Winter survival of honeybees is one of my most frequently asked questions from people curious about bees. With the extreme cold temperatures hitting most of the East Coast, this topic has come up again and again.
A healthy full-size colony, with an adequate supply of honey, and a strong healthy queen, can survive extreme temperatures. Adequate honey stores can range from 40 pounds in southern states and 80-90 pounds for northern states. For me in the central part of the east coast in Maryland, it falls in between, around 60-70 pounds.These are averages only. If we are hit with extremes like we have had in the past couple of weeks, you need additional honey stores.
According to Mann Lake a full ten-frame deep yields 80-90 pounds of honey, and a full ten-frame medium yields 65-75 pounds, so I need at least a medium box full of honey for my bees to survive.
I woke up this morning to -1 below zero F and have friends in Massachusetts who were -23 below. That means the bees are ripping through their stored honey at a much faster rate than average. So, I am concerned as my hives going into winter weren’t as strong as I would like.
At those low temperatures, very small populations can’t stay warm, especially since today’s high is only 18 degrees F. Any marginal hives that you were hoping to get through the winter can’t produce the heat necessary for survival. But a large, healthy hive has the cluster numbers to maintain the necessary temperatures to survive.
When air temperatures hit 57°F, the honey bees start forming their cluster on a frame with some honey present. And when temperatures drop to 23°F or below, the bees on the inside of the cluster begin vibrating their wing muscles (fanning) to generate heat, which aids in bringing up the internal core temperature of the cluster. The outer shell of bees of the group are motionless, acting as insulation. The inner bees who are vibrating their wings continuously trade places with the outer bees so they can get warm. The whole process is like a swarm that leaves the hive to gather on a branch. The queen is in the center and the inner bees constantly trade places with the outer ones to maintain the temperature necessary for hive survival. The cluster is a device for protecting and insulating the queen from any harm.
Does wrapping really help? There is controversy about wrapping/vs not wrapping. A wrapped hive just means a layer of black roofing felt is placed around it which takes advantage of solar gain on sunny days. Wrapping doesn’t do much to prevent heat loss but on a sunny day it can raise the temperature inside the hive a few crucial degrees. This could enable the cluster to move closer to honey stores and avoid starvation. Wrapping also helps seal out harsh winds. Although the bees seal up the joints between boxes with propolis, when you manipulate the hive bodies, this seal is broken.
When there is brood in the cluster, the bees maintain the center at around 90 to 95 degrees; without brood, the cluster core is closer to 70 degrees. The outside edges of the cluster are kept at around 41 degrees.
Some people cover the entire hive in foam board for insulation. Insulating can buffer a hive but can also lead to moisture buildup inside the hive which can rain down into the cluster on a sunny day, killing it. Some moisture is good inside a hive as humidity, which is lacking in winter, and needed by the cluster to stay healthy. But too much moisture is detrimental. I prefer a good windbreak near the hive of either shrubs and trees or a physical one like a building or something as simple as setting up plywood to lessen the wind force. And talking about wind, be sure to place something heavy on top of your inner cover to weigh it down.
The best scenario for extremely cold temperatures is snow insulation. Just like winter plants, snow insulates the ground and they have better survival rates than if there were simply bare soil.
The best instructions that I seen on wrapping/insulating your beehives is at How to Wrap a Bee Hive for Cold Winters.
For feeding bees in winter, go to my post Feeding Bees-Keeping Your Hives Alive! Directions are available for making candy fondant to add to your beehives for supplemental feeding during the winter.