Varroa is an opportunistic parasite

Symptoms which are often attributed to varroa are in fact the consequence of anaerobic conditions being created and excessive growth of bacteria. However, these processes are not actually visible, but their consequences are.

Certain substances are produced in anaerobic conditions and by certain bacteria; these substances have considerable influence on the behavior of bees, bee colonies and the mites. For example, this leads to the disappearance of bees. The increase in the numbers of microorganisms goes hand in hand with the increase in the numbers of varroa mites. Varroa in itself is not the reason why bees colonies become weakened, suffer from winter mortality, diminishing populations in the summer or why bee colonies ‘disappear’. The underlying processes are the true cause. We endeavor to explain this in more detail here.

Explosive growth of varroa

The explosive growth of varroa, as is often observed, is the consequence of microbial growth. Microorganisms are a source of nutrition for the mites; in other words they benefit from the mites. Only when the food supply for the varroa mite is threatened do the mites feed on the bees with hemolymph. Accordingly, Varroa is a facultative parasite (opportunistic parasite). This means that the mites only parasitise the bees if there is no other means of survival; in other words if there is insufficient food for the mites. The mites need certain bacteria to successfully parasitise the bees. For a further explanation of this process see the tick model.


A bee system is not only a community of bees, it is primarily a community of microorganisms. Just as in humans where the number of intestinal bacteria by far exceeds the number of cells in the body, the same applies to bees. There are at least four groups of microbiological systems which are significant in bees and bee colonies. These are:

  • Microorganisms that play a role in the conversion of food brought into the hive into bee bread (mainly pollen)
  • Microorganisms that are involved in the formation of honey from the nectar brought in
  • Microorganisms that play a role in the digestion and absorption of food in the bees’ intestines
  • Microorganisms that are present on the bees, for example on the exoskeleton

Microorganisms on the bees

The bees are always host to numerous microorganisms. Explosive growth of bacteria can have a dramatic impact on the bees. These non-pathogenic bacteria secrete substances which cause the tracheae to become clogged.

Consequences of clogged tracheae

If the tracheae become clogged, the exchange of gasses ceases. Clogged tracheae hamper the bees ability to absorb oxygen and discharge CO2. An anaerobic situation quickly arises. If this anaerobic situation lasts too long, then considerable changes occur in the bees.


In general, the presence of such microorganisms on bees is referred to as a biofilm. The bacteria in the biofilm are relatively protected from external influences, because they are covered by a layer. A biofilm usually consists of multiple types of bacteria which keep each other in equilibrium. A biofilm is normally stable and is difficult to remove or degrade.

Biofilm degradation

Biofilm degradation may take place under the influence of chemical substances such as strong acids, metals and chelates, or by means of mechanical forces (rubbing, for example). The varroa mite also bears such a biofilm. However, this has little or no influence on the mites respiratory system. This is because mites and acaridae have a totally different respiratory system than bees.

Maintaining control

Under normal circumstances bees are not affected by the microorganisms that colonize their exoskeleton. Bees keep their bodies clean through grooming. The microorganisms on the exoskeleton are also a source of food for bees. It cannot be ruled out that these microorganisms also influence the intestinal flora once ingested.

The biofilm, present on the bees, blocks the tracheae. If there are no varroa, the bees have to continually remove this biofilm by grooming or by excreting certain substances. If varroa are present, the mites assist the bees in this task. So, to a certain extent, varroa mites do have a useful function.

Consequences of an anaerobic situation

The first significant consequence of an anaerobic situation is that the energy production of the bees drops considerably. An important characteristic of an anaerobic situation is that there is a lack of oxygen. A lack of oxygen usually affects the brain first. The brain needs energy to function properly. If energy production in the brain is insufficient, this causes neurological problems immediately. In bees, this is visible in the form of behavioral changes.

Release of Mn2+

Another important consequence of an anaerobic situation is that manganese is released in the form of Mn2+. The consequences of this are as follows:

  • Mn2+ encourages reproduction
    A consequence of the release of Mn2+ is that reproduction increases. This affects the mites as well as the bees, and means that both mite and bee populations increase. Generally speaking this pattern commences in July, while the bee colony should be gradually decreasing in population in preparation for the winter. In fact, the system is sent off in the wrong direction.
  • Mn2+ causes substances to develop which influence the behavior of bees
    The release of Mn2+ causes bees to leave the hive. Mn2+ stimulates the bees to retrieve nectar rather than pollen. The bees escape the anaerobic situation by leaving the hive.
  • Mn2+ results in iron being displaced in ferrous enzymes
    This affects many important functions and some may even cease to function at all, which then opens the gate to all manner of disease and is often fatal to the bee colony.

Explanation of anaerobic situations in the bee system

Anaerobic situations in bees and bees colonies can arise in different ways. Beekeepers can recognize an anaerobic situation by the distinctive smell in the hive. If an anaerobic situation arises in the bees, as explained above, this results in a decreased activity of the bees due to diminished energy production. Varroa mites are not affected so severely. At this point in an anaerobic situation, the varroa mites have a competitive advantage


In anaerobic situations:

* varroa has a competitive advantage

* reproduction increases

* bees leave the hive

* conditions for pathogens are favorable

Should beekeepers attempt to combat varroa?

It only makes sense to combat varroa if the resources used influence the processes described in this article. If strong organic acids such as formic acid and oxalic acid are used against varroa, this also weakens the bees. This is because these substances extract iron (and other minerals) from the bees, which eventually leaves the bees with insufficient minerals and/or iron to function properly.

That ‘substances to combat varroa’ have a modest effect on problems such as winter mortality has more to do with the fact that these substances affect other aspects of the hive than simply ‘combating varroa’. ‘Substances to combat varroa’ do not do anything to prevent an anaerobic situation from occurring. That is the primary reason that these substances only have a limited influence on bee mortality.


The ferrous product Ferro-Bee® prevents adverse consequences of Mn2+ release from occurring. Ferro-Bee® has multiple effects that cannot always be distinguished from each other. Order Ferro-Bee®here.