by Tony Jadczak, Maine Apiarist
Unlike the majority of northern insects, honey bees cannot survive freezing and do not hibernate. In fact, the reason honey bees gather and store surplus honey is for con- sumption during the winter months when flowers are absent and temperatures are too cold for flight. The bees store honey above and around their cluster and move up into the honey reserves as winter progresses.
It is common knowledge that honey bee colonies can winter successfully in cold climates without wrapping or packing if the basic essentials regarding colony strength, health, ventilation and food stores are met. For example, in Nova Scotia, single story hives can winter on a minimum of 40 lbs of honey, while in Québec, a minimum of 70 lbs of honey properly situated in double brood chamber hives can successfully winter.
During the darkest days of winter when temperatures are often the coldest, northern hives appear lifeless. However, within the hive approximately 25 – 30 thousand winter bees (6 – 8 lbs) that differ physiologically from summer bees are clustered in an elliptical sphere, consuming honey stores and shivering to generate heat. The winter bees are reared in fall and have an abundance of fat bodies and enlarged hypopharyngeal glands due to the cessation of brood pro- duction and associated gorging on pollen and honey prior to winter.
This added nutrition coupled with lack of brood production results in a long-lived bee. Winter mortality and an increased incidence of nosema is common in years with poor fall nutrition such as the north- east experienced during 2007/2008.
Numerous studies by honey bee researchers such as Corkins, Farrar, Furgala, Owens and Moeller have defined the parameters of cluster formation and the efficacy of honey con- sumption and thermoregulation of colonies during winter. Farrar used 188 thermocouples situated throughout the hive to record tem- peratures in single- and double-walled hives and also did experiments with exposed hives that had only screens for walls.Bees begin to form a loose cluster when the temperature within the hive reaches 57.2°F and at 42.8°F all of the bees within the hive become involved and form an “insulating shell” of 1 – 3 inches thick. When tempera- tures within the hive become cooler, the cluster contracts, and visa versa as tempera- tures warm up. Research also demonstrated that the temperature of the cluster surface is maintained at approximately 44°F (43 – 46°F), regardless of how cold it is outside of the hive. The outer cluster temperature varied somewhat under humid conditions at a range between 48 – 52°F. Research also proves that bees do not heat the unoccupied area of the hive and the temperature of frames of honey and comb outside of the cluster are near the ambient. It has also been determined that the optimal temperature for honey consumption is 45°F and that hives consume more honey in warm winters, when temperatures fluctuate and when disturbed by beekeepers, mice and shrews. In general, colonies consume about 1 – 3 lbs of honey per month during October – January and honey consumption increases with the onset of brood rearing to about a 1?2 lb per day by April. When bees consume honey, the digestion process (oxidation of sugar) results in approximately 1 gallon of water vapor produced per 10 lbs of honey, a production of carbon dioxide and uric acid waste that accumulates in the bees’ rectum. When the level of carbon dioxide reaches approximately 10%, the bees fan to create a current for air exchange within the hive.
There are competing theories regarding the behavior of the winter cluster. The most popular view is that the bees in the center of the cluster shell are more active, at a lower density and consume honey and shiver to generate heat. The bees in the shell are thought to be denser, less active and slowly rotate or exchange position with those near the center so no individual bee becomes chilled at the periphery of the cluster. It is commonly thought that the bees in the warmer portion of the cluster pass honey to the bees at the periphery of the cluster as long as the cluster has contact with its food reserves and that the heat is conducted (through insulation) outward to the insulating shell. This theory has been challenged due to the physics of “conduc- tive insulation.” Mobus has challenged the theory, citing work that indicates that the bees at the warm center of the cluster used very little honey and therefore produced little heat. He states that the bees were essentially at “idle,” but were evaporating more water than those occupying the outer shell. It was found that the bees in the outer shell produced more water and carbon dioxide and therefore were the most active converters of nearby honey stores. Mobus contends that the bees within the cluster will migrate toward the periphery to get a “metabolic drink” and the outer shell bees move inward to “dry out.” He states that the behavior is a selfish, survival-oriented exchange of bees between layers which is driven by thirst or water surplus rather than an altruistic behavior of letting sister bees warm their feet. Physics and behavior aside, it is known that the clustered bees exchange position during the winter months.
It is common for bees to occasionally fly during winter and beekeepers are often concerned when they see bees scattered in the snow throughout the apiary, often at a distance from the hives. Conventional thinking is that these are the older bees and/ or those afflicted with parasitic mites, virus or nosema. Bees will take brief cleansing flights in order to defecate at temperatures of 44°F or more, evidenced by yellow spots in the snow a short distance from the hive. Over the years I have collected and exam- ined bees found frozen in the snow a good distance from the hives for parasitic mites and nosema, only to find the vast majority negative for these common maladies. Con- versely, bees collected and examined directly in front of hives were more likely to be afflicted with nosema and/or tracheal mite.
Recently, Fred Wardwell, Searsmont, of the Tri-County Beekeepers Association, sent me an excerpt of the book Winter World by Bern Heinrich. Heinrich examined other possibilities than “cleansing” for bee flight during winter when temperatures were
33 – 36°F, where bees rapidly cool, fall to the snow and die.
Heinrich theorizes that perhaps the ultimate reason for some of the so-called cleansing flights could be something dif- ferent. Heinrich asks, “Could the flights be scout bees searching for flowers to get food, or water to drink?” Paraphrasing Heinrich: The bee cannot know if or when the red maple, willows and poplar trees in sur- rounding bogs will bloom. The colony can’t afford to miss early spring nutrition…but it can afford to lose some workers to “buy information.” There is a premium for early swarms to leave a colony and the only way for the bees to get information on when the first blooms are available is to fly out and search. A few hundred or a few thousand worker bee deaths may be a small price to pay for being at the first bloom. The honey bee is a superorganism and its success is measured by the reproductive output of one queen. Perhaps the scouting attempt during winter can be likened to the altruistic behavior of the worker bees that die as a result of stinging an intruder such as a bear or skunk in order to protect the hive. A most interesting hypothesis!
For now, the best winter management a beekeeper can do for the health of his/her bees is nothing. Do not disturb them until February or March—and when the time arrives, have a purpose, be quick and do only what is necessary. Enjoy the holidays and Happy 2010!
Tony Jadczak, State Apiarist
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