Here in Ontario, Canada, it’s warming up and spring is teasing us with sunnier days. This time of year sparks a common question from beekeepers: When should I unwrap my hives come spring? If you’re keeping bees in a cold-climate region, there are several options for helping your bees survive the colder months. If you choose to wrap your colonies over winter, it can be tempting to unwrap before spring has fully sprung—but there’s good reason to keep your bees wrapped until Mother Nature is truly done with winter.
Coping with the Cold
The native range of Apis mellifera, the honey bee most often used in agriculture worldwide, is Europe, Africa and the Middle East. Thanks to human movement (and our love of honey), A. mellifera has been introduced to every continent except Antarctica. This has spurred beekeepers and honey bees to develop management strategies to cope with different climates. Beekeepers use various techniques to help their colonies make it through the winter, and honey bee colonies make obvious changes in anticipation of cold weather.
How a Honey Bee Colony Prepares for Winter
Honey bee colonies take many of their own steps to prepare for winter each year with no prompting by the beekeeper. They store honey, rear winter bees differently, decrease and then cease drone production, and restrict worker brood rearing. As brood area constricts, workers backfill the comb with honey or sugar syrup to last them through the winter dearth.
Cold weather results in the bees convening in a tight cluster surrounding the queen and any brood present in the hive. In general, older bees stay to the outside of the cluster, which will contract and expand depending on the temperature outside.
In late summer, honey bees use environmental signals to trigger the rearing of “winter bees”. This transition is brought on by changes in day length, floral availability, and temperature, as well as internal colony communication, like forager pheromone signals. Worker bees that are reared in the summer have short lifespans and are optimized for foraging, while winter bees are physiologically and behaviourally prepped to make it through the winter. For example, winter bees need to live longer as pollen availability decreases and the rearing of new young workers slows, sometimes ceasing altogether for the winter. Some of the physiological differences of winter bees are that they weigh more, have wider abdomens and enlarged fat bodies (containing lipids and proteins), have more highly developed hypopharyngeal glands, have higher protein, triglyceride, glycogen, and glucose levels, and live 4-5 times longer than their summer sisters.
Beekeeper Techniques for Winter Management
There are many factors to consider when ensuring hives are ready for winter (see our Seasonal Checklist). Food stores, queen status, colony strength, disease and pest management, and insulation are all important. Decisions should always be made based upon the bees’ needs and regional climate. In some regions, doing nothing extra is fine, while in others, beekeepers use specialized buildings with specific heating and cooling, ventilation, and lighting conditions for overwintering colonies.
In between these two extremes lies the option to leave hives outdoors for the winter and insulate them—arguably the most popular option for Canadian beekeepers. Many beekeepers artificially insulate hives when temperatures consistently drop below 13 °C (55.4 °F), the temperature at which bees reduce flying activities.
Although overwintering practices vary by location, most cold-climate beekeepers tend to agree on two broad winter equipment modifications:
- Reduce the lower entrance to minimize pest pressure (e.g., rodents).
- Prepare the hive configuration to accommodate top insulation.
These two simple modifications will help reduce stress on the colony during cold winters, adding extra insurance against winter loss. There are many products available to help get your hives through a tough winter season. NOD Apiary Products offers an affordable, ready-to-use option: Bee Cozy Winter Hive Wrap with Inner Cover Pad, which has been a popular choice for beekeepers for over 25 years.
Colony & Cluster Temperatures
In order to survive, honey bees must maintain specific temperatures: Bees keep their individual body temperature at 15.6 °C (60 °F), but the brood rearing area of the hive must be at 34.4–35 °C (94–95 °F). The outer edge of the cluster is 6–12 °C (42.8–53.6 °F) and the centre, where the queen stays, remains around 33 °C (91.4 °F).
The cluster is in its tightest state once outdoor temperatures reach -10 °C (14 °F). Fuelled by stored honey and syrup, worker bees vibrate their flight muscles to generate heat. Honey bee colonies reach their most efficient metabolic rate at 5–10 °C (41–50 °F) as the least amount of stored feed is consumed at this temperature. Beekeepers who overwinter their colonies indoors in specialized wintering sheds typically maintain this temperature range in their facilities to exploit this tendency.
A Good Reason to Wrap
Most Canadian beekeepers will have their hives wrapped by late fall—but did you know the most crucial time for insulation is late winter and early spring? Following the winter solstice, days start to lengthen, signalling to the honey bee colony that the queen can begin to lay eggs again. The energetic cost of brood-rearing leads to honey stores being eaten at a faster pace than earlier in the winter. Studies have shown that insulated colonies consume significantly less honey and have better winter survival than hives left uncovered.
Did you know the most crucial time for insulation is late winter and early spring?
Conservative feed consumption lowers your overwintering costs and supports your bees with more honey stores later in the season when temperatures fluctuate and colonies are building up. This doesn’t mean you should feed less in the fall, but colonies that overwinter with remaining stored feed will require less supplemental feeding (or perhaps none) in spring. This can mean cost savings and less worry in the spring for beekeepers… a win-win!
Bees Like it Warm
Some new beekeepers worry that leaving hive insulation in place when the temperatures start to increase will “cook” their bees. This is not the case! As a colony, bees undertake thermoregulation activities to deal with temperatures above and below their optimal range. In the summer, honey bees respond to extreme heat by bearding and fanning. At the end of the day, bees are subtropical insects and are better adapted to high temperatures rather than low ones. Insulating your hives during periods of cold and fluctuating temperatures just helps them better manage the conditions of their hive and conserve resources.
Condensing Considerations
Over winter, clustered colonies produce heat, water vapour, and carbon dioxide. Water can condense on the inside of the inner cover and drip water onto the cluster, diminishing their efforts to stay warm. Many beekeepers and researchers have advised the use of an upper entrance in the winter to help ventilate the hive and reduce the risk of chilling your bees. There has been much discussion surrounding this practice recently, with the concept of running a “condensing hive” over the winter gaining popularity. In a condensing hive, a large amount of upper insulation is installed (minimum R-5 to R-10) and the bees ventilate via one lower entrance.
In the wild, honey bees tend to choose nesting cavities with a single lower entrance. Some have speculated that beekeepers are over-engineering the hive by giving the bees more ventilation than necessary. Proponents of the condensing hive theory claim that a significant amount of heat can be lost through an upper entrance, acting as a source of stress for the colony.
The condensing hive theory asserts that when the bees are clustered, a “heat pool” is created on the ceiling of the hive. A well-insulated hive creates a hotter heat pool than an uninsulated hive. With increased airflow through an upper entrance, a higher proportion of the colony’s heat is lost, the heat pool becomes much smaller and cannot be sustained for as long. Additionally, a water source is needed to dilute honey for consumption during the winter. Bees use the condensation that occurs as a result of water vapour contacting cold walls inside the hive for this purpose.
There is much more research to be done on this topic. As beekeepers, we are far from finished learning about how to best manage our bees over winter. If you’re using NOD’s Bee Cozy Winter Hive Wrap, it’s designed so that neither the wrap nor the top insulation impede the top entrance—so you can choose whatever level of ventilation you prefer for your hives.
Looking to Winter’s End
Remember, there’s no need to rush taking your Bee Cozy Winter Hive Wraps off in the spring! Insulation is crucial for maintaining a steadier temperature within the hive and cluster. Plus, an early spring cold snap could spell disaster for a hive if food stores and insulation are not adequate. We advise removing your Bee Cozy when temperatures are consistently above the cluster point of 10 °C (50 °F), and the possibility of snap freezes has passed.
As spring begins here in the Northern Hemisphere, we wish you a strong start to your beekeeping season!
