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Is Moisture Normal…In a Hive?

Posted May 1, 2024

Introduction

Water plays a critical role in honeybee biology and overall health. Honeybees rely on water for various purposes, from maintaining their internal temperature to diluting food sources and supporting the growth of their brood. In regulating the internal temperature of the hive, honeybees use water to cool down the hive by using evaporative cooling techniques. They collect water and spread it across the surface of the hive, allowing it to evaporate and lower the temperature. Water also plays an important role in the growth and development of honeybee larvae. The brood needs a moist environment to thrive, and bees use water to maintain the humidity levels necessary for larval development. Water is also an important component in the production of royal jelly, the nutrient-rich substance fed to queen larvae, further emphasizing the importance of water in honeybee biology.

Water is not only required but is also a bioproduct of honeybee biology. Digestion is one source of water in the form of water vapor. The water vapor comes from metabolizing (digesting) honey resulting in the exhalation of carbon dioxide (CO2) and the release of water as vapor (H2O). Adequate hydration is then crucial for the proper functioning of a honeybee’s physiological processes to maintain their internal water balance, ensuring the optimal functioning of their organs and systems. Water is also essential for the excretion of beeswax scales from their abdomens. This is a vital substance whose primary component is water.

Furthermore, water plays a crucial role in the dilution of nectar and honey. Honeybees collect nectar from flowers and convert it into honey. Water is added to the nectar during this process, reducing its viscosity and making it easier to store and consume. This process also helps regulate the moisture content of the honey, preventing it from crystallizing.

Microclimate

Hives are microclimates with conditions that require careful control to remain at optimum levels of temperature and humidity at all times. Changes and especially quick ones can turn harmful if left unchecked for long periods of time. Honeybees are always regulating the temperature and humidity of the hive with or without intervention from the beekeeper and often because of the beekeeper.

As a rule, honeybees need an optimum temperature of 95⁰F (35⁰C) in the brood area. It may be different in other areas of the hive depending on the area, and the activity of honeybees. Researchers have found an average temperature of 71⁰F (21.67⁰C) in the hive that is immediately above the brood area during winter. Empty areas of the hive that are not in current use, have been found to have temperatures as low as 52⁰F (11.11⁰C) during winter. This temperature gradient is natural in honeybee colonies. It is a result of the honeybees prioritizing keeping the brood warm over warming other areas of the hive. Falls and rises of temperatures below or above the optimum temperature are injurious. Extreme falls and rises can cause temperatures to reach levels where they cause the death of honeybees and brood.

The optimum humidity of the hive is between 50% to 60%. Any drops or rises in humidity below or above the optimum of 60% poses a risk to honeybees, their eggs, honey production and impacts pests and parasite infestations among others. Humidity affects various aspects of the life of honeybees. Firstly, low humidity below 50% causes eggs of honeybees to desiccate. The eggs cannot hatch and may get damaged, thus resulting in a drop of the population of the affected colony. Secondly, a humidity of 60% is best for the evaporation of water from nectar in the hive. When the humidity gets too low, they release water into the hive to raise the humidity level. They may also fan humid air from outside the hive into the hive cavity to increase the humidity of the hive cavity. If the humidity of the cavity gets too high, honeybees fan dry air into the hive. Since air that is cold does not hold water as readily as warm air the bees may also warm the hive to increase humidity and then do the reverse by expelling the warm air from the hive together with the moisture if needed to maintain optimal conditions.

Efficient Thermoregulation

Honeybee colonies behave like ‘superorganisms’ where individuals work together to promote reproduction of the colony. Social cooperation has developed strongly in thermal homeostasis, which guarantees a fast and constant development of the brood and the cooperation of individuals in reaction to environmental variation to achieve thermal constancy of 93-96⁰F (34–36 °C). When environmental temperature changes, heat production is adjusted both by regulation of bee density due to migration activity across the comb and by the degree of endothermy. Overheating of the brood is prevented by cooling with water droplets and increased fanning, which starts already at moderate temperatures where heat production and bee density are still at an increased level. This interlaced change and onset of different thermoregulatory behaviors guarantees a graded adaptation of their individual behaviors to stabilize the temperature of the brood. Thermal homeostasis of the colony is especially important for the brood because larvae and pupae are extremely stenothermic, only capable of living or surviving within a narrow temperature range. A brood nest temperature of 93-96⁰F (34–36 °C) guarantees a high and constant development speed. Accordingly, the accuracy of thermoregulation is high in the presence of brood, and much more variable and generally lower in colonies without brood. It must be kept in mind, however, that the intensity of reactions necessary to compensate for changes in environmental temperature will change with colony strength and properties of its nest insulation.

High Humidity is Critical

Another important factor for brood development is relative humidity (RH) within the colonies. It’s been found that RH is regulated largely by workers and is particularly important for egg hatching and for larvae development. RH below 50% hinders egg hatching in open cells and the optimum RH range at the bottom of the cell for normal hatching is from 90 to 95%. Higher or lower RH significantly reduced the number of normally hatched eggs, and no eggs were able to hatch at 30%. In case of low RH conditions, honeybees show specific behavior such as nectar water evaporation and foraging for water collection to increase RH. During elevated RH, fanning behavior can work well to reduce RH to be within the optimum range. It is worth mentioning that for the rearing of capped larvae, a temperature of 93-96⁰F (34–36 °C) and internal cell RH of 90-96%, with its porous capping, are optimal.

RH is also important in dry and hot conditions as it can attribute or negatively impact the longevity of the honeybee. At temperatures of 93-96⁰F (34–36 °C) workers have been found to survive better at 75% RH, whereas at low RH of 15-50% worker survival was negatively impacted, especially at 15%. Feral and domestic honeybees of Arizona showed high body water loss with decreasing RH, especially at 0% RH and temperatures of 93-96⁰F (34–36 °C). The same trend was recorded with increasing temperatures. This certainly reminds us of the honeybee’s evolutionary origins and preferred tropical conditions they are instinctively trying to recreate especially when brood rearing. A fact that beekeepers should recognize and not fight when artificially stimulating brood in temperate climates or drastically changing their internal environment through excessive inspections. Maybe we are fighting a losing battle and should reconsider the reasons and effects of early spring inspections and feeding as one way in reducing early spring dead outs.

Water, Temperature and Decay

It’s been discovered that tree decay is an important factor affecting cavity temperature, with cavities in live trees warming up and cooling down more slowly than those in dead trees. This is because live wood holds more water than dead wood. Water has a high specific heat capacity, meaning that it absorbs a lot of heat before it gets hot. Most wild colonies occupy cavities in live trees, so most wild colonies experience the moderating effects on nest temperature of being surrounded by heavy, water-laden wood.

Cocoons and Humidity

Honeybees spin a silk cocoon within the capped cell for protection against predators, modifying their local environment, thus facilitating thermoregulation, and influencing water retention. The silk is formed in their labial glands as a helix of four strands which are coiled to form a silk thread. This structure enables water repellent residues (hydrophobic) to be shielded in core positions and polar charged residues such as water molecules to fill non-core positions, thus making the silk readily moisture absorbent (hygroscopic). The silk is ultimately incorporated into the cell walls. As an adult emerges from its cell, the cell is cleaned of debris before the queen lays another egg in it, but the silken cocoon remains. With successive generations, the cocoons therefore accumulate in a cell, eventually replacing the hydrophobic wax and causing the darkening of the comb. The accumulation of cocoons in the thousands of cells used for brood rearing may have significant implications at the colony level. The cocoons could affect nest environment regulation (homeostasis) by buffering humidity fluctuations (storing and releasing) and thus passively influence the regulation of this parameter, as well as temperature in the nest.

Honeybee brood comb containing cocoons absorbs a large amount of water and can release it when humidity decreases. Fanning by workers could ensure the hive atmosphere remains within a humidity range that is favorable for evaporation of nectar and prevents microbial growth, whereas high humidity necessary for brood development is likely to be maintained only where it is important, i.e. within the cell. Hygroscopic cocoons that are incorporated into the cell walls could play an important role in buffering humidity fluctuations and may also influence thermoregulation. This may be the reason why there is better survivorship of brood reared in an older, darker comb with its higher buffering capacity than light comb. Could this also be a reason why honeybees appear to continue to raise brood in old comb and store honey in lighter comb? Maybe we shouldn’t take old comb out.

Water, water everywhere yet not a drop to waste.

One of waters primary roles is regulating the internal temperature of the hive. Honeybees use water to cool down the hive during hot weather by using evaporative cooling techniques. They collect water and spread it across the surface of the hive, allowing it to evaporate and lower the temperature inside. Water also plays a vital role in the growth and development of larvae. The brood needs a moist environment to thrive, and bees use water to maintain the humidity levels necessary for larval development. Moreover, water is an essential component in the production of royal jelly, the nutrient-rich substance fed to queen larvae.

The availability of water also has a direct impact on the overall well-being of bees. Adequate hydration is crucial for the proper functioning of a bee’s physiological processes. Bees need water to maintain their internal water balance, ensuring the optimal functioning of their organs and systems. Water is also essential for the production of beeswax. Beeswax is synthesized by the bees’ bodies, and water is a primary component in its production. Without access to water, bees would struggle to create the intricate structures that house their honey and brood.

Furthermore, water plays a crucial role in the dilution of honey which is critical during winter days when they are unable to break cluster to forage for it. So where do they get that water within the hive? To start with, they seal the interior of the cavity with propolis and wax to make the surface relatively impervious to water. Their bodies give off moisture (water vapor) as part of the process of digesting their food and by breathing. And then they take advantage of the increased relative humidity and resulting condensation. Relative humidity is the percentage of water vapor in air relative to the amount that it could hold if fully saturated at that temperature (the warmer the air, the greater the amount of water than it can hold). Like the effect of causing very low humidity by heating the air in a house during winter, the relative humidity in the warm core of the cluster will be quite low, causing the bees there to be perpetually thirsty. On the other hand, water vapor condenses into liquid water on surfaces that are below the dew point (the temperature that water vapor at a given relative humidity will start to condense). Roughly a non-flying colony consuming a typical third of a pound of honey per day produces roughly a half cup of water vapor per day. How much water are we talking about? It turns out that 40 pounds of honey, when metabolized, produces a total of 26.9 pounds of water, over 3 gallons.

Honeybee eggs require high humidity, a minimum of 55% even to hatch, and do best at 90-95%. Also, the reproductive success of Varroa parasitic mites decreases with increasing humidity. And larvae lose moisture both by respiration and by desiccation owing to the permeability of the larval cuticle. The royal jelly fed to larvae has a high amount of water which may serve to replenish the water lost. In contrast to the high humidity levels within the honeycomb cells containing eggs and larvae, bees fan to reduce the humidity in the brood chamber, maintaining it at 40%-70%. Besides the humidity from the jelly and nectar fed to the larvae, nurse bee respiration and cuticular loss also introduce moisture to the local environment.

Condensation

The air in the heated dome of a tree nest is warmer and contains more moisture than other air in the hive. When the dome’s air begins to cool and circulates downward it touches a cooler surface such as the walls of the nest where condensation forms on that surface. Most hives are milled lumber, with an R-value (insulation value) of 1 or less. Even polystyrene hives have just an R7 value above and at the sides. Honeybees in the wild live inside hollow trees, which may have 3-7-inch-thick walls (insulating value of R3 to R7) and a whole tree’s worth of wood above the colony’s cavity (extensive R value). The tree nest is then well insulated, particularly at its roof. Warm moist air rising above the cluster doesn’t condense on their ceiling but instead forms a vapor plume that rolls outward and condenses on the cooler walls. Some beekeepers see moisture on the inner cover, and the walls, or trickling out the front entrance of hives in winter and feel that something must be wrong. However, moisture in the hive is perfectly natural. The unnatural part of the picture is artificial hive construction, which lack the shape and insulation levels of a hollow tree especially with its greater ceiling insulation. Introducing more insulation into man-made hives can’t hurt, and likely will bring hives a little closer to their natural home in thick-walled tree trunks allowing them to spend their winter in a steady, quiet, dormant state eating less stores. Also, since tree insulation values don’t change in the summer maybe man-made hives should retain their winter insulation helping the honeybees year-around to better manage their temperature and humidity.

Ventilation

It’s always wise to consider our man-made hives in relations to what honeybees prefer in the wild. Their tree nests normally have one lower entrance, thick insulation, propolised walls to reduce the absorption of water vapor by the wood grain, and honey stored in the top comb within the heat dome. For the bees, their expensive fuel is the honey they created and stored above as their brood nest moved downward all summer. If a stream of warm air from the heat dome above the cluster is lost all winter through a chimney effect caused by an upper vent, more honey must be eaten during those months to keep the colony at the same temperature.

Will there be enough to make it to spring? If mite-related viruses are under control, the next biggest threat to overwintering bees is starvation, and anything to help bees conserve “heater fuel” will help them. With high ventilation, carbon dioxide is also flowing out of the hive. Normally, a high concentration of CO2 helps keep the colony in a dormant state. The loss of CO2 allows bees to be too active throughout the winter, with a higher metabolic rate compared to a hive without upper ventilation. This is a second way that ventilation can make the hive consume more energy (honey) than necessary. A third thing that flows out of that upper hole is energy, trapped inside the very moisture that some beekeepers are trying to get rid of. When water vapor floats away through the upper hole, both the water and the energy contained within it are lost. If that water vapor is kept inside the hive, and allowed to condense on the walls, latent heat would be released within the hive. This means that forcing condensation to take place inside the hive releases a great deal of heat energy back to support the colony, instead of venting it off to the environment.

Yes, Moisture is Normal…but maybe not your Hive.

The optimum hive temperature and humidity is easy to maintain for honeybees in their evolutionary home…the tree nest. They use various tactics to ensure that the hive always remains conducive for habitation. Interference by the beekeeper can be helpful or harmful to the efforts of honeybees in controlling man-made hive conditions. Any drastic or sudden changes in temperature and humidity such as during inspections are not good for your honeybees. Honeybees know what they need to do and have genetic and behavioral signals to tell them what to do in their evolutionary hive. Placed in something different causes issues…that the beekeeper feels they need to address…and the honeybee’s natural behaviors and activities are working too hard to fix. Fix the root issue, the hive design (primarily insulation) and leave the rest to their fine-tuned evolutionary behaviors alone.

We have never known what we were doing because we have never known what we were undoing.

We cannot know what we are doing until we know what nature would be doing if we were doing nothing.

~Wendell Berry, “Preserving Wilderness” 1987

Referenced Materials

Robbing Stress

Harbo Assay, Varroa Sensitive Hygiene Testing

Mold, should I be concerned?

STOP PRETENDING.

START BEE-TENDING.

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