Of course, this is a simplification. At some point “warm” becomes “hot” and “hot” becomes “too hot”. In our own human-centered world, we have the advantage of air conditioning and many ways to maintain our own comfort.
But what about our bees? How do they cope with increasing temperatures, especially within the confines of a hive?
It’s a complex story. Our bees have their own tactics and there are also ways in which we can help them achieve a manageable temperature.
The Dangers of Hot Weather
A hive that is well-regulated by bees has a temperature between 91 and 97 F (33 – 36 C), to support the raising of brood. While adult bees can withstand much higher temperatures, a healthy colony requires the ongoing creation of new bees. Brood requires a lower “working temperature range” and keeping brood within these boundaries can be one of the most challenging of tasks for worker bees.
Interestingly, a more genetically diverse colony will maintain more stable brood temperature than a colony a more uniform colony. The theory here is that the genetic lines evident in the makeup of the colony will each have their own response threshold. This, in turn, means a “fine-tuned” response as brood temperature changes.
One might consider the emergence of a bee from a cell to be the measure of how successful brood temperature has been maintained. But the important results are seen in adult bees.
First, even small deviations from optimal brood temperature can create adult bees that are more vulnerable to the impact of pesticides. Secondly, the complex and important process of assigning tasks to adult bees is affected by brood temperature.
So, it is vital that our bees have the ways and means to regulate brood temperature carefully. Thankfully, they have a number of ways to achieve this.
Bee Cooling Tactics
Fanning
Perhaps the most obvious behavior we observe in our bees to stay cool is fanning at the entrances of the hive. Consistent with many bee behaviors, it’s a team effort.
For starters, this is one (somewhat rare) aspect of life within the hive itself where drones play an important role. Contrary to the common impression that drones have one thing in mind – mating. And, of course, their role is essential there, especially in terms of increasing genetic diversity, as they visit a Drone Congregation Area. But drones also recognize the importance of a well-ventilated hive and will assist in the fanning of the hive, alongside workers.
Fanning of the hive is sometimes confused with the spread of the Nasonov pheromone, which helps other bees with their orientation. In this situation, their rear ends are tilted upwards. By comparison, when bees are lined up to fan the hive for ventilation purposes, their rear ends are generally held lower and they are closer to the hive entrance.
Easing Congestion Through Bearding
Beyond the mechanical benefits of fanning air through the hive, another factor directly impacting the temperature is the pure number of bees in the hive. When temperatures rise, bees will first spread out within the hive, to use a greater space and reduce bee density. This is effectively the opposite of the clustering behavior used to regulate against dropping temperatures.
When temperatures rise still further, the number of bees in the hive may simply be too great. Consider brood a “layer” that must be maintained at an appropriate temperature. When the number of bees increases this layer is covered by more bees. This reduces the effect of the fanning activity and the overall temperature of brood can become dangerously high.
The solution to this is to get bees out of the way! This is often seen as “bearding”, on the outside the hive. Bees come out of the hive, instead of congesting the restricted space inside. This is an important behavior for the beekeeper to observe, with the outside of the hive often covered with many bees.
Bearding can be a worrying event for the new or uninformed beekeeper. While the activity is indeed a response to a potentially difficult situation – depending on how high the temperature rises – it is also a perfectly normal and common behavior in the hot days of summer. New beekeepers often confuse bearding with the potential of swarming, but there are some differences.
- Bearding is more likely to occur in the middle or end of summer, as temperatures are at their highest.
- Bearding can continue till temperatures start to fall in the evening.
- Bees participating in bearding will simply want to stay away from the congestion in the hive until the situation has improved.
Cooling With Evaporation
While we tend to consider fanning as the most obvious sign of bees working to regulate hive temperature, there’s another very important element of this effort – water.
Availability of water and its intelligent within the hive is essential. Dedicated worker bees will depart the hive with the specific intent to forage water, not pollen or nectar. They will settle at a water source and spend time sucking water through their proboscis.
On returning to the hive, the water forager will pass off the water to a worker. That worker will smear droplets across cells and this will then be fanned. The resultant evaporation creates a cooling effect.
The water foragers will assess the dynamic need for water in the hive on an ongoing basis. based on the readiness and speed with which collecting workers are able to accept water.
As an aside, nurse bees also have a significant water requirement, in terms of their need to produce food for larvae.
How Beekeepers Can Help
There are many ways in which beekeepers can help our bees, in their quest for acceptable conditions within the hive. The main principles come down to helping bees ventilate the hive (such as having entrances at both the bottom and top of the hive, for example) and ensuring adequate access to water.
It’s Not All Bad
Despite the challenges of high temperatures and the efforts to which bees will go to regulate within reasonable bounds, there is some evidence of benefits from higher temperatures. Some beekeepers have expressed interest in the concept of “thermotherapy”, based on the fact that raising the temperature for short periods of time does not seem to be problematic for bees or brood – but can kill Varroa mites!
Although somewhat controversial and not universally accepted as a viable approach, the ThermoSolar Hive looks to take advantage of Varroa’s inability to survive high temperatures. By raising the temperature to 40 degrees C for 150 minutes, the makers of the ThermoSolar Hive claim it can completely eradicate mites in capped cells. Such approaches are, at least, an interesting area of research.
