Wyoming winter beeyard on a good day.

A plex cover was built to observe have condensation. Here’s what I saw:

  • in a dry climate, a division board filled with water is beneficial
  • for a healthy hive, condensation is always a valuable resource
  • very little winter condensation
  • no winter condensation occurred above the cluster
  • late winter early spring condensation stimulates colony expansion
  • greatest condensation occurs during early spring brood rearing when winter clusters break up
  • very little summer condensation which is quickly consumed
  • fall condensation mirrors late winter condensation
  • condensation never melted or dripped on the cluster
  • natural comb bees consumed less water
  • these observations are similar to those in England, a wet and different climate

Give the plex inner cover a try and monitor condensation. The results could change your management strategies for the better.

If so, let others know.

Upper entrances, for hive ventilation, are recommended by all the popular bee books. Yet, swarms often 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 propolis is harvested using this behavior.

Providing upper ventilation is a curious management strategy. The bees sure don’t want it.

The Test

Plex Cover

To observe condensation without disturbing the bees, a plexiglass inner cover was built. Then, a beehive with the plex inner cover and a migratory lid were placed next to my house.

Natural Water Sources

Wyoming is a dry and thirsty land.

  • winters are long, windy and cold
  • spring weather is unsettled
  • summers are hot and short
  • natural water sources are, at best, sporadic

Melting snow banks offer spring water. It’s cold and many bees are lost when the weather rapidly deteriorates.

After the snow banks are gone, irrigation is the only consistent water source. Irrigation ditches are filled by early summer. Once the irrigation ditches are turned off in late fall water sources are mostly lacking.

In Hive Water Supply

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:

  • a division board feeder was put inside
  • a wooden float in it
  • it was filled with water
  • and 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
  • 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
  • these bees completely ignore their outside water source
  • continued to take water from the feeder when they don’t have outside access during bad weather and at night

During a moderate honey flow, the division board water is ignored:

  • it would quickly become septic
  • required dumping the feeders on occasion, a nasty task

Internal Feeder Removed

Once I removed the feeder:

  • at 5 minutes, bees were running on the frames looking for the water source
  • at 15 minutes the hive panicked
  • most hive activities stopped
  • bees ran throughout the hive and around the entrance
  • they quickly found the neglected outside water source
  • at 30 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 3 hours after the feeder put back inside the hive.

After that, activity at the outside source returned to a more normal level, with a half dozen bees taking water. After that, the bees never gave up working their outside water source.


These observations were so unusual, that the plex hive with it’s internal water source was monitored for 4 years. This hive consisted of 3 deep supers with 3/4″ holes drilled in the upper corner of each super.

Late Winter – Early Spring

Once internal hive temps got warm enough to keep the feeder 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 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 within several hours

Top ventilation greatly reduced this condensation. It’s an expensive loss of clean, warm water that must be replaced by cold, hard to forage water, outside the hive.


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.


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 1/3rd 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

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. It’s no surprise there’s so little winter condensation.

  • honey consumption is minimal
  • brood rearing is almost nonexistent
  • and cluster temperatures are at their lowest

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

By late December, water levels and condensation remained unchanged for weeks.

But when the weather warmed enough to melt ice in the feeder, the bees would rapidly consume available water and drastically drop the feeder’s water level.

Sometimes the level would drop 4 inches in 24 hours. Initially, a leaky feeder was suspected. But that wasn’t the case. When the bees needed a drink, they came to the feeder and got one.

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.

Discolored Top Bar Ends

I’ve used this discoloration as an indication of excessive winter moisture. It’s a poor indicator. A thirsty hive gets discolored top bar ends even without much condensation.

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 hive’s exterior 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 even when no moisture was directly above the cluster.

Natural Comb Sized Bees Are Different

My natural comb bees consume water like my large cell bees do in the spring through fall. But winter consumption is different. They work 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
  • maybe the closer comb spacing is less drafty


Water – Ventilation Management

I changed my water management practices for my conventional foundation based hives:

  • provided internal water from December through May
  • all upper ventilation is eliminated during winter without adverse effects
  • normal sized, healthy cluster didn’t suffer from 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 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. But the excessive moisture is symptomatic of other problems.

I’ve over wintered hives outdoors in interior Alaska where temperatures didn’t climb above 0 F for months. And extreme temperatures approached -70 F 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 when they were healthy and had enough food.


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 providereadingy 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 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.

Climate and Situation are Everything – Maybe

My hives are located in a dry, 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.


Dave Cushman, a English beekeeper, 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

Be sure to check out Dave’s Site .

Your Location

Unfortunately, to find out what your bees need requires monitoring them for yourself.

  • a plex cover is an excellent way to do that
  • a lexan cover could be considerably cheaper than plexiglass but wouldn’t be as durable
  • even a plastic sheet cut to size could provide a seasonal view

Watch your bees and 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 might be a bigger problem than winter condensation.


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