The hive climate probably has a major influence on bee health. On the one hand, excessive moisture leads to the growth of pathogenic germs and thus to a direct damage to health. On the other hand, the need for the bees to regulate the climate ties up valuable time and energy. If it gets too hot in the hives in summer, for example, the bees are forced to invest a lot of time and energy in cooling (humidification and ventilation). If the breeding room cools down too much in autumn/spring, the bees have to invest time and energy in heating.
This time is not only lacking for honey production, but also for important tasks such as applying propolis and grooming.
A high humidity additionally damages the bees by the unrestricted reproduction and an increased life expectancy of several parasites. A dry climate, on the other hand, damages the parasites. The larvae of the small hive beetle tend to dry out at a relative humidity of less than 50% (source: University of Florida). A relative humidity below 34% inevitably leads to dehydration (source: Current Zoology).
Relative humidity below 34% also inevitably leads to dehydration of the wax moths larvae. Above this humidity, the survival of the larvae increases with increasing humidity. The wetter it is, the better and faster they develop. The life expectancy of the adult animals also increases with increasing relative humidity (source: Current Biotica).
A humidity of 40%-50% corresponds to the climate in natural tree caves inhabited by honeybees in summer.
The natural behavior of the bees to reduce humidity
In 45 Mio. years of evolution, bees have learned to reduce the humidity in hollow trees very effectively. To do so it needs the geometry and thermal insulation of hollow trees and a lot of wood. In March 2017, we published an article on how bees reduce humidity in bee hives by means of active ventilation.
By several steps of ventilation the moisture generated in the bee nest is brought into its lower areas. There it is ideally absorbed by the surrounding wood by sorption and / or removed by vapor diffusion to the outside. The worst case would be that saturation of the wood has already occurred and the water condenses on the surfaces. The bees generate this way a dry climate in the upper areas.
This behavior of the bees is adjusted to the properties of hollow trees. In modern hives it works only moderately, because of the poor insulation and wide hive geometry. They reduce the humidity in the center of the nest. At the edges of the combs this behavior fails. The moisture already condenses before it can be fanned downwards by the bees.