[Bonus] Short - Dewey Caron: Condensing vs. Ventilating Hives

[Bonus] Short - Dr. Dewey Caron: Condensing Versus Ventilating Hives

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Dr. Dewey Caron: Hi. I am Dr. Dewey Caron. I come to you from Portland, Oregon, following my return from Apimondia in Copenhagen, Denmark, in the Washington State annual meeting. I present another audio postcard on communication in my continuing series of once monthly Beekeeping Today Shorts podcast. Topic this month, October, is condensing versus ventilated hives. For these audio postcards, I have been discussing communication on three levels: Bee scientist to beekeeper, beekeeper to bee, and bee to bee.

We'll start with bee scientist to beekeeper. I referenced studies by an engineer, Derek Mitchell, who has studied the physics of the modern beehive. His thesis, if you're interested, the University of Leeds in England, is Differences in Heat Transfer Between Man-made and Wild Honeybee Habitats Using Computational FluidDynamics. Quite a title. I also will reference Tom Seeley, who has examined both feral hives, bees that are living in trees where, of course, they are unmanaged, and bees in managed Langstroth hives. Tom, of course, is coming from his perspective as a biologist.

Derek's studies of the thermal properties of cavities cast out on the long-held assumption that the behavior of clustering is normal bee behavior, something very natural. He believes it's an indication of stress in bees during the winter, or at least as he has studied them in the modern Langstroth hive.

Conventional wisdom has been that beekeepers should avoid the accumulation of moisture at the top of the colony during winter. We need prevent droplets of condensate moisture forming at the top of the hive because it can rain down onto the bees and their cluster. Moisture falling on the insulating outer bees of the winter cluster creates a cycle of bees getting wet, so the bees then need to move to dry off. This movement results in the usual insulating mantle of what should be tightly packed workers becoming less effective, allowing even greater escape of the warm air from the middle of the cluster, kept around 95 degrees, more water droplets forming, resulting in even more droplets raining back down on the bees.

The concept that moisture is detrimental to a successful colony overwintering dates from Langstroth, patenting of the hive that we use, the Langstroth hive. Of course, that is used by at least 90% of beekeepers. There are some other hives as well. Basically, they may have different dimensions, but basically are moveable frame hives, almost, except for something like a top bar hive.

Tom Seeley and others have described bees overwintering and bee trees. A bee tree has one single entrance, usually near the bottom of the comb area. For large openings, the bees use propolis to reduce that large opening to a smaller one. The bees line the interior surface of the cavity with propolis. There's no upper entrance or provision for moisture escape. Wintering populations are typically small since there is a smaller physical space where bees are inhabiting and therefore less beeswax comb in that typical feral nest, partly due to its smaller size.

We can take our clues of what bees need in our conventional beehive from how bees overwinter in the wild. Bees in Northern Europe countries naturally have evolved to live in tree hollows. What might they communicate to us? Scout bees from swarms investigate several potential cavities, according to studies by Tom Seeley. His studies have demonstrated that cavity selection by bees involves several selective features such as cavity size, location, entrance size, and opening orientation, among other factors.

The bees use dance language to inform others of their site find, and favorable site dancers stimulate others to go and investigate that same location. They, in turn, return to form yet more bees with their dancing. The selection of where to locate is a consensus among the scouts. They give the message to the clustered swarm to leave the bivouac site. Once selected and inhabited, the bees engineer parallel beeswax comb for brooding and, of course, food storage.

Success is not great for such colonies, with around only about 20% successfully surviving the initial winter. It all depends on size of the swarm that moves in, size of the cavity, and time of the year, of course. It's a risky behavior to leave home and build a new home in a new cavity. How might this apply to our modern hive and how we manage it? How do we communicate with our bees? Two distinctions in our management choices to assist in successful overwintering of our colonies in the hives that we put them in are the condensing hive and the ventilating hive.

Other wintering managements we might employ include control of pests, such as mice or other small animals that might seek a beehive for winter shelter, addition of some insulation to the hive sides, selection or modification of a site, such as putting on rain shelters, hay bales to reduce wind effects, et cetera, and closing of a screen bottom board, if one is being used.

The condensing colony means adding insulation at the top of the colony and closing upper vents to avoid cold air drafts and loss of heat. The idea is to hold a heat pool at the top of the colony to help warm the overwintering bees and keep the upper surface warm enough to avoid droplets of water forming on it. The bees don't need to generate as much heat to keep warm. The heat pool helps them keep that warmth, whatever the outside temperature.

When the heat pool is below the dew point, warm moisture-laden air doesn't form as droplets at the colony top. Instead, it is distributed to the sides and subsequently circulated downwards as it heat cools, as they reach cooler temperatures and it cools, that warm air cools. On the coldest day, it might appear as frost at the side of the box. Bottom boards may accumulate some of the moisture as it cools at the sides of the colony and as it is falling from the top of the box. The water even can be used by the bees. Water is critical for them. The opposite condition to a condensing colony is a ventilating colony.

Condensing colony has three distinctions compared to a ventilating colony. One, the condensing hive has lots of top insulation. Top insulation means moisture-laden air shunts to the side rather than forming as moisture droplets at the colony top. Two, the bees control ventilation, circulating fresh air to avoid CO2 buildup while conserving heat and humidity, versus the beekeeper doing it in the ventilating hive. Three, the beekeeper provides a single colony entrance near or at the bottom of the comb that is usually reduced in the size of the opening and without any top venting or any moisture-trapping device.

In contrast to that condensing colony, the ventilating colony involves adding ventilation to bee boxes so moisture-laden air is vented from the top of the colony. There is an inner cover notched to provide moisture escape, or additionally, beekeepers commonly drill holes in hive bodies above or to the side of the handhold. Some may remove the covers to scrape the propolis as their last late fall visit to aid ventilation. Some even add a wooden shim or a carpet tack or a small stone or stick to help vent the top, the very top of the hive.

Common wintering management for individuals who are concerned with moisture during the overwinter period is to add a quilt box or ventilating device. One of our Oregon bee supply dealers calls this a Vivaldi board. There are a number of names for it. This is placed at the top of the colony to capture excess moisture. Individuals using this will place wood shavings, straw, burlap, old terry towels, athletic socks, absorbent materials to absorb that moisture above the wintering bees within this added device. Screen side vents are provided to shunt the moisture captured by the absorbent material to the outside.

One uncommon convention was using solar panels to power a ventilating fan at the top of the colony, as I described for one Oregon beekeeper. If colonies are populous enough and the top venting of moisture does as expected, and the bees can reclose the draftiness to reduce the escape of heat in the top box, the bees will survive until spring. Adherence of both condensing and insulating hives, they're providing the best means to assist their bees to successfully overwintering.

Providing an upward bee entry exit is recommended in areas of heavy snow cover if the lower entrance is likely to become blocked with snow or become iced in. In addition to venting moisture-laden air, the bees can use the upper entrances for mid-winter cleansing flight to avoid accumulated feces. They don't need to walk to the bottom box to use the bottom entrance, but an upper entrance, depending upon location and if not propolis closed, might also vent heat and moisture from the hive.

The potential downside of upper entrances is that they can create a constant cold air draft movement through the boxes from the bottom entry of colder air, heating of the air by the bees and their cluster, and then escape of warmed air from the top of the box. Bees need to replace the heat. More honey is then needed to enable the bees to run their wing muscles that produce that heat. The greater the heat loss, the more heat that needs to be generated, i.e., the more honey needs to be consumed. A minimum of R5, R as a measure of insulation value, or R10 at the top of the colony, is sufficient to reduce heat pool loss and keep warm the first upper surface where water droplets might form.

Bees within the heat sink need to generate less heat, rather than it being vented to the outside of the hive. A one-inch thick extruded polystyrene, what we call XPS foam board, provides a R5 insulation, a one-inch piece. Cut the ventilation to tightly fit inside the telescoping cover or place it within the quilt box, covering the screen sides. Use tape to close any edges and any cuts that you make, since bees will not have access to use propolis to this area.

If you have an insulating hive, there's no need to insulate above the moisture-accumulating area. The trap moisture negates insulation above it. You're not going to need any insulation above it at all. In fact, that was going to be contrary to what you want to do in capturing the moisture and have it vented.

What else might we do to help our bees overwintering? One time, beekeepers wrapped colonies for protection of their bees during winter. Some still do. Wraps to cover the outside of the hive included tar paper, wood, plastic, styrofoam, any type of material that will provide insulating value. Beekeepers at one time placed another wooden outer box over their hives in the winter, adding straw or wood shavings between inner box and outer shell. These would be removed in the spring and stored the rest of the year.

The original Langstroth hive was a double-walled hive. Today, plastic hive bodies are increasingly common. One of the advantages they provide for a better insulated hive. However, the majority of the heat potentially lost by clustering bees in the winter is at the top of the hive, not the sides. A hive design that better insulates both the sides and top of the hive will pay the biggest dividends and better survival.

Smaller boxes in colonies with smaller populations, such as overwintering of bees and nucs, need more attention for overwintering. Adding insulation at the top and sides and provisions of adequate stores, even the addition of a sugar candy cake, will promote better success with overwintering of nucs and colonies with a smaller adult population. As for the bottom, if you use them closed screen bottom boards, if winds can whistle beneath your colony, a dead airspace is fine. You do not then need to close that screen bottom.

Another device is the slatted rack. A slatted rack between the bottom board and the lowest brood box helps bees ensure that they set up for their winter cluster within the lowest box, using the division between the two boxes as their communication from one frame to the next. Honey-filled frames in the top box will help provide insulation and hold a heat pool to benefit the bees.

When bees reach the top interface, which will eventually occur as they eat the honey from the frames, they are telling us something. We and they are better served if honey remains in the top portion of frames of the top box into when we start doing our spring management. A condensing hive more closely resembles the natural bee nest in a tree. Consider top insulating to ensure warmer and cozier overwintering bees. Good luck with wintering, whatever your choice of management. I provide some of the sources that might help you in your decision-making.

Finally, let's consider communication of bee to bee. What do we want to communicate to our overwintering bees? It is true, there's no one right way to keep bees. The best way is one that works best for you. Should we ask the bees if they prefer a condensing or a ventilating hive? You can. You can set up both types in your apiary. Is clustering actually a manifestation of stress for our bees?

We have adapted our wintering to follow Langstroth's suggestion to take losses in the fall and overwinter only the most populous colonies for a successful outcome in the spring, colonies that are fat, fat with stores, as well as the fat bees themselves. Bees continue to rear brood during the winter. The humidity needed to rear brood, especially after the winter solstice, is provided by the thermal regulatory cluster.

Nurse bees, which provide the larval food, might be in short supply as bees reared in the fall in their colony age. The food pool at the bottom of the individual cell, the pool that's provided by the nurse bees, helps provide proper cell humidity for that developing bee. It is conserved by nurse bees moving from cell to cell. Later in spring, there will be an imbalance of nurse-age bees as the older bees die at a rate greater than they are replaced with newly emerging adults.

One of the fascinating occurrences that might happen in an overwintering bee colony is heater bees. Heater adult bees enable developing larvae in the coldest of winter pass through normal development time. This, however, will shorten the lifespan of the heater bee. Jürgen Tautz introduced us to heater bees in his 2008 book, The Buzz about Bees. Using temperature-sensitive film, Tautz found that some nurse-age bees are able to raise their body temperature about 10 degrees C, which is higher than normal. Bees do this by rapid muscle contractions of their thoracic wing muscles.

Heater bees compress their thorax against the top of a developing capped pupae to keep it warm, but also heater bees enter headfirst into unoccupied brood cells adjacent to cells with developing pupae brood. The heater bee remains about 30 minutes, at which time their body then cools to a more normal temperature. A heater bee using empty cells surrounded by capped pupae is even more effective at distributing heat to help ensure that there are successful bees emerging for the next generation.

Tautz specializes that worker bees can assess the state of the highest population. Honeybees, like a host of other animals, are sensitive to temperatures during their development. By transfer of the adult body heat to developing pupae, after determining what types of bees are most needed in the colony, in other words, the younger nurse bees, they can help produce these types over bees that will age in a normal process.

How might this be communicated from bee to bee? In a wintering cluster, the temperature of mantle bees will be much cooler, but the center of a cluster, the temperature is kept at the brood-rearing range. While developing brood generates some metabolic heat, it's not enough on its own. Thus, we see during the year, for example, that the brood area has a mantle of one or more adult bees, busy nurse bees feeding and tending the growing larvae, and gathering over those pupal cells. That population is in short supply in the spring. Heater bees can help supply critical heat to ensure the colony has new bees.

While eggs and larvae in uncapped cells can tolerate brief cooling, pupae and capped cells are highly sensitive to temperatures being too warm or too cool. We know pheromones help regulate rearing a brood. It is speculated that pheromones produced by the developing brood itself can signal when they are too cool, prompting workers to provide warmth. The communication of bee-to-bee is from brood, the developing stage, to the adult bee, which then may become a heater bee.

What is your plan to assist your bees to overwinter? Insulating the hive, providing top insulation, the condensing hive option? What else do you do? We can make a difference. We most likely need to do so to improve survival, especially to overwinter nucs and smaller colonies. I wish you well this winter. Until next time, be well.

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