In many parts of the world, temperatures range from freezing cold to scorching hot throughout the year. In some areas, honeybees can be subjected to these temperatures on the same day. This has forced them to develop incredible hive temperature regulation methods to help control the internal temperature.
The internal temperature of a beehive plays a vital role in the overall health of the colony. The right temperature means the colony can raise the brood under stable conditions, as well as survive harsh temperatures in both winter and summer. If the temperature inside the hive becomes too hot or too cold, the survival of the colony is threatened.
How Hot Is It Inside A Beehive?
The most important part of a beehive when it comes to temperature control is the area in which the brood is kept. The brood needs temperatures to be between 34°-36°C (93°-97°F). Studies suggest that a temperature outside this range can have negative effects on the health of emerging adult bees, and result in a reduced life expectancy.
For that reason, the brood area is kept inside these temperatures, while the temperatures in other parts of the hive fluctuate over a much larger range, and can reach temperatures similar to those outside the hive.
Optimal Beehive Temperature Is Needed For A Healthy Colony
Brood health is of great importance to a colony. If they don’t have healthy brood, they can’t raise healthy adults to take care of the hive, gather food, and protect the colony from predators.
Temperatures outside of the critical range of 34°-36°C (93°-97°F) can lead to birth defects. If a bee grows from larvae to adult when the hive is at a temperature of 33°C, for instance, they are significantly more susceptible to pesticides. The temperature outside the optimal range can also affect the wing development, learning ability, and even the color of emerging adult honeybees.
In the colder months, it becomes more difficult to maintain the necessary hive temperature, so there is little to no brood rearing. Instead, bees focus their energy and resources on surviving the cold weather. Typically a queen will stop laying eggs in the lead-up to winter, then start again just before spring.
How Bees Regulate Hive Temperature When It’s Cold
Because beehive temperature is so important, honeybees have developed many effective techniques for regulating temperature. In winter, these include:
Contracting Their Flight Muscles To Generate Heat
Honeybees can increase their body temperature by contracting the muscles in their thorax (the middle part of a bee’s body, where the wings are located). By contracting these muscles, bees can raise their own temperature and use this warmth to heat up the hive.
This requires a significant amount of energy, which bees get from eating honey. This means that bees consume a lot of honey when it’s cold – one of the reasons why it’s so important as a beekeeper to leave your hive enough honey during winter.
A common way in which bees use this technique (contracting the muscles on their thorax) is to maintain the temperature of the brood so the colony can raise healthy bees.
Worker bees press their thorax down onto capped cells that contain pupae in order to keep them warm. They also occupy empty cells throughout the brood area, where they insert themselves head first and transfer heat into the adjacent cells containing pupae.
Forming The ‘Winter Cluster’
One of the main ways in which bees are able to regulate the internal temperature of the hive is by forming clusters. In winter, bees cluster together to reduce the surface over which temperature can be lost.
The winter cluster has two layers. The first is an outer circle, where bees stand side-by-side with their heads facing inwards. The second is the inner layer, where bees are able to move about freely.
Bees in the center of the cluster use their thoracic muscles to create heat. Meanwhile, those in the outer shell form a barrier as insulation, to help maintain the temperature.
Bees will take turns, moving from the outer layer to the inner, then back again. The cluster will break occasionally for bees to feed on honey.
In the winter months when there is no brood, the temperature inside the center of the cluster is typically maintained at around 20°C (68°F). Levels can fluctuate significantly, with temperatures being recorded as low as 13°C (55°F).
While bees are able to maintain a warmer temperature, it would require them to consume a substantially greater amount of honey. They instead choose to conserve food and energy levels for the end of winter when new eggs are laid by the queen.
Site Selection
Because honeybees need a nest site that’s protected from extreme weather, swarms choose their new nest site with hive temperature in mind. That’s why they often choose a hollow log or tree because it provides shelter from the weather.
After finding their new hive, they’ll seal any unnecessary holes using propolis. During winter in parts of the world that get especially cold, bees have even been known to use the same technique to reduce the size of the hive entrance. Humans have adapted this technique into man-made entrance reducers.
Careful Design Of Their Hive
Even the inside of the hive helps bees to control the temperature. Honeycomb is not only used by bees to store food and raise the brood – the layers of comb create barriers against the cold, and bees are able to contract or spread their cluster in the spaces between each sheet of comb.
This is why, in tropical climates where it’s more difficult to keep the temperature low, bees build exposed nests that allow for greater ventilation through the hive.
How Bees Regulate Hive Temperature When It’s Hot
Heat can also be very dangerous for bees. They have developed numerous techniques to help regulate beehive temperature when the weather becomes too hot:
Fanning Air Through The Hive
Fanning by worker bees creates cooling air currents and helps to keep the hive at a desirable temperature. Fanning generally begins when the internal hive temperature becomes too high.
Worker bees face the same direction and fan their wings to help airflow throughout the hive to prevent the brood from overheating. Other worker bees gather at the entrance of the hive and fan inwards.
Evaporative Cooling
When fanning alone doesn’t sufficiently cool the hive, bees use a method that is similar to evaporative cooling.
They spread water on the capped and uncapped cells, and place hanging water droplets throughout the hive. Worker bees then fan their wings to evaporate the water and circulate the cool air around the hive.
Some bees also use their proboscis (tongue) to spread drops of water into a thin layer that can evaporate quickly – a behavior known as ‘tongue-lashing’.
Bearding
When the internal temperature becomes too hot, bees leave the hive and cluster together outside. This behavior is called bearding.
The purpose of bearding is to temporarily reduce the number of bees inside the hive, allowing for better ventilation to cool down the temperature. Bees often beard during summer when temperatures reach extreme highs.
Interestingly, many beekeepers also note their bees bearding in the cool weather and rain, which shows that a low external temperature doesn’t necessarily mean the same for the temperature inside the hive.
Should You Monitor Your Beehive’s Temperature?
Because the internal temperature of your beehive is important for the health of your colony, you may want to monitor it over time.
This is not something I generally do, as I live in a moderate climate where the weather doesn’t reach extreme temperatures on a consistent basis.
Besides taking care to choose the perfect location for my beehive and making sure there is enough water nearby, I generally leave the bees to regulate the temperature of their hive on their own.
Temperature control is something bees are experts at, after all – trying to alter the temperature of a beehive with artificial measures might simply make their job more difficult.
However, if you live in a climate that sees more extreme temperatures – such as snow – then you may want to monitor the temperature of the hive using something like an instant-read thermometer. This can give you an indication of your hive’s health without having to open it up for an inspection.
Beehive Humidity Is Also Important For The Health of The Colony
Like temperature, relative humidity is very important inside a beehive. Humidity that is either too high or too low can have negative effects on the health of the brood. This can both decrease the number of eggs that hatch and also cause health problems in emerging adult bees.
Humidity levels between 90-95% are optimal for the brood area. In other areas of the hive, though, humidity needs to be kept at lower levels, especially in parts of the hive where honey is stored.
Bees make honey by collecting nectar and mixing it with an enzyme called invertase. They then fan their wings until the moisture content is between 14-18%. Once the moisture content reaches this level, the honey is considered ripe and stored inside cells in the hive’s honeycomb.
If the humidity becomes too high, it makes it difficult for bees to turn nectar into honey, no matter how hard they beat their wings. This can be disastrous for bees as they need a lot of honey to survive the winter.
Conclusion
The internal temperature of a beehive is very important for the health of a colony. This is especially true in the area the brood is kept, which must be between 34°-36°C (93°-97°F). Otherwise, the brood is at risk of dying or having health problems when adult bees emerge. Other parts of the hive fluctuate outside of this range.
Bees are highly effective at regulating the temperature inside the hive both during hot and cold weather. Some of these methods include expanding and contracting their cluster, using their flight muscles to generate heat, fanning their wings to create airflow, and evaporative cooling to reduce internal temperature.
