Up to now, the problems with bee colonies have been mainly attributed to varroa. Also with regard to winter mortality, the relationship between varroa and winter mortality is often emphasized. Because of the biased attention to varroa, the microbial and physical processes that take place in the hives and colonies have not been taken into account. We consider this a very serious shortcoming of all the research into bee mortality and problems with bee colonies in general.

There is always an advance trigger to disease, disappearance and death. In our opinion, the presence of varroa mites is mainly due to excessive bacterial growth. The varroa mites diet consists primarily of microorganisms. In other words, if there are many bacteria, then there will be large numbers of mites.* Varroa mites can better be considered as a type of cleaner, a cohabiting organism (commensal) than as a predator, a parasite or a disease. It is only when the food supply for the mites becomes exhausted that they begin to cause a problem for the bees. The small hive beetle, which beekeepers have been ‘warned about’ since the beginning of 2015, can also be considered as a commensal.

* In this publication the following remark supports our view: Varroa have relatively low reproductive rates, so populations should not increase rapidly, but often they do. Other factors might contribute to the growth of varroa populations.

Bee health

When the term bee health is used, it implicitly assumes that there is something wrong with the bees, or that they are suffering from diseases. Bee health a vague and undefined concept. It would be better to refer to the condition of the colonies (strong or weak), or even the condition of the queens.

It is questionable as to whether winter mortality actually has anything to do with the ‘health’ of individual bees. We will explore this idea in the following paragraphs that explain anaerobic conditions.

Anaerobic conditions

As far as we know, in the scientific research conducted thus far, no attention has been paid to the emergence of conditions with little oxygen and the effect of this on the bees and bee colonies. If this has been mentioned, then it was not considered significant and so it received no attention. This is possibly due to the prevailing interest for and research into varroa mites with the corresponding ‘global consensus’ in the scientific community.

In our view, many of the problems with bee colonies can be fully explained by the occurrence of anaerobic situations. Here, we will explain the anaerobic processes that occur in bee colonies to you as beekeeper. This is one of the results of our research into the processes that occur in bee colonies and the possible operational mechanisms of Ferro-Bee®.

Development of anaerobic conditions

The likelihood of anaerobic conditions (shortage of oxygen) occurring is the greatest when the bees are very close together. This can happen due to CO2 production. From the literature it also transpires that even with sufficient air exchange with the outside environment, concentrations of CO2 in the hive can become very high (up to 8%).

If the concentration of CO2 is high, oxygen is displaced. In humid weather, the CO2 concentration is more likely to rise. And it is under these humid circumstances that the bees remain in the hive for a relatively long time. The shortage of oxygen may then continue for too long, and so good ventilation is even more important. This doesn't only mean ventilation from outside to inside and from inside to outside the hive, it also means good ventilation within the hive. The bees themselves must ensure for sufficient internal ventilation, and so the activity of the bees must be sufficient to guarantee that this actually happens.

Danger of anaerobic conditions

An anaerobic situation can occur in the hive as well as in the bees themselves. The main concern about anaerobic conditions is that in such circumstances the energy production is at a much lower level than when there is sufficient oxygen (up to 90% lower). For example, this may mean that bees that leave the hive cannot fly far or that they quickly become exhausted and then fall. In itself, a short anaerobic situation is not serious, the bees generally recover quickly. But there are other dangers of anaerobic conditions which are much more severe.

Bees and anaerobic conditions

Anaerobic conditions in the bees can occur if the tracheae become blocked, for example by bacteria. Then insufficient oxygen can make its way from the hive into the inner parts of the bees. The hygienic behavior of bees which is often mentioned also serves to clean the exoskeleton through which the tracheae (small tubes, also known as spiracles) pass, and so will keep them open.

Mites and anaerobic conditions

When considering the influence of anaerobic situations, it's important to know that the respiratory system of the mites differs from that of the bees. While the exchange of gasses in bees takes place via the tracheae, in the mites, this happens in a kind of cavity. Tracheae easily become clogged, for example due to excessive bacterial growth (and possibly by tracheae mites). Bees are therefore more likely to suffer anaerobic conditions than mites.

Bacteria and anaerobic conditions

One of the consequences of anaerobic conditions is that other bacteria start to multiply. Such changes in the microbiological composition are rapid; depending on the temperature this can occur in as little as 1 or 2 days and, consequently, can affect the availability of certain nutrients.

The winter cluster and anaerobic conditions

Bees huddle very close together in a winter cluster. This hinders the flow of air and increases the likelihood of an anaerobic situation occurring within the winter cluster. This can have a negative influence on the queens in particular.

It is known that the density of bees in the winter cluster depends on the temperature. If the temperature is higher, the bees are a little further apart from each other in the winter cluster. The activity and mobility of the bees is then greater, and therefore there is more air circulation, also within winter cluster. Under warmer conditions, there is less likelihood of an anaerobic situation arising in the winter cluster. And this, by the way, is the primary explanation for the low winter mortality in the 2015/2016 season. Temperatures were in fact fairly high throughout the winter.

We think that the occurrence of temporary anaerobic situations is also useful, because this causes more neurotransmitters to be generated, which in turn affects the activity level of the bees, so that they can reach the food.

Swarms and anaerobic conditions

Bees usually swarm when the number of bees has increased considerably following high and rapid reproduction. With many bees in the hive, the density increases and with this, the likelihood of an anaerobic situation. The individual bees within the swarm cluster start to move from inside to outside and vice versa. This causes increasing numbers of bees to be in an anaerobic situation for a short or longer period of time. In turn, this causes a kind of agitation following the generation of neurotransmitters, which, at a certain point, apparently results in the departure of the bees.

Brood diseases and anaerobic conditions

The microorganisms that play a role in brood diseases are, without exception, types that grow in anaerobic situations. Because the brood cells are closed off with a cap of wax, the chances are that anaerobic situations occur in the brood cells. This may occur, for instance, if the cap is not sufficiently permeable. This may be related to the structure and/or composition of the components.

Bee hives and anaerobic conditions

It is very conceivable that the type of hive also influences the incidence of anaerobic conditions and their duration. Many hives were designed long ago, and it could be that at the time insufficient consideration was given to the occurrence anaerobic conditions. By combining beekeepers' practical experiences with modern techniques, there are certainly opportunities for optimizing the design and layout of beehives. From our discussions with beekeepers, it transpires there are advantages to be gained by making the openings larger, either temporarily or permanently.


One of the effects of Ferro-Bee® often reported by beekeepers is that the bees are more active. By administering Ferro-Bee® at times when there is an increased likelihood of an anaerobic situation occurring, for example in humid weather, the bees become more active and such undesirable anaerobic situations will be prevented.

© April 2016, Science in Water B.V. / Ferro-Bee®

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