bee biology beekeeping equipment ventilation

Ventilation Part 1: A hive is not a tree

How much ventilation to provide a hive of bees is another of those controversial issues that spans both winter and summer beekeeping. More often than not it seems that the “old-timers” are against adding ventilation, while the “newbees” are for adding more and more.

Whenever I try to assess a biological problem, I like to start by looking at how the situation is handled in nature. With that in mind, I started looking at the ventilation bees provide themselves in the wild and compared it to the ventilation in a hive. As it turns out, the two situations have very little in common, and so it is very difficult to translate conditions in one space to conditions in another.

Bees that live in the hollow of a tree frequently have no top ventilation. The cavity may open for some distance above the cluster, but at some point it is closed off. Based on this, many beekeepers think top ventilation is unnecessary.

But a tree is very different from a hive. For one thing a tree has more mass. More mass means there is a greater thermal buffer to fluctuations in outside air temperature. I know I’m not saying this like an engineer would, but a thing with lots of mass does not change temperature as quickly as a thing with less mass. For example, if you take a slice of bread and a hamburger patty out of the freezer and place them on the counter, the bread will thaw a lot faster because it has less mass.

The mass of the tree is a lot greater than the mass of the milled lumber that makes up the hive body, so the bees in the tree are more protected against rapid fluctuations in air temperature. This insulation means that condensation forms more slowly.

Also, the condensation that does form may be absorbed—to some extent—by the tree itself. A cavity in a tree may contain rotting wood or punky material that actually soaks up the condensation like a sponge and prevents the moisture from dripping down on the bees. Bees handle the cold quite well, but cold and wet is a deadly combination.

Another thing I’ve noticed is that the one opening the bees have in the wild is usually larger than the tiny winter openings we traditionally give our bees. Openings are often 3 or more inches across in the wild, or they may be long and narrow slits. In either case, they allow substantially more air exchange than the ½-inch by 1-inch opening we often provide.

What I conclude from these observations is that we can’t compare a hive to a tree. Instead, we have to compensate for the short-comings of our hives and make them do what a tree can do naturally.

The biggest shortcoming of a Langstroth hive is its inability to buffer the temperature changes which cause large amounts of condensation to form—condensation that has no way to get out.

As humans, we spend a lot of effort to get rid of excess moisture in our homes, our buildings, our cars, our factories—everywhere. We know that excess moisture is bad for human health, animal health, and the longevity of material goods. We know the excess moisture facilitates the growth of molds, fungus, and pathogenic organisms. Shouldn’t we apply what we know about excess moisture to our bees? Don’t we owe them that much?



  • Aren’t there certain types of hives that have absorbent layers of wood shavings and stuff in them? I was reading something about this recently, but maybe the language barrier thwarted me. The condensation really does concern me. I want a tiny, doll-house sized dehumidifier for my hive, but I suspect that they would build comb on it and clog the intake/output vents.

    • Yes, they are called Warre hives. I plan to write about them in Ventilation Part Later. They’re pretty interesting.

  • Nice analysis. I am a 2nd year beekeeper running Langstroth hives with screened bottom boards in Central MA. I haven’t had problems with condensation even through the winter (I left the SBBs in over the winter). All my hives made it through the winter. Also I saw some chalkbrood on some frames of a hive I started from a nuc I bought, but it went away the next season (I blame the chalkbrood on the sealed bottom of the nuc…).

    I think I’ll always run SBB bottoms…

  • In my toiling with removing bees from various types of structures, I have found a couple other differences in hives built for bees by humans and places bees like to set up their colony. The first is the lack of maintained space in buildings and cavities that the bees will willingly colonize.

    Several building removals I have done have revealed the lack of maintained combs in very large multi-year colonies. Most older combs are highly prone to pests such as wax moth and SHB. During the late summer and fall, most large prosperous colony populations contract quite considerably, leaving highly exposed combs that are not patrolled or occupied. These unoccupied combs become prey for apiary pests and become part of the sometimes massive debris that plague healthy colonies. These debris piles can become extremely overwhelming on the colony and in some cases cause the colony to abscond the following spring. A maintained hive can have the unoccupied frames removed and stored for the following season without danger of becoming prey to wax moth and SHB.

    I have also noticed that some buildings also cause additional moisture build-ups. Trees, for example, have the ability to respirate a certain amount of moisture from their core. Painted boxes become moisture retaining vessels, often rotting from the interior out, leaving a thin shield of paint. Hive bodies can be ventilated with SBB and ventilating tops.


  • Dear Rusty,

    I have found my favourite bee site – thank you!

    I inherited one overwintered hive & 3 empty ones this spring when the previous beekeeper moved away & abandoned them. The owner of the property I work on (landscape designer/gardener) asked if I knew anyone to take them over, to which I answered “well, there’s me…”. He bought me a bee suit & gloves, and I have bought a smoker, hive tools, additional supers, etc. Also bought a queen & package on May 2nd, & got lucky & had a swarm move in to 2 boxes I’d set up (with some comb & honey), so now I have 3 hives, and a few spare deep boxes & frames.

    The one overwintered colony is set up with a bottom board, a deep box, a 6″ super (with comb), then a queen excluder & 2nd 6″ super, inner cover & top. It’s sited next to a lavender field that is just bursting into bloom (lavandula x grosso).

    I inspected this hive today & found that the 2nd level is pretty full, brood & honey building up on all except the outer frames, with bees above the queen excluder, but no real build up of comb there. I’m anticipating there will be a massive amount of pollen available from the lavender for the next month or so. The property is on 16 acres by the SF bay, and there are also extensive gardens & woodland/grassland/wildflowers there – hopefully, bee paradise.

    My question is: Should I have started with 2 rather than 1 deep? Is it too late to add another deep if so, in which case would I put it as the new bottom box? That would give me the chance to add a slotted rack & screened bottom in place of the standard plywood one and also give the bees 2 deep boxes to get through the winter. I’d be prepared to remove the queen excluder & 2nd super if that seems a better set-up for the bees.
    There were some wax moths in the abandoned frames, the worst of which I scraped down to the foundation: will the bees take care of any larvae I missed?

    I’m pretty new to all of this, but learning lots from your site. Incidentally, the package is also doing fine (in 2 deep boxes) on the property above (50 acres), and the found colony is thriving in the Sierra foothills (2 deep & 1/6″ super.

    Thanks again for such a wonderland of knowledge.


    • Andrew,

      Beginning with one deep is fine. I like to add another deep when seven or eight frames are drawn and full of bees. Most people add the new boxes on top, but there is nothing wrong with adding them underneath if you want. It’s a little harder to check on their progress, but you can do it.

      You don’t really need a “chance” to go in and add the slatted rack and screened bottom. You can do it anytime and it’s not that disturbing to the bees to just lift off the box, change the bottom, and put the box back. It will only take a couple of minutes.

      The bees will take care of the wax moth larvae as long as the bee population is strong. Too much empty space above the bees is not good for wax moth control, so keep the interior size commensurate with the size of the colony.

  • Hi Rusty,

    I’ve been to a talk based on mass ratio of beehives and the replication of the thermal insulation of trees. Done by a physicist writing a PhD on it. Seems many of the solutions we use (ventilation, quilts, etc) to solve the shortcomings of langstroff hives, as you’ve said above, and are treatments for symptoms of a problem that could be treated with insulation. This is something I’ve misunderstood until now and am very pleased to find you’ve touched on the subject. If I can get the journal article I’ll let you know what it’s called.

    Not sure how I’ll go from here as I’m kind of in love with the entrance per box idea but that is difficult with a highly insulated hive. Maybe a bit of both.

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