Once upon a time two colonies of honey bees decided to spend an autumn weekend away from the suburbs. They packed their tents, sleeping bags, and plenty to eat before they took off into the foothills. One colony went into a sheltered valley. The other colony flew up to a wooded ridge.
Before the first colony pitched its tent, rain soaked everything. Their sleeping bag, tent, food supplies, and even their wings were drenched. But with daytime highs in the 60s and nighttime lows in the 40s they weren’t too worried; after all, they wouldn’t freeze. But the rain had chilled them, so they closed up the tent as tightly as possible so no more cold air could get in. They huddled together inside their wet shelter—cranky, miserable, and too cold to eat.
Their friends higher up didn’t get wet at all. Everything inside the tent was dry. Still they worried about the weather—with daytime highs in the 40s and nighttime lows in the 20s—they knew they had to be prudent. So they opened the ventilation flap to prevent their breath from condensing inside the tent and snuggled warmly together beneath the star-studded sky telling wasp stories and drinking honey wine.
By morning, many of the bees in the wet colony had died of hypothermia. Those remaining were too cold to move, even to get a bite of breakfast. Those that could move at all could barely put one foot in front of the other. Their blood sugar dropped from lack of food and they stopped thinking or even caring. They became disoriented. More would die before the weekend was over.
Up the hill, frost rimed the twigs and the sun glinted off the ice crystals. Inside, the colony laughed, stretched their wings, and shared breakfast. They had enjoyed a spectacular night and were now rested and eager. . . .
Keep ’em dry
Okay, I’m guilty. Once again I have personified the bees. But there is a lesson here. Would you, a human being, be better off in a wet 40-degree sleeping bag or a dry 20-degree one? It’s really no contest—and bees are the same. Dry bees can survive very cold temperatures, whereas wet bees collapse quickly. If you have a soggy hive with water dripping from the roof onto the cluster, there is a good chance they won’t make it through the winter.
Evaporation is a cooling process, so as water evaporates we feel cold. If you get out of a pool or out of the shower, you feel the chill almost immediately. But conduction also plays a big role. Water is much denser than air, so water draws the heat from your body much faster. If you wrap yourself in a wet blanket that is at room temperature, you will feel colder than you would without the blanket at all.
When humans experience a drop in core temperature they lose the ability to control their muscles and ultimately lose their ability to reason. Honey bees are similar. And even if your bees survive the cold temperatures, a wet hive is a culture plate for fungus and molds, and a breeding ground for a number of pathogens, especially the brood diseases.
It is true that the amount of humidity in a hive is influenced by a number of factors, including the hive type, size, climate, and local weather patterns. But if you open your hive and find water inside the roof, under the inner cover, or collecting on the top bars, your hive is suffering from moisture overload and needs ventilation. No one is healthy living in a dank, humid, dark, moldy, airless box—not even honey bees. Plugging every hole to keep out the cold could be the worst thing you ever do for your bees.