Winter colony losses are not uncommon, but most deaths trace back to three primary causes. While the sight of a dead hive in spring is heartbreaking, understanding what actually threatens your bees during winter is the first step toward preventing those losses. These threats—starvation, varroa mites and disease, and moisture—rarely work in isolation. Instead, they compound each other, creating cascading failures that even strong autumn colonies may struggle to survive. In this article, we’ll examine what each of these threats is, why it’s dangerous, and how regional variations affect which threat poses the greatest risk to your colonies.
Threat 1: Starvation
What It Is
Starvation is exactly what it sounds like: colonies running out of honey and pollen stores before spring flowers begin providing fresh nectar and pollen. This might seem straightforward, but starvation has a cruel nuance that surprises many beekeepers. A colony can literally starve to death with abundant honey stores just inches away from the cluster.
Here’s why: during extreme cold, the winter cluster contracts tightly to conserve heat. This tight clustering makes the bees remarkably efficient at surviving frigid temperatures, but it severely limits their mobility. The cluster can move slowly across frames to access nearby honey, but if a prolonged cold snap strikes, bees may find themselves unable to reach stores that are just a short distance away. The cluster cannot break apart to retrieve distant honey without risking individual bees freezing. As a result, a beekeeper might open a dead hive in spring to find frames heavy with honey—but the cluster starved where it sat.
Why It’s Dangerous
Starvation is the most universal winter threat, affecting colonies across all climates and experience levels. Winter bees need continuous access to food not just for nutrition, but for heat generation. The cluster’s warmth depends on bees consuming honey and metabolizing it into energy. Without adequate food, the cluster’s temperature drops, bees become lethargic, and the colony enters a death spiral it cannot escape.
The timing of starvation risk varies by region. Northern colonies face 5-6 months without natural forage, making stored reserves critical. But even southern colonies can starve during unexpected cold snaps or when early spring weather tricks them into ramping up brood production before forage is reliably available. Late winter—typically February through early April—represents the most dangerous period, as stores are depleted and winter bees are nearing the end of their lifespans.
Compounding Effects
Starvation doesn’t just kill directly—it amplifies other threats. Starving bees cannot generate adequate cluster heat, making the colony more vulnerable to cold exposure. Malnourished bees have weakened immune systems, increasing susceptibility to diseases and parasites. When bees struggle with inadequate nutrition, they consume stores inefficiently, creating a feedback loop where stressed bees burn through remaining food even faster. A colony facing starvation pressure simultaneously becomes more vulnerable to varroa damage and moisture problems.
Threat 2: Varroa Mites and Disease
What It Is
Varroa mites represent an insidious threat because the damage occurs long before winter arrives. These parasitic mites feed on developing bee larvae during late summer and early autumn—precisely when colonies are producing the crucial winter bees discussed in Article 2. When varroa mites infest a cell containing a developing winter bee, they compromise the bee’s development, damage its fat bodies, and often transmit viruses.
The result is winter bees that look normal but lack the physiological reserves required to survive months of confinement. Their fat bodies may be inadequate for producing vitellogenin and other essential proteins. The viruses they carry—particularly Deformed Wing Virus and other varroa-associated pathogens—further compromise their already stressed systems. A colony might enter winter with appropriate population size and ample stores, yet still fail because the winter bees themselves are fundamentally compromised.
Why It’s Dangerous
Remember from Article 2 that winter bees must possess extraordinary longevity and specialized physiological features to survive 4-6 months. Varroa-damaged winter bees simply cannot achieve this. Their shortened lifespans mean the colony loses population during the critical late-winter period when the colony needs every bee to maintain cluster integrity and begin spring buildup.
Even if a colony has abundant food stores and proper shelter, unhealthy bees won’t survive to utilize those resources. This makes varroa management during late summer and early fall absolutely critical—not optional. By the time winter arrives, the quality of your winter bees is already determined. A beekeeper who neglects autumn varroa treatment has essentially forfeited the colony’s chance at successful overwintering, regardless of how well they prepare the hive in other ways.
Compounding Effects
Varroa damage creates ripple effects throughout the colony’s winter survival systems. Weakened bees struggle to maintain optimal cluster temperature, forcing the colony to work harder and consume more stores to compensate. Their compromised immune systems make them more susceptible to nosema and other diseases that thrive in the stressed environment of winter confinement. Varroa-damaged bees also struggle with moisture regulation—they cannot efficiently process and remove humidity from the hive, making the colony more vulnerable to condensation problems. When the winter bee population begins declining prematurely due to varroa damage, the remaining healthy bees must work exponentially harder, accelerating their own decline and creating a cascade that can doom even a well-provisioned colony.
Threat 3: Moisture and Condensation
What It Is
Moisture management is perhaps the most misunderstood aspect of winter beekeeping. The winter cluster generates remarkable heat—often maintaining 70-80°F at its core even when outside temperatures plunge below zero. This warm air is also humid, laden with moisture from the bees’ respiration and metabolic processes. As this warm, moist air rises (as warm air naturally does), it encounters the cold inner surfaces of the hive lid and upper boxes.
This temperature difference causes condensation—water vapor transforms back into liquid water, which then drips down onto the cluster below. Cold, wet bees lose their ability to thermoregulate effectively. Their fuzzy bodies, which normally trap insulating air, become matted and waterlogged, conducting heat away from their bodies rather than retaining it. While bees can survive astonishing cold if they remain dry, wet bees can die even in relatively mild temperatures.
Why It’s Dangerous
Moisture is often the silent killer because it’s less obvious than empty frames or visible mite damage. A beekeeper might check stores, treat for varroa, and assume their bees are protected—only to lose colonies to condensation drip. This threat is particularly insidious because beekeepers’ intuitions often work against them. The instinct to “keep bees warm” by sealing up the hive and adding insulation can actually trap moisture inside, creating the exact conditions that kill colonies.
Moisture also promotes mold growth inside the hive and creates favorable conditions for nosema spores and other pathogens. Damp hive conditions stress bees at every level, from individual thermoregulation to colony-wide health. This is why proper ventilation—not maximum insulation—is often the key to successful overwintering, though the specific approach must be tailored to your climate.
Compounding Effects
Moisture problems amplify every other winter threat. Wet bees must consume significantly more honey to generate body heat, accelerating the depletion of stores and increasing starvation risk. The stress of constant dampness weakens bees’ immune systems, making them more susceptible to diseases that might otherwise be manageable. Moisture-stressed colonies often show behavioral changes—unusual restlessness, premature cleansing flights in dangerous weather—that further compromise their survival odds. The condensation issue becomes particularly severe in poorly ventilated hives or those with inappropriate insulation strategies, creating conditions where even strong colonies with good stores cannot survive.
Regional Variations in Primary Threats
While all three threats exist everywhere, regional climate determines which poses the greatest risk. As some examples…
- Northern beekeepers in Minnesota, Maine, or similar climates face starvation as their primary enemy. Winters lasting 5-6 months require massive honey stores—often 80-100 pounds or more. Late cold snaps in March and April are particularly treacherous, striking when stores are at their lowest and winter bees are nearing the end of their lifespans. Northern beekeepers must also balance insulation needs (protecting against extreme cold) with moisture management, a challenging equilibrium that changes throughout the winter.
- Southern beekeepers in Georgia, Texas, or similar regions face different challenges. Varroa pressure continues later into fall as warmer temperatures keep mites breeding. Warm winter spells disrupt the cluster, causing bees to break cluster and increase activity, consuming stores faster than necessary. While shorter winters might seem easier, they present unique management challenges—colonies may attempt brood-rearing during warm spells, depleting stores and protein reserves that won’t be replenished until spring forage arrives.
- Mountain and high-elevation beekeepers face perhaps the most challenging conditions: extreme temperature swings and wind exposure. A sunny day might reach 50°F, followed by nighttime temperatures of -10°F. These rapid swings stress colonies tremendously, as bees respond to warm spells with activity that depletes stores, then must rapidly re-cluster when temperatures crash. Wind compounds cold exposure, pulling heat away from hives and making it harder for clusters to maintain temperature. Snow and ice create moisture challenges as melting and refreezing cycles introduce water into hive structures.
Looking Ahead
These three threats—starvation, varroa and disease, moisture—sound daunting, but they are manageable. With proper preparation and appropriate winter management strategies, beekeepers can dramatically improve their colonies’ survival rates. Understanding what threatens your bees is the essential foundation for knowing how to protect them.
In the following articles, we’ll move from understanding to action. You’ll learn exactly how to prepare your hives to address each of these threats, with specific strategies tailored to your regional climate and your colonies’ individual needs. Winter is challenging for bees, but armed with knowledge and practical preparation, you can help your colonies emerge strong and healthy when spring finally arrives.
