. And bee population remained more stable throughout bad spring weather.

Bees completely ignore their outside water source when water was provided inside the hive. Bees continued to take water from the internal feeder when they normally don’t have outside access such as during bad weather and at night.

Internal Feeder Removed

The division board water is ignored during a moderate honey flow. And it would quickly become septic, especially with a few dead bees floating in it. This required dumping the feeders on occasion, a nasty task.

At one point I removed the feeder. Within five minutes, bees were running on the frames looking for the water source. Within fifteen minutes the hive panicked. Most hive activities stopped. Bees ran throughout the hive and around the entrance.

They quickly found the neglected water source outside the hive. Within thirty minutes, hundreds of bees were hauling water into the hive. The activity was frenzied, much like a miniature version of honey robbing.

This frenzied activity continued for three hours after I replaced the feeder inside the hive. After that, activity at the outside source returned to a more normal level, with a half dozen bees taking water. But the bees never gave up working the outside source after that.


These observations were so different from what I¬† expected, that I maintained the plex hive, the internal water source and monitored them for four years. This hive consisted of three deep supers with 3/4″ holes drilled in the upper corner of each super. Here’s what I saw:

Late Winter – Early Spring

Once internal hive temps got warm enough to keep water from freezing, the bees regularly consumed it. When outside temperatures were around 30 degrees, the bees, although clustered, would send an expedition to haul water back from the feeder. And they would consume condensation on the plex. The water stimulated them just like feeding thin sugar syrup does.

The greatest condensation occurs during the spring, when brood rearing is underway. Then, bees consume lots of honey while clustered. The cluster is an effective means of controlling both heat and humidity.

When the cluster breaks, abundant moisture is released. Large water drops condense across the plex’s full extent. This extra moisture is quickly consumed in several hours. Top ventilation greatly reduced this condensation.

20 Degrees F. Moisture is frozen.

20 Degrees F. Moisture is frozen.

30 Degrees F. Moisture is liquid. Notice the few wandering bees.

30 Degrees F. Moisture is liquid. Notice the few wandering bees.


Only a small amount of condensation was seen during the summer. Small droplets would condense around the outer edges of the plex cover before sunrise. The bees would quickly consume this resource. Some additional condensation occurred directly above the feeder.

40 Degrees F. A few bees are working water in the feeder.

40 Degrees F. A few bees are working water in the feeder.


Water uptake paralleled the amount of brood reared. As brood rearing reached a minimum in October, little water was consumed. Fall condensation mirrored spring condensation, but the overall amounts were slightly less. Open vent holes almost completely eliminated what little moisture condensation occurred in the fall.


For winter, the 3/8″ hive entrance was reduced to one third its length. A wind baffle was inserted to prevent Wyoming’s howling winds from blowing directly into the hive. The hive was wrapped in a single brown plastic tarp which provided more protection from the wind. All vents holes were plugged.

By late December, water levels would remain unchanged weeks. But when the weather warmed enough to melt ice in the feeder, the bees would rapidly consume available wate and drastically drop the water level in the feeder. Sometimes the level would drop four inches in a twenty-four-hour period. Initially, I thought I had a leaky feeder. But that wasn’t the case. When the hive needed a drink, they came to the feeder and got one when it wasn’t frozen.

Water, in the feeder, remained liquid when outside temperatures fluctuated at 20 degrees. When outside temps consistently dropped below 20 degrees, the water would freeze. Then the bees stopped working the feeder and plex cover for moisture.

Winter condensation was never a winter threat. It was a resource! It never dripped on the cluster. The area directly above the cluster remained free of condensation.

The bees are tightly clustered during the winter and tightly control water loss. Honey consumption is minimal. Brood rearing is almost nonexistent. And cluster temperatures are at their lowest. It’s no surprise there’s so little winter condensation.

Opening or closing the vent holes had no effect on the plex’s winter condensation. The feeder’s presence made no difference in the amount of winter condensation on the plex cover.

During the winter, outside temperature was the determining factor for condensation on the plex cover as it controlled how tight the bees cluster.

Minus 20 Degrees F. The water division board feeder is at the bottom of these photos. This moisture is frozen.

Minus 20 Degrees F. The division board feeder with water and wooden float is at the bottom of these photos. This moisture is frozen.

Discolored Top Bar Ends

Maximum moisture occurs when the cluster is actively rearing brood and disperses during the day, in the early spring.

Air rises above the cluster to the hive’s top. It cools. Then flows down along the exterior portions of the hive. Eventually, condensation occurs. If the temperature is low enough, the moisture forms ice. In my climate, ice formed only against the exterior hive’s portions and never directly above the cluster.

In the spring, black mildew was found on the top bar ends. This indicated that moisture sat in the frame rest area. That’s the coldest part of the hive with only 3/8″ thick wood or less. It’s possible that only a thin layer of propolis separates the hive interior from the outside when the supers were worn.

I had always used this discoloration as an indication of excessive winter moisture. It’s a poor indicator. A thirsty hive gets discolored top bar ends.

Natural Comb Sized Bees Are Different

My natural comb bees consume water like my large cell bees do in the spring through fall. But their consumption is different during the winter. They consume the condensation but pay little attention to the feeders. They haven’t taken that big drink like my large cell bees. It seems they get all the moisture they need from the condensation.

Maybe natural comb bees need less water during the winter. And that could one reason why they over wintered so well for me.


Water – Ventilation Management

Maximum condensation when it's cold, the bees are rearing brood and the cluster breaks.

Maximum condensation when it's cold, the bees are rearing brood and the cluster breaks.

I changed my water management practices and provided internal water from December through May. All upper ventilation was eliminated during winter without adverse effects. Any normal sized, healthy cluster didn’t develop problems with winter moisture.

Very small clusters, in a cold place, can get wet. I over wintered five frame nucs in a stack. One nuc, with a very small cluster, got too wet. It was located on the north side at the bottom of the pile and mold grew on the cover. The nuc survived but was clearly damaged by excessive moisture.

Hives that dwindle due to disease, parasites or poor nutrition can suffer from excessive moisture during early spring. But the excessive moisture is symptomatic of other problems and not the cause.

I’ve over wintered hives outdoors in interior Alaska where temperatures didn’t climb above zero degrees F for months. And extreme temperatures approached 70 degrees F below zero for weeks. Clear rim ice would form inches away from the cluster. Hoar frost would fill up the rest of the box. Yet, these hives didn’t succumb to excessive moisture if they were healthy and had enough food.


Bees working the water shown above.

Bees working the water shown above.

Bees, in a natural cavity, wouldn’t have much top ventilation. If the bees were in a tree, Most insulation is above and below the cluster. If the entrance were at the cavity’s bottom, airflow would rise above the cluster and descend along the nest’s outer margins. Most condensation would occur in those outer margins. It wouldn’t drip on the cluster but would provide a ready source of scarce, winter water.

Water might be absorbed by the wood in the nest cavity. It could act like a sponge and work like the feeder in my hive.

A water source inside the hive would moderate the need to forage under marginal conditions. Broodnest humidity could be more easily maintained. And granulated honey could be used before outside water sources are available.

As outside conditions improve, the natural moisture flow is down the sides and out. That would follow the natural airflow direction enhancing cavity drying.

A lack of moisture often becomes a problem with bees wintering indoors. When inlet air temperatures are low and airflow rates are reduced, they become very dry. Rather than generating excessive moisture, the bees run short during the winter. When this happens, the bees die. Piles of crispy, shrunken bees are found outside the hives. If the bee’s stores are granulated, a massive bee loses occurs.

The bees don’t generate a water surplus during winter in my climate. Some water source is a necessity during the winter

Climate and Situation are Everything – Maybe

Two hours later, no condensation. It's a resource, not a problem!

Two hours later, no condensation. It's a resource, not a problem!

My hives are located in a dry, very windy climate. Their entrances aren’t blocked by snow for more than a few weeks at a time. Our skies are mostly clear and sunny during the winter. The bees break cluster about once every three weeks or so. They need a canteen during the winter here.

In a climate, where hives are covered with ice and the skies are cloudy all day, the water situation could be different. Yet, as far as I know, the bees still seal the upper hive areas in these climates. Maybe bees, in a situation like this, need an umbrella and not a canteen.

Unfortunately, to find out what your bees need requires monitoring them for yourself. A plex cover is an excellent way to do that. A cover made from lexan could be considerably cheaper than plexiglass but wouldn’t be as durable.

If you watch your bees, let others know what you see. Post your results on one of the bee lists. With enough observations, hive water and ventilation will become better understood. I suspect that a winter water deficit occurs in most situations.


Dave Cushman, a beekeeper in England, sent me an email. He wrote:

“I used glass tops and a few plastic ones, what was seen was a dry circle in the middle and spherical drops right out to the corners.

The size of the central circle varied, the centre of the circle moved about a bit (our colonies do not fill even our smaller boxes). The size of the droplets got smaller towards the actual corners…..”

Best Regards & 73s, Dave Cushman… G8MZY

Dave’s Site

Working with bees on winter hive ventilation/water has made my beekeeping easier. I don’t provide top ventilation during the winter. And I reduce my entrances to 3/8″ by 5″.

With this arrangement, bees get the ventilation they want, and the winter water they need without any extra feeding or effort. They don’t suffer from damp conditions.

Will it work in your climate? Build a plex cover and see.

18 comments on “Condensation

  1. Please dig through the little book:
    “Constructive Beekeeping”
    by Ed.H. Clark (written in 1918)

    Download and/or read online

    He has many good thoughts in condensation vs. ventilation in bee hives.

    Not just in winter – even in summer condesation could be a great benefit to the hive, especially when drying nectar into honey, using the condensation to produce brood food. (Beebread + water!).

    It isn’t efficient to ventilate all the evaporated water of the nectar – and thus having to bring in water afterwards. It is efficient to condensate the water inside the hive and use it straight from there for brood food production.

    Modern hives tend to over-ventilate, open mesh floors and such.

    Read yourself. It is well worth mining in that book.


  2. I have a indoor new oberservation hive, 5 meduim frames
    single thickest. I have condensation on the inside of glass
    new Queen in about 4 days from emerging. lots of new bees have hatched so my hive is almost full. The hive has
    plenty of air vents, I have put a small fan on the hive and that helped with the condensation and the bees that are at top new frames (moving around not really on the frames) moved down to the lower 3 frames that were from another hive, When they moved down the condensation moved with them, I lowered to fan and that helped again. Is this something I should worry about

    • Hi Sandi

      Does the water collect and drip out the bottom of the hive? Or is it more like breath on a mirror. At any rate, I’d let the bees control the environment and ditch the fan, unless lots of water runs out the bottom of the hive.

      A broodnest is a very warm and humid place(95F and +90%). With a single frame wide ob hive, there can be quite a temperature differential between the comb and the glass 3/8 inches away.

      Regards – Dennis

    • Hi
      Although you say the condensation is a valuable water source. When there is a thaw, in February for a few days and then back to -30c…. doesn’t the condensation rain down on the bees making them wet before they can drink it and then they die when it gets cold again because they are wet and they freeze????

      • Hi Bev

        Not in my experience with a normal size, healthy colony in a non-arctic climate . Very little if any moisture condenses directly above the cluster. Most of it condenses along the outside edges.

        Make a plex cover and check it out. I think a piece of translucent plastic could work as well as the cover.

        Regards – Dennis

  3. Dennis,

    I have followed your test and have plexiglass inner covers on 6 hives in 3 different locations. My cheap and basic blog shows the pictures from beginning to present. I live in central virginia and we are currently having fluctuating temps from 50′s in the day to 30′s on other days…

    • Hi Doug

      Thanks for sharing the pics. I’ve had my condensation page up for over eight years and only had a couple of people put it to the test and respond.

      Let me know what you see through the seasons.

      Regards – Dennis

  4. Dennis,

    Many beekeepers are using screen bottom boards. Many are leaving these open all year. Do you have an opinion of how this practice affects hive moisture dynamics?


    • Hi Larry

      Back in my mite counting days, I ran screened bottoms on all the Langs in my test yard. But I didn’t run them open the entire year. I put a migratory bottom below them and reduced the entrance for winter.

      I live in an exceedingly windy place. It’s not uncommon to have sustained 60mph winds with higher gusts during the winter. A hive with a screened bottom left open soon perishes under these conditions.

      I no longer count mites or use screened bottom boards. So, my experience is rather limited.

      Regards – Dennis

  5. Hello,Ilive in northeastern pennsylvania. there are Several folks that are starting top bar hives. I am doing reasearch on the process of over wintering honey bees.Our state university as well as the traditional beekeepers in our area are not sure if these hives will survive the winters here. I am hopefull that they will, and also stronger bees due to the concept of the bees replacing wax that is harvested may help fight Comb collapse syndrome. I feel properly maintained top bar hives in homeowners gardens will be a large step in helping the honey bee in our Pennsylvania. What do you think about this project? Thanks Scott.

    • Hi Scott

      Great idea! Sam Comfort has lots of east coast top bar hive experience. He’s a great resource. Don’t be put off by Sam’s anarchy. He’s one of the most friendly, helpful, chilled out guys you’ll ever met.

      Let me know how things work out for you.

      Regards – Dennis

      Regards – Dennis

  6. Dennis,

    Help me understand this a little better. Condensation is created when warm moist air is in contact with a cold surface, so I understand why you are having it. In a hollow tree there are no cold surfaces due to the insulative properties of the wood. Does the wood soak up the moisture? and can the bees draw their moisture needs from the wood?

    Thanks, James

    • Hi James,

      Beg to differ with you. When the bees are tightly clustered and have been that way for awhile, there’s very little difference between temperatures outside the cluster and ambient temperatures outside the hive. Although the walls of a feral nest are thicker than those of a man made hive, the wood is still colder than the cluster. Any moister/heat that escapes the cluster will condense on the cooler wood.

      I too have wondered about the possibility of the wood acting as a sponge. But I don’t have any actual experience to state that it would be so. There are almost no wooden cavities suitable for bees here. And feral hives seldom survive here.

      Have you been able to watch a feral hive?

      Regards – Dennis

      • The nesting area inside the tree is coated with propolis. Propolis (resin) creates a seal covering the interior surface and would not allow moisture to be absorbed.

  7. Hello, I’m not sure I’m following you 100%. Could you please clarify – I’m a novice. You say you are using a simple plex glass cover on your hives, but you also mention a water feeder? I get the plex cover, but I was looking for pics of the water feeder and was not sure if you meant a hive top feeder with just water you add yourslef, or if you had a system of letting the moisture from the plex glass drip into a pan or feeder of some sort.

    Either way, based on what I’ve been reading on natural beekeeping it does indeed appear that the bees will seal off roof ventilation. Maybe the reason is that they want condensation to form in the hive so they don’t have to go out in winter time to get a drink.

    Sounds like you may be on to an important observation or discovery on natural bee keeping. Would you recommend that I use a simple plex glass cover? I’m using Langstroth hives and I live in N Georgia – winters are not too bad compared to where you are.


    • Hi Geno,

      I don’t use a plex glass cover on all my hives. It was just an observation device I used for a few years on a single hive. And I seldom use it anymore.

      I fed water to the bees using a plastic division board feeder placed in the top box, on the warm side of the hive. It has a wooden float in it and is consistently at the bottom of the pictures on the condensation page. Thanks for the heads up. I’ll go back and add some details to make the page easier to understand.

      I’m not sure about a hive’s winter water needs in Georgia. It would be a easy task to make a plex cover and put it on a single hive. Follow the bees through several years. And share the results. I’d be very interested to know what you find out. A plastic sheet could be used in place of the plex cover. Photos through it might not be so clear. But it would be cheaper and would work fine for observations.

      In areas, like mine, where winters are hard and long, winter condensation and the bees water needs are minimal. The bees are continually clustered. And the cluster is very effective at conserving both heat and water.

      But it’s during the early spring, when the bees frequently break cluster for part of the day and then reform the cluster at night lots of heat and water are lost. Much of that water condensed above the bees and is definitely a resource. In In Wyoming this happens in late March. In Georgia, it might be a mid-winter behavior. At any rate it’s a dangerous time for a bee outside the hive.

      Regards – Dennis Murrell – BWrangler

  8. Hi Dennis,
    Haven’t been to your site for some time–nice upgrade!

    Great page on condensation–answered some burning questions.

    My old email for you doesn’t work. What’s your new address?


    • Hi Randy

      Looks like you’ve been very busy since we last corresponded. I’ve followed your articles in the Bee Mags and your posts on Bee-L from time to time. And consider them very balanced and a must read.

      Hope all is well with you. I know you’ll be getting some more sleep once you’re out of the almonds. ;-)

      Regards – Dennis Murrell – BWrangler

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