Nosema Disease

Bees at Hive Entrance

Bee health is obviously an extremely important issue for beekeepers. To that end, those who are new to the hobby will need to be aware of the different diseases and pests that can affect the honeybee. Some of these issues are more serious than others, with some affecting honey production and others causing the destruction of the entire colony.

If you are a new beekeeper, take some time to read my series of articles on the various diseases and pests that could affect your hive. In this particular piece, I will focus on Nosema disease.

What is Nosema Disease?

Nosema disease – or nosemosis as it is also known – is a microsporidian classified as a fungus that affects the honeybee. There are two types of nosema microsporidian: Nosema apis and Nosema ceranae; both are tiny spores that attack the honeybee’s gut.

Indeed, Nosema disease is the most widespread disease affecting the honeybee; it is also one of the biggest threats to bees throughout the world.

How Does Nosema Disease Affect the Honeybee?

As mentioned above, the tiny spores can affect the gut of the honeybee. Nosema apis originated in the European honeybee while Nosema ceranae is thought to have originated in the Asian honeybee. By far though, Nosema ceranae is the more serious threat to the bee as it attacks more of the cells in the gut. Therefore, it can kill bees much faster than Nosema apis does.   

Nosema spores enter the honeybee’s body through the mouth. To give you an idea of spore size, around 300 of them could fit on a pinhead. Just one spore is enough to cause infection in a bee, but a bee will typically ingest between twenty and ninety of these spores.

Once the spores have entered the bee, they germinate rapidly in the gut. Upon germination, they become active in the epithelial cells of the midgut. This is where it quickly multiplies, forming new spores. These spores will then pass to other tissues in the bee or will be excreted into the hive. If these spores contaminate food within the hive, other bees will become affected and the cycle continues. Unfortunately, the spores can remain viable for a number of months in spots of dried excreta within the hive.

Over the winter, it is likely that combs will become soiled with excreta from the infected bees. When other bees within the hive attempt to clean the combs in preparation for expansion in the spring, they too will become infected.

Bees affected by nosema disease are unable to absorb the nutrients they need. This often leads to them ingesting more food and using the protein to repair their internal body cells instead of using it to feed the larvae.

Infected nurse bees will be unable to produce royal jelly, which is usually fed to the brood. In an infected colony, a large number of eggs laid by the queen will not produce mature larvae. Infected queens often stop laying eggs and will die within weeks.

What are the Symptoms of Nosema Disease?

Alarmingly, bees affected with nosema disease often show no symptoms, making it difficult for beekeepers to spot the problem early. Alert beekeepers may notice that their bees are finding it difficult to fly and that there is excreta on the combs or dead/dying bees on the ground around the hive. However, these can also be symptoms of other diseases or pests, meaning that a correct diagnosis of the problem can be delayed.

So, as you have probably figured out by now, nosema disease can cause many symptoms and problems for honeybees, but none of these symptoms are specific to nosema disease. The only accurate way to detect nosema disease is with a lab examination.

If you do spot bees crawling around the front of your hive, check inside for other symptoms, such as dysentery (brown diarrhea in the case of bees). You will likely find this on the combs or even outside the hive. Be aware however that nosema disease does not actually cause dysentery, although infected honeybees are more susceptible to other infections that in turn can result in dysentery.

What to Do If You Suspect Nosema Disease

If you are worried that your colony might be infected with nosema disease, it is vital that you act fast. As mentioned above, the only way to be sure is with laboratory examination. The gut of a sample of bees must be examined under a 400x microscope.

What you can do beforehand is take a look at the gut of one of your dead bees. To do this, expose the gut by holding firmly on the stinger and pulling off the head. A healthy midgut will have a tan color and a ringed appearance that is similar to the body of an earthworm. If the gut is affected with nosema disease it will be less segmented, an off-white color, and may be swollen. If you notice any of these signs, it is time for a closer look under a microscope.

How to Treat Nosema Disease

As with everything else bee related, in the case of Nosema disease prevention (or management) is better than cure. To help prevent, or at least curb, the spread of nosema disease, it is best to be vigilant and take specific measures. Beekeepers should also send samples away for inspection every spring to ensure potential disease is spotted as early as possible.

This is a precautionary measure but if you do this, you will be able to implement other measures as early as possible.

You should also change combs regularly and make sure that you do not transfer combs from one hive to another. Promoting queens with high resistance levels is also wise, as is using feed supplements that can help with keeping disease levels low and creating stronger colonies. A strong colony is considered the best way to keep nosema levels at bay.

It is also important to reduce stress on your bees. One way to do this is by limiting or avoiding hive inspections and movements during the winter.

Some beekeepers prefer to use chemical treatment for nosema disease. Fumagillin is one such treatment that has been used, but research suggests that this chemical is not as affective at treating infections caused by Nosema ceranae.


Nosema disease has often been referred to as the ‘silent killer’ of the honeybee due to the fact that it has no specific symptoms that makes it easy to identify. So as mentioned above, the best way to manage and control nosema disease is by creating and maintaining a strong colony. And ensure your hives are well prepared for the winter with a good supply of honey.

Make sure your apiary site is protected from cold winds and that hives are placed in a sunny position in the winter. Hives placed in (winter) sun traps see a significant reduction in nosema infection. Ensuring the hive gets the maximum sun and shelter over winter can help prevent this deadly disease taking hold within your hive.


Anthony is a content creator by profession but beekeeping is one of his great passions.

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