What a mouse in a hive looks like

Once a mouse enters a hive they typically chew out the bottom corner of a few frames to make space. They will then bring in nest material. This is a view from the bottom of the box:

Mouse nest viewed from bottom of hive box.

You will probably see evidence of the nest on the bottom board as well.

If you are using a screened bottom board, there is a good chance you can determine if you have a mouse just by looking at the tray under the screen for mouse droppings and fallen nest material.

Signs of the mouse nest under the screened bottom board

It's said that mice will often move out as it starts to warm up and the bees become more active. If not, the bees can attack the mouse and you may find the remains (possibly propolized) within the hive.

Aside from the damage to comb, mice are also problematic in the pungent stench of urine that they leave behind in the hive.

Evidence a shrew has been around the hive

Pygmy ShrewPhoto by: minipixel / CC: Attribution-NonCommercial-NoDerivs License

Shrew's don't nest in the hive, but they do leave behind signs of their visit. You may find droppings that are slightly different than those of mice. There will also be bee carcasses. Shrews eat the bee innards and leave behind a hollow exoskeleton. Most often they get at the innards via removing the head of the bee.

Shrew eaten bee carcass

If you do successfully exclude shrews from your hive, you may still find these decapitated dead bees outside the hive. It seems like they will feed on either the dead bees taken out by the undertaker bees, or those bees that leave the hive to die. Shrews are small but they need to eat frequently, over the course of a winter they can take a significant toll on the bee population.

Shrew and Mouse excluders

Generally the standard wooden entrance reducer is not sufficient for excluding mice, there are many stories of the wood being chewed away to enlarge the opening.

For a few years I've seen good results from both simply adding nails to standard entrance reducers and cutting myself thicker wooden entrance reducers from 1.5" wide wood. Was I just lucky?

Entrance reducer made from a wide piece of wood.

It's very popular to make or purchase metal excluders with holes drilled into them.

Installing mouse exclosuresPhoto by: Tie Guy II / CC: Attribution-NonCommercial-ShareAlike License

The use of hardware cloth as a mouse excluder is not uncommon either.

Hardware cloth to keep mice out of a beehive

Size of entrance required to exclude mice and shrews

The openings beekeepers use for a mouse excluder are sized between 1/4" (6.35mm) and 1/2" (12.7mm), with commercial products typically using a 3/8" (9.25mm) diameter circle. 

There's a fine line between leaving enough space for adequate ventillation, allowing bees to remove the dead, and to bring pollen in during the early spring, while still securely preventing mice from entering. There's lots of debate as to whether a 1/2" gap is sufficient to keep the mice out versus 1/4" making it too difficult for the bees to do everything they want to do.

As far as the 1/2" camp goes, there are some beekeepers who claim to have not had a problem in 40 years. There's also some references from mouse owners using 1/2" mesh cages for adults (but many in the mouse world do seem to cite needing 1/4"). Are their regional differences, like species of mice, as well as how likely it is to find smaller, younger mice at the time of winterizing, your hive?

I haven't found as much info out there about shrews. There is reference online to Fletcher Colpitts, Chief Apiary Inspector of New Brunswick citing the use of both 1/4 and 3/8" spacing for winter and then switching to 1/2" once there is spring pollen. Anecdotally, I can say I am finding beheaded hollowed out bees this year outside, but not inside of the hive in the photo above which is using 1/2" mesh with the vertical opening height made slightly smaller as it overlaps the wood of the hive. I take that to be a positive sign.


Dennis Murrell on Condensation

Dennis had a post on his site with a very interesting look at the importance of condensation in the hive. His site no longer seems to be up, but an archived copy of his site is still available.

With American beekeepers in particular, the idea of upper entrances for ventilation is very popular. What Dennis observed while using a water feeder inside a hive by placing a plexiglas cover on top of his hive, seems to go against that practice.

He observed that very little condensation occured during the winter.  A good deal of condensation did occur during the spring and fall, but the bees quickly made use of this. His feeling was that this saved them the work of collecting water from outside the hive, and provided a needed water source for his bees when an external source was not necessarily available.

Will his ideas work for you in your climate? I don't know, but I do feel the topic of ventialtion and upper entrances probably deserves a little more thought and consideration than most bee books suggest.

September 24 - October 16

We fed the bees around 11 times. 1 - 1.5 kg of sugar in a 2:1 syrup solution each time. On October 15 we saw little evidence of capped honey in the upped warré box, and the outer combs appeared as thought they could be empty. The middle frames of the nuc contained reasonably large patches o capped brood. On one of those frames we also found a queen cup containing many eggs and on the following frame we saw the queen. On the 16th, With the cooling tempratures, the bees had not taken down any of the feed we had left them on the 15th. At this point we turned the top feeder into a quilt filled with saw dust.

November 13

As there was high amounts of DWV in this yard over the fall, we decided to use an organic mite treatment. As we quickly applied the oxalic acid dribble, we saw a modest, but encouraging number of bees for a colony which has struggled to get going all season. In the warré box we obsevered bees on all but the outer-most combs and in lang nuc adapter box there were two combs of bees. On the other hand, this leaves us concerned that they might not have enough stores for winter despite our efforts to feed them. We added 1.5" spacer box under the quilt and used this space to provide about 2.5 kg of dry sugar on top of newspaper as an emergency food supply.

November 15

As it was getting dark and we were cold the previous day, we came back to give the hive tar paper wrap for winter. The high for the day was around 11 degrees celcius and the bees were flying, and to our surprise even bringing back some pollen:

Mid-November and they are still foragingPhoto by: Shawn Caza / CC: Attribution-NonCommercial-ShareAlike License



Mike Palmer - The Sustainable Apiary talk

In this video Michael Palmer speaks to the Prince Williams Regional Beekeepers' Association about his practice of overwintering nucs to make up for loses as opposed to buying new colonies.

In part one he covers the benefits of of overwintering nucs, choosing which colonies to use to make your nucs, how to create the nucs.

In part two he looks at some of the unique management practices to this system and some of the equipment options.

November 4

Due to high mite levels we gave the bees a oxalic acid dribble.

The temprature was around 4 degrees celcius and no bees were flying. We finally saw some honey in the bottom box. The hive wasn't as heavy as it was but still had some weight. Most of the bees seemed to be clustered towards the eastern side of the box, thus the cluster is a little more tall and narrow rather than the ideal fat and round. We did see some small amount of mold on the edges of the top bar cloth above the cluster. This suggested to me that their was a lot of moisture from the feed to evaporate and the insulation from the quilt may not be sufficiently effective at the very edge.

hive wrapped for winterPhoto by: Shawn Caza / CC: Attribution-NonCommercial-ShareAlike License

We wrapped with tar paper and wished them luck.


In the spring we often find that our hives have had to cope with excess moisture building up over the winter months. When it's bad, winter moisture problems will lead to mouldy comb and cold water dripping onto and chilling the bees.

mouldy beeswax comb

The typical cause?

The bees themselves will produce a great quantity of moisture just by living and breathing as water is a byproduct of consuming honey. Warm moist air rises, spreads along the top of the hive, comes into contact with the colder side walls and inner cover, condensation forms and drips back down into the hive.

mould in the hive

The simple and oft suggested remedy to this problem is to provide some form of upper ventilation. Some swear by the top entrance, but that option seems a little drastic to me as the bees are likely to lose much of their upward moving heat at the same time as the moisture (thus requiring more honey consumption, which will in turn lead to more moisture production).

How can we avoid moisture problems while minimizing heat loss?

I used to believe that the short answer to this problem is to insulate and absorb. That we needed to give the moisture somewhere to go and try to minimize the temperature difference between the surfaces of the hive and the cluster. Particularly the top surface of the hive, as moisture is most problematic if it condenses above the cluster and might drip back down onto the bees.

It's been suggested this problem might be less likely to occur in a wild hive, where the tree wall is thicker, and there is much more than a thin layer of wood above the hive. beehive humidity box

So how can we attempt to emulate those conditions with modern day man-made hives?

At first, aside from insulating the sides of our hives, we added 'ventilation boxes' or 'quilts' on top of our hives. Essentially a short box filled with straw, wood shavings or other absorbent material. The side has screened holes, which keep the mice out, and allow moisture to escape. Burlap is stapled to the bottom.

Adding a vent box to beehive

In the photos you can see we placed it above an inner cover with a vent hole, but it could be placed directly above a brood box.

beehive ready for winter

We used these during the 2011/2012 and 2012/2013 winters and had dry hives in the spring. In a few cases there was a bit of dampness in the ventilation box. It was a big improvement, but we were still reliant on small upper entrances.

Improving insulation and switching to bee-sized hives

The trouble with insulation when it's wet is that it becomes less effective. I learned that in the warré hive design a quilt is typically placed on top of a top-bar cloth and is left on the hive all year long. Once the bees propolize the cloth, moisture is no longer able to be absorbed by the quilt, instead the quilt just serves to insulate. There isn't really any attempt to absorb water.

With my initial experiment with a warré inspired design I noticed the bees also looked very cozy in their little boxes. Even a smaller winter cluster is very likely to have bees touching all four walls of the hive. I believe this could be an important factor that allows a colony to better control the humidity within their hive. Dennis Murrell noted in his experiments that smaller clusters are more susceptible to moisture problems.  I have also discussed with a large scale beekeeper who felt that an upper entrance wasn't as necessary when squeezing colonies down into a single brood box for winter.

Temperature Swings

Another idea kicking around in my head, that I do not have much evidence for, is that insulation might also help prevent moisture problems by preventing the hive from warming up too quickly. If condensation does form, and freeze at the top of a hive, perhaps the bees can simply drink it up if it doesn't melt too fast. Maybe winter moisture is even a resource that they can invest into brood rearing.

Matt at beethinking.com has some data on the use of a quilt on a langstroth showing how its use stabilized temperature fluctuations in the hive.


So I started using a hive very similar to the warré style. I built them with thick cedar walls, I place a quilt on them all year long, and I do not provide any upper ventilation.

2013 / 2014: was a particularly cold winter. The first year using warré hives with quilt boxes placed on top of propolised top-bar cloths. I checked the bottom of a few quilt boxes several times over the course of the winter. Though I didn't find any  moisture build up, it was interesting to discover that on warmer sunny days, the temperature at the bottom of the quilt box would be a few degrees below ambient.

2014 / 2015: Another brutally cold winter. One colony had been blown over during an intense wind storm in early November. In the frantic process of putting the hive back together again, the proplized top-bar cloth was removed. The hive overwintered with only the quilt directly on the top bars. In the early spring the upper 3/4 of sawdust and straw was a little damp as was the roof. This was replaced with fresh dry material.

2015 / 2016: I successfully overwintered 9/9 warré inspired hives. Overall, it was a shorter milder winter then normal for Ontario, but we did see a few days with very frigid temperatures. I did see liquid on the bottom board from time to time, but very few bees died in the hive, and there was no evidence of moisture impacting the bees.

2016 / 2017: Another mild winter. Unfortunately, seven hives at one location were vandalized and died as a result. 2/2 hives at another location, not only survived, but were ridiculously strong in the spring.

2017 / 2018: Mild fall, but a real cold Canadian winter followed by a freezing spring. 6/6 colonies survived. After five years of doing this I think it's safe to say this is no longer a risky experiment anymore. It's official. Honeybees do not need any upper ventilation in Southern Ontario if properly prepared.

In two cases quilt boxes were mildly damp. I attribute this to an older top bar cloths, one that had a very tiny tear and one that left a miniscule gap at one corner. One hive a bit of mold on the top bar ledge of a lower box (suggesting some condensation formed below the cluster). Overall they were strong vigorous colonies ready to jump all over the first flowers when they finally arrived at the end of April.


The Biology and Managment of colonies in Winter

This excellent document from the Canadian Association of Professional Apiculturalists provides a quick and clear overview of honey bee behaviour over the winter months including changes in the hive correlated to specific temperatures.

The graph of colony metabolic rate seems particularly useful for estimating honey consumption over the cool months

After hearing a variety of ideas on how this years mild winter might have affected the bees it was nice to find some quantitative data on the subject.

It also offers some thoughts on dealing with moisture in the hive and comparisons of solar versus insulated hive wraps for winter.