Moisture Control in The Hives: A Four-Season Approach
How Honey Bees Regulate Temperature and Moisture
Reading Time: 5 minutes
Temperature and moisture regulation in the honey bee hive is a collaboration between the honey bees and their beekeeper. We work with the seasons and the bees’ own incredible ability to self-regulate to keep heat, cold, and moisture in check. While it is useful to look at how bees live “in the wild” to understand their natural preferences, it’s good to remember that honey bees are adaptable and live all over the world, in all climates. They live in straw skeps, in clay pots, in stone walls, or wooden boxes. They live in caves or hollow trees. They thrive in the desert, overwinter in the frigid north, or live on rainy coasts. In the US, many bees are moved across the country following blooms: they are able to adjust to multiple climates and locations per year.
Most of us in North America use standard Langstroth hive equipment. For this reason, I’ll talk about managing moisture in Langstroth hives. There are countless opinions on moisture control in beehives, and countless equipment modifications to be experimented with by experienced beekeepers. I’m writing from the perspective of a Minnesota beekeeper, which I am. We usually experience warm, humid summers and long, cold winters, followed by wet springs. Your local climate (and your beekeeping equipment) will greatly affect how you manage your bees, but the basics of how bees regulate temperature and moisture should be relevant anywhere. Let’s talk about summer first.
Bees use a few techniques to keep the temperature of the brood nest consistent—about 95 degrees Fahrenheit. If things get too hot in there, bees will fan their wings to circulate air and lower the temperature. Foragers will collect water droplets and place them just inside the hive entrance or on the combs; then workers will fan their wings to evaporate the water droplets into cool air that circulates through the colony. On especially hot days, when fanning and evaporating water isn’t enough, older bees will leave the colony and “beard” on the outer walls of the hive boxes, decongesting the hive so that the younger bees can more easily regulate temperature and keep the sensitive brood from overheating.
Our job as beekeepers in hot, humid conditions is to make sure bees have proper entrances for their large summer populations — both for foraging and for ventilation. An upper and bottom entrance allows for good airflow. Some people use screened bottom boards or screened inner covers for additional hive ventilation in summer.
When fall comes along, populations diminish, and robbing behavior increases, an entrance reducer can be added to diminish the area bees need to guard. Upper entrances can also be plugged or diminished. If the robbing season (August and September in Minnesota) corresponds with very hot weather, you can use robbing screens instead of entrance reducers to maintain good ventilation.
Now to prepare for winter. When temperatures are at approximately 55 degrees or lower, the bees will cluster on the honeycombs, shivering their flight muscles to stay warm. They do not heat the hive structures in which they live. The inside temperature of the Langstroth hive boxes is essentially the same as the outside temperature, though the walls provide protection from the elements. The bees only heat their own cluster of selves. The thick, outer layer of bees is tightly compressed; essentially, the bees make themselves into their own insulated coat — each bee, a stitch. The center of the cluster is about 85 degrees; it reaches approximately 95 degrees in late winter when the queen starts laying eggs again. While we think the bees rotate from the outer layer to the inner part of the cluster (taking turns being warm and being almost-comatose), we know the queen is always near the center; always warm. Once brood is being raised, the bees’ ability to regulate the hive temperature is of the utmost importance: chilled brood, just like overheated brood, will die.
All winter long, the cluster expands and contracts, adjusting its density and temperature as the air temperature around it shifts. On warm days, the bees break their cluster formation, take cleansing flights, and move to new areas of honeycomb. Clustered again, wet air rises off the of respiring, metabolizing bees and, hitting the cold air, produces condensation.
That condensation gathers on the hive walls and inner cover, and can drip down on the bees, and kill them. While honey bees can withstand frigid temperatures (provided they are healthy, have low mite levels, and have enough food), being cold and wet can kill them. Beekeepers in cold climates can add a piece of particle board or other absorbent material over the inner cover to wick condensation out of the colony and avoid death by wetness (some beekeepers use wood chips or newspaper instead of particle board). A small upper entrance — either a notched inner cover or a hole in an upper box — will allow for ventilation and cleansing flights when hives are half-buried in snow.
While it doesn’t provide heat, a black, waxed cardboard winter-cover, Styrofoam siding, or plastic “bee cozy” can provide some insulation to make the bees’ job keeping themselves warm a bit easier. Insulation becomes especially helpful when the bees begin rearing brood in late winter and early spring, as they will ramp up the cluster temperature significantly.
In very early spring, when temperatures begin to inch up, things can get pretty wet for us in Minnesota. That moisture board (or moisture quilt) above the inner cover remains essential for our bees. Early spring nectars are yet another wet element that is introduced by foragers into the colonies. Too much moisture encourages mold and the fungal disease chalkbrood. It’s partly a matter of waiting until the weather dries out (bees can handle mold, and chalkbrood often clears up by late spring or summer). But variable spring weather means that bees will still be clustering on and off; no need to remove moisture boards until the warm weather seems here to stay.
It’s incredible to witness how honey bees live in climate extremes. How they shiver all winter long in the cold. How they hang lazily outside the hives in the heat summer, in order to keep the brood from overheating. How in spring some seasonal impulse or slant of light provokes them to begin their brood rearing again … but honey bees do need us. They need us to study their biology — their natural ways of living — in order to help them thrive in our human-designed environments. Once you understand the basics of moisture and climate control in your hive, there’s endless equipment, hive set-ups, and insulation choices to experiment with.
Will you tinker with your hives equipment this season, and how?