honeybee wintering

As the days get shorter and the temperature beings to drop, bees and beekeepers alike turn their attention towards one of the biggest challenges hives face all year: honeybee wintering.

In warmer, more temperate regions, this can be a gentle slowdown, with chilly mornings turning to sunny days and hives still able to forage or produce brood. But in colder parts of the world, this can be an anxious time of year even for advanced beekeepers.

It is true that honeybees will prepare their nests for the winter by themselves, but there are things we as beekeepers can do to assist the bees and improve their chances of survival. Below, we cover some of these tips, as well as common misconceptions regarding your hives, and what is going on physiologically in the hive during this critical time of year.

As anyone who has been keeping bees for a while knows, getting your colonies ready for winter does not begin once you see frost…it begins in the autumn months, possibly even late summer when considering honey. When taking honey off it is important to be certain you have left the bees with enough food to survive the winter. In general, an average sized colony will require 45 to 50 KG of honey to make it through a long season. If during your fall inspection, you discover that your colony does not have sufficient honey stores for the winter you can either add frames of honey to the colony, if you have saved some from earlier in the season, or you can feed heavy sugar syrup (2 parts sucrose sugar to 1 part warm water by volume) to the colony to help complete its stores. A warning though, do not feed “light syrup” (1:1 sugar to water) in the fall or anything less than 2:1. The thinner syrup will chill the colony as they are trying to process it to store for the winter because the bees must remove water from the syrup to store in the combs and this evaporation process robs heat from the colony. Heavy syrup can be stored directly into the combs and it will be a welcome compliment to what they can put away in the fall if they are lacking.

As those late-season flows progress, the bees in the upper part of the brood nest will begin to fill cells with honey where worker bees had emerged. Restricting the upper parts of the brood nest forces the queen into lower parts of the colony – the perfect position to start the winter. As winter continues, the bees will move up through the colony consuming the stored honey. When the cluster moves up through the colony the honey above them gets warmed by the advancing cluster.

honeybee wintering
L. Connor Photo

Bees are putting nectar in cells recently vacated by emerging bees.

A typical colony going into winter will have anywhere from 20,000 to 30,000 individual bees. If the colony has fewer than 15,000 bees they are highly unlikely to survive a tough winter, and it might be best to unite weak colonies together, or unite the weak hive with a stronger one. Beekeepers have a saying to this effect, “take your losses in the fall.” If the hive looks weak then merge it with another and remove the queen of the weaker colony. She is most likely the reason the colony is struggling in the first place. Simply putting a piece of newspaper between the two colonies will ease the introduction of the weaker colony (or there are double screen methods of uniting colonies that you can view on the internet).

As the temperature drops below 10 to 14°C, the hive will begin to cluster and the bees tap into those hard-earned honey stores, generating small amounts of heat through muscle activity to keep the cluster warm. With enough bees, and sufficient stores, they are well prepared to survive a long season. Like many of us, they drop the thermostat a bit during the winter months to conserve energy, and when broodless aim to keep the middle of the cluster around 20°C versus roughly 33°C when brood is present. This allows them to stretch those honey stores a bit longer and further reinforces why you want to stay away from any activity that could encourage brood production during the winter months or result in them breaking cluster.

When I was first learning how to keep bees, we were taught that the cluster was a very democratic living space. It was believed that chilly bees on the outside of the cluster would then rotate to the middle where they would warm up by the fire before eventually rotating back out to the exterior. If anyone else was taught this, I hate to be the one to burst your bubble…but we have since learned that this is most definitely not the case. Bees on the outside of the cluster are physiologically designed to be there.

Those chosen to be on the outside begin to produce a level of glycol in their bodies by metabolizing sugar that allows them to withstand extreme cold without their cells freezing. These lucky bees act as insulation to the cluster, and that glycol in their hemolymph can be turned back into sugars and heat eventually. Worker bees can literally turn their blood into antifreeze. Pretty neat, huh?

But this is not the only physiological change your bees make. Arguably the most critical piece to winter survival in harsh climates is ensuring you build “fat bees.” You hear this term thrown around a lot, but what does it actually mean?

The simple answer is that it refers to a winter bee with a lot of stored fat (also known as vitellogenin) in her body. Vitellogenin is a lipid, protein, and carbohydrate complex stored in the abdomen that acts as winter stores in the bee’s body. You see, bees not only store resources in the hive but they also store protein and carbohydrates in their bodies as well, think of a bear going into hibernation. How are fat bees produced you might ask?

As the season shifts to autumn, day length decreases and the queen begins to slow her egg production. This causes a shift in the nurse bee to brood ratio in the colony and creates an excess of royal jelly as there are fewer mouths to feed. Before long there are more nurse bees than larva in the colony and the larva that are there are fed extremely well and begin to build vitellogenin because of this surplus of royal jelly. With the queen slowing down her egg production there will be few or no larvae to feed the royal jelly, so the nurses will share the royal jelly with the adult bees in the colony through trophallaxis who then internalize the rich diet and turn it into fat in their bodies. Hence, fat bees.

The other area to pay close attention to as winter draws near is mite control. Controlling Varroa mites is one of the largest challenges beekeepers face today as it is the leading cause of winter colony loss. The deformed wing virus (DWV) has been identified as the main contributor to that winter loss with dozens of other viruses dragging honeybee lifespans down. There are numerous mite control options available, but the important thing to do is to monitor mite populations and treat appropriately. It is critical to keep the mites under control because we still do not have good antivirals for our bees, and varroa is essentially a “dirty needle” vectoring viruses between bees and between colonies. Once the mites are under control, it is advised to feed a protein supplement that will stimulate brood production and get that royal jelly going. Feeding for two brood cycles is typically recommended for fall/winter preparation.

Something good to consider depending on your area could be mouse guards or entrance reducers. The problem with mice (or other critters) in a colony is not necessarily the comb or stores they will destroy, but rather the movement in the colony will disturb the bees and cause them to break cluster and lose heat. Once the cluster is chilled it takes energy to reestablish the brood nest temperature and repeated disturbance by a mouse will surely kill a colony. Reducing the entrance to your hive will prevent these unwanted guests.

In some countries, wind screens or wrapping your hives is common. Ensuring your boxes are in good condition is important as well, but hives are not as fragile as you think. In graduate school I got some firsthand experience with just how hearty bees can be. One of my fondest memories of my time at Michigan State University was morning coffee with the faculty. In a large naturally lit room on the third floor of the Natural Science Building, the Entomology Department faculty and grad students would gather for morning coffee. People would filter in and out depending on class assignments, but there were always interesting conversations being had. I learned a lot at morning coffee. One winter morning there was a discussion of the pervasively cold weather and someone asked my advisor, Dr. Roger Hoopingarner, how the weather would impact the bees and if he had taken any measures to protect the hives from the cold. He replied that if they had enough honey they would do just fine.

He relayed a story about his time in graduate school in Wisconsin when a swarm was established in a hive with only screen wire for sides so the bees were exposed to the winter cold but protected from rain and snow. Discussion continued around the table about how the bees thermoregulate and even raise young under such conditions. After a few moments, Roger turned to me and said, “let’s set that up next spring.” So, with the help of Jose in the shop, we designed a hive that only had screen wire on its sides. The screen wire was to protect the hive from predators who would surely have attacked the bees if not protected. The bees were established in the hive in the spring and the colony prospered during the summer and fall. The hive was in a sheltered area, but as the year carried on it was eventually exposed to the harsh temperature extremes of a Michigan winter.

Periodically I would visit the apiary during the winter to brush snow off the entrances of the colonies and remove dead bees that were blocking the entrance…normal winter maintenance. In early March, I looked at the screen hive but didn’t open it up. I feared the worst, I saw no activity on the frames that were visible. Later in the month we had a day above 10 C and I opened the hive and my fears were allayed. The hive had survived with a cluster about the size of a grapefruit. As the spring wore on the hive continued to grow and was eventually moved to standard equipment but the demonstration was successful. While our honeybees, Apis mellifera, are cavity nesters they have the ability to thermoregulate their cluster and not lose a lot of heat to the environment. Today with thermal imaging devices we can see that temperatures within 10 cm of the cluster are the same as outside ambient temperatures. The bees do an incredible job at insulating and holding heat.

As your colonies begin the transition into late winter and early spring be aware – you haven’t made it out of the woods yet. More colonies are lost in March/April than in December/January due to late season starvation. The bees usually just run out of stored honey and are unable to thermoregulate sufficiently. If in your early season inspections you see a large cluster of bees on and above the top bars this may be an indication that the bees are running out of stored honey. Emergency feeding can be done with something as simple as granular sugar poured on paper on the top bars or you can make fondant or even candy boards to hold the colonies over until nectar becomes available.

If you get some warm days during mid-to-late winter, go ahead and give your hive a check. Fondant or candy can also be applied easily during these inspections if stores are getting low and could buy you the extra time you need to get them through to spring. A warm sunny day of 10 C or higher during the winter is always good for the bees. It gives them a chance to break cluster, move honey around the hive if necessary and go on winter cleansing flights. These cleansing flights are important as the bees try not to defecate inside the hive during the winter. They wait for a warm day when they can go on short flights to rid their bodies of the built-up waste accumulated during weeks or even months of confinement.

While periodic warm days are good for the bees, extended warm periods during the winter can be detrimental to the hive and in recent years these pops of warmth are becoming all too common. Climate change has resulted in far more warm days than was traditional during the winter, and on warm days when the colony can break cluster and fly many of the foragers will be out looking for nectar and pollen, although there is nothing available. These are called empty flights and result in the bees using a lot of their honey stores to look for nectar that is not out there while shortening their lifespans.

In a typical winter, the bees and the flowers are in sync so when the temperature warms up the plants will begin to bloom and bees are ready to take advantage of the resource. However, in the changing climate events we see today, bees are rearing larger brood patterns than normal and flying before the trees and flowers are ready to bloom. This extensive use of resources, combined with continuously breaking and reassuming cluster, can bring on colony starvation and put additional stress on the hive so beekeepers need to pay close attention to what their hives have available as spring nears and be prepared to supplement. When we think of climate change our minds often go to heatwaves, droughts, fires, and other extreme summer events…but we are also seeing more inconsistent winters that seem to be taking a toll on our hives as well. This is something to monitor as we will no doubt see this worsen as we go deeper into the 21st century.

To wrap this all up, every winter is different, and there is obviously no one-size fits all approach to keeping your hives alive during the cold months, but take notes on what worked for you year-to-year and refine those practices. Even the best beekeepers lose hives during winter, so if you do as well don’t get too discouraged. Be sure to ask around at your local bee club for tips more specific to your area and hopefully your hives can get through winter healthy and strong.

  • Take your losses in the fall – unite anything that does not stand a good chance of survival
  • Make sure you leave plenty of honey
  • Control mite populations in advance of winter
  • Feed a quality protein supplement or pollen patties for 6 weeks (two brood cycles) in advance of the queen shutting down to encourage vitellogenin production
  • Consider entrance reducers and ways to limit critters from entering
  • If in a very cold area, consider wrapping your hives or putting up wind screens to block extreme weather if the yard is exposed to harsh conditions
  • If you get warm days mid-winter, give your hives a check and add fondant/candy as needed
  • Pay close attention as spring nears…this is when they stand the highest chance of loss
  • Ask around – other beekeepers in your area may deal with similar issues