Bee Health

Healthy Bees

Just like all living organisms, Honey Bees need to be kept healthy in order to be productive. The main role of the Beekeeper during a Hive inspection is to make sure that the colony is healthy before any other considerations can be taken.

There are three main checks that can be made to make sure that the colony is healthy:-


A healthy colony with a Queen should have lots of visible eggs during the summer months. They will look like a tiny grain of rice, about 1.5mm long and should be white in colour, as can been seen in the image below:-

A Queen will only lay one egg in each cell, but sometimes if the Queen is old, dead or missing then some workers can begin to lay eggs as well. This is because the Queen's pheromones that stop the workers laying begin to run out. If there are laying workers, there will be multiple eggs within one cell, as can be seen in the image below:-


An egg takes 3 days to hatch to become a larva and then it takes another 6 days before a worker larva is "capped" (sealed within the cell with a wax lid), so in a healthy colony there should be roughly twice as many larvae visible than eggs.

Healthy larvae are pearly white in colour and should be lying comfortably curled up at the bottom of the cell, as can be seen in the image below:-

Sealed Brood (Pupae)

Once the larvae are ready to pupate, the worker bees seal the cell with a wax cap, so they are referred to as "sealed brood". As before, as it takes twice as long to pupate than as a larvae, a healthy colony should contain roughly twice as many sealed brood as larvae.

Healthy sealed brood should be uniform in colour (slightly off white) and be slightly domed for workers, or more pronounced domes for drones. The image below shows sealed brood for workers and drones:-

Bee Diseases

Bee diseases can be split into two groups; diseases of the brood (developing bees) and diseases of the adult bee. All diseases will caused problems for the colony, but some are more severe than others.

There are two diseases that must be reported by law if they are found in Scotland; American Foul-Brood and European Foul-Brood. For further information please see - Scottish Government AFB + EFB Advice

Brood Diseases

American Foul-Brood (AFB)

American Foul-Brood is caused by a Bacteria called Paenibacillus larvae. The AFB bacteria grow in the bee's digestive system whilst it is a larvae and kills it once it is capped and stars to pupate.

When worker bees clean out the dead pupa, millions of spores are released and can be spread to the rest of the colony.

These spores are extremely hardy and it is therefore incredibly difficult to control an outbreak of AFB; in fact in Scotland the colony would be destroyed.

The symptoms to watch for within a colony are:

  1. Sunken/broken Cappings which look greasy.

  2. A "peppered" appearance to the brood, where cells are randomly uncapped.

  3. sticky larval remains which can be drawn out with a matchstick (ropiness test).

Peppered Brood

Sunken & Broken caps

Sticky larval remains

If AFB is found within a colony, the local Bee inspector must be informed by law. The Bee inspector will then seal up the colony, and kill the bees using petrol. The contents of the hive are then burned in a pit at night (to prevent robber bees stealing from the remains) and buried. The image below shows a hive being burned following a discovery of AFB:-

European Foul-Brood (EFB)

Like American Foul-Brood, European Foul-Brood is caused by a Bacteria, this time by Melissococcus Plutonius. The EFB bacteria again infect the larvae through their food, but unlike AFB, in EFB the larvae die before they are capped. The dead yellowish coloured larvae can bee seen lying in uncomfortably twisted positions within the open cell.

Because the EFB bacteria doesn't form spores it is easier to destroy than AFB, but it still must be reported to the Bee inspector.

The symptoms to watch for within a colony are:

  1. Infected larvae lie in awkward positions in cell.

  2. Dead larvae look melted and yellow brown in colour.

  3. Dried larval remains form "scales" that can be easily removed from cells.

Note - The "ropiness test" will not work for EFB.

Dead yellowed larvae

Dried Larval scales

If EFB is found within a colony, the local Bee inspector must again be informed by law. The Bee inspector will make a decision whether to destroy the colony or not. If the colony has a severe outbreak, it is destroyed using the same methods as AFB - killed with petrol then burned.

If the outbreak is mild, it is possible to save the colony by using the "shook swarm" method, where the adult bees are moved to a clean disease free hive, leaving behind the infected larvae. This can only be done with the consent and assistance of the Bee inspector.


Chalkbrood is a disease caused by a fungus - Ascosphaera apis. Chalkbrood is a disease that kills the larvae after they have been sealed within the cell. It is called Chalkbrood as the dead larvae take on a chalky white mummified appearance after death. Chalkbrood is spread by fungal spores on adult bees or on old comb (which is why this should be regularly replaced).

Chalkbrood is not usually a severe disease, but should be kept under control by replacing the comb. Whilst there is no treatment, it usually clears up naturally during the warm summer weather.

Mummified remains

Chalkbrood within comb

Sac Brood

Sacbrood is caused by the sacbrood virus (a type of iflavirus) which infects the larvae and kills it once it has been capped. The virus stops the larvae moulting and leave the dead larvae within a fluid filled sac.

Sacbrood does not usually affect many cells in a colony and generally clears up without treatment, but re-queening from a clean hive can help.

Sacbrood within comb

Larva within a sac

Deformed Wing Virus (DWV)

Deformed Wing Virus is a virus that is endemic (found in all) in Bees without causing any issues. However, if the colony is weakened by large numbers of Varroa mites, then the virus can manifest itself. DWV causes the wings of the developing pupae not to form properly. This means that they are small and unable to be used for flying. If too many Bees are unable to forage due to this, the colony can fail.

Healthy vs DWV

Chronic Bee Paralysis Virus (CBPV)

Like DWV, Chronic Bee Paralysis Virus is endemic in Bees without causing any issues. Again, however, if the colony is weakened by large numbers of Varroa mites, then the CBPV virus can manifest itself. Bees suffering from CBPV are shiny and black in colour, as they have lost all of their body hair. They cannot fly, and usually are found trembling, crawling around the top bar of the hive or on the floor.

There is no treatment for CBPV, but strong colonies usually recover naturally, especially if the Varroa mite load is reduced.

Healthy vs cbpv

Adult Bee diseases


Just like other animals, Bee can suffer from Dysentery. This can be seen as brown stains on the comb or at the hive entrance. It can be caused by a number of factors:-

  1. Prolonged wet weather in spring - If the bees are unable to leave the hive to make cleansing flights, they have to defecate within the hive itself.

  2. Nosema apis infection - This parasite affects the digestive system of the Bee. It is carried by spores, which are found in cold, damp hives. The infection usually disappears in warm weather.

  3. Amoeba disease - Like Nosema, this protozoan affect the digestive system of the Bee causing dysentery. Moving the Bees to clean comb can reduce the effect of this amoeba.

Brown stains on comb

Brown stains on hive

Tracheal mites

Tracheal mites are microscopic (~0.2mm) mites that can infest the Trachea of Bees. The mites reproduce in the Trachea and feed off the Bee's haemolymph (an insect's equivalent of blood). This weakens the bees and reduces their work efforts and lifespan. A large enough infestation can kill a colony.

There is no treatment for Tracheal mites that are legal in the UK, so the only option is requeening the colony with a less susceptible Queen.

A Tracheal mite

Mites within a trachea

Varroa Mites

Varroa mites are the number one concern affecting Beekeeping in Scotland. The Varroa Mite has its own section on this website:-

Varroa Mites


Honey Bee colonies are also affected by certain pests that can risk the survival of the colony. A well constructed hive is designed to protect the colony from these intruders.


Mice can cause a large issue to a Honey Bee colony due to the damage they can cause to the comb. Bee hives are attractive to mice as they are warm and have a huge food supply for the mouse.

Sometimes, when the bees are in their cluster they do not notice the mouse in their house. Mice can sometimes co-exist with bees for quite some time. Other times, mice are not so lucky. Once discovered, the bees can sting them to death, encapsulate the body with propolis (bee glue) and wall it off. Mice can be kept out of the hive by mouse guards at the entrances, and by making sure there are no gaps in the walls.

Sometimes the mouse wins

Sometimes the Bees win

Wax Moths

Wax Moths lay their eggs within Honey Bee colonies to provide their larvae with a food source. When the larvae hatch they tunnel through the comb, eating wax, honey and Bee larvae. This can quickly destroy large areas of comb. A healthy colony will quickly destroy these invaders, but a weaken colony can be destroyed.

If wax moth larvae are found, they larvae should be removed and the affected comb should be destroyed.

Adult wax moth

Wax moth larvae with silk

Small hive beetle

The Small Hive Beetle is originally from Africa but now can be found in the US and Australia. The Small Hive Beetle is a black beetle, about 6mm long with clubbed antennae. The beetles lay their eggs within the colony, then the larvae tunnel through the comb to feed on Bee eggs and brood, leaving slime all over the comb.

It so far has not been found in the UK, but it is has notifiable pest status so Beekeepers should still be aware of it.

An adult Small Hive Beetle

Beetle larvae & slime

Braula (Bee Louse)

Braula are small wingless insects from the Fly family. The adults are small (slightly smaller than the head of a pin), reddish brown in color. The colouration and size is similar to the Varroa mite however Braula have six legs, while varroa have eight legs. While several adults are often seen on a queen, usually only one will be found per worker.

These do little harm to the Bees, but the larvae disfigure comb by burrowing through cappings. They are not parasitic, they merely steal food from the Worker Bees.

Since the arrival of Varroa mites and the routine treatment with micicides, Braula is no longer present in Scotland as it succumbs to most miticides. The exception to this is the Native Honey Bees on the isle of Colonsay, as the Island is Varroa-free, and so not miticide treatments have been used.

Braula on a Worker

Damage caused by Burrowing


Wasps can be a major threat to Honey Bee colonies. Common European Hornets will steal honey stores, eat larvae and eggs and can kill adult bees. The best way to prevent this is to make sure that there are no gaps anywhere in the hive, so the Bees only have to defend the main entrance.

The video below shows how worker bees can remove a wasp from the hive as well as how Beekeepers can control wasp numbers:-


Neonicotinoids are a class of pesticides (chemicals that are used to kill insects and other pests) that have been used widely to protect crops from damage. These pesticides have a similar chemical structure to Nicotine, and affect the body in a similar way. When the insect takes in the Neonicotinoids, they bind to parts of the nervous system blocking parts of it. In a large enough dose, this causes paralysis and death.

They are very effective because they are systemic. This means that the Neonicotinoids can be added to water and the crops will take it up are spread it through the entire plant. This is better than traditional spraying, as if you then water the plants, the sprayed chemical is washed off the plants.

It is this systemic approach that is the problem for Bees. The Neonicotinoids enter the Nectar of the flowers, and therefore the Bees will also ingest it. This is made worse by Bees then favouring flowers with Neonicotinoids in their nectar, just like a smoker addicted to cigarettes.

The level of Neonicotinoids in the nectar is low, so doesn't generally kill the Bee instantly,but has been shown to have the following long term effects:-

  1. Lower life expectancy

  2. reduced flying ability

  3. Ability to learn navigational directions

  4. Lower resistance to viruses

  5. Lower resistance to Mite infestations

  6. Colonies at greater risk of Colony Collapse Disorder (where otherwise healthy colonies fail unexpectedly)

Neonicotinoids have been banned for use in the UK since 2013 under EU law, in an effort to protect Bees and other natural pollinators, but this has had a negative impact on farming, so is a controversial issue that may be reviewed after Brexit.

The video below shows a summary of the importance of Bees and the threats to their health:-

Sending Bees for testing

Within Scotland, it is possible to send a sample of Bees to be tested for diseases under laboratory conditions.

The testing body in Scotland is "Science & Advice for Scottish agriculture" (SASA), which part of the Scottish Government. SASA's primary role is to provide scientific services and advice in support of Scotland’s agriculture and wider environment.

In cases of colony loss, it is recommend that beekeepers carries out a basic hive ‘post mortem’. This should involve checking for common issues such as Queen problems, starvation and Varroa control.

Should the reason for the colony loss remain unclear after this examination, SASA offers a limited service where a sample of adult bees is examined for the presence of Acarine mites, Nosema and evidence of Varroa damage.

Whilst the results of these tests often provide no further reason for colony loss to the beekeeper the information gathered from these samples allows SASA to monitor for trends in native pests and diseases, and to check for new threats to Scottish beekeeping.

Incidents of suspected poisoning of animals (including bees) by pesticides in Scotland are investigated by SASA’s Wildlife Incident Investigation Scheme (WIIS).

Submitting a sample for analysis

The adult bees sampled should be as fresh as possible, contain a minimum of 30 bees, and be packaged in a crush resistant container, preferably cardboard. If a plastic container is used, then the bees should be wrapped in kitchen paper to prevent them degrading in transit.

Samples should be clearly labelled with the hive identifier and sent to "Bee Diseases" at the address shown below. Please remember to include your own contact details for reporting of results and any information pertinent to the analysis. This may include the strength of the colony, management and treatment, and any unusual symptoms noted prior to the loss.

The information below (also hyperlinked) are the contact details for SASA:-

Collecting ~30 Worker Bees for analysis

The method is a humane way of collecting a sample of approximately thirty Honey Bees. You will need a small plastic bag. A little “zip-lock” bag is perfect, but a small food bag or coin bag will be fine. You will also need a short tube. Alternatively, the outer sleeve of a matchbox, short piece of plastics pipe or a piece of rolled up card would be fine too.

The opening of the tube is moved around the top of the brood frames. The Bees’ instinct is to go “up and into the dark”. A number will investigate the inside of the dark tube and walk into the bag. You will be able to see Bees in the bag and inside the tube. Take your time and be gentle. The idea is to let them investigate and not to push them in.

Once there are approximately thirty bees in the bag and tube carry out a single, smooth, swift action, to do the following:

  1. Turn the bag/tube upside down.

  2. Give a single downward jolt to dislodge any bees in the tube into the bottom of the bag.

  3. Remove the tube and seal the bag.

The result should be a sample of approximately thirty bees, which can be used for adult honey bee disease diagnosis.

Note - It is VITAL to check that the Queen has not ended up in the test bag!

It is unfortunately necessary to kill the sample of bees to test for diseases. One of the simplest and most humane ways of doing this is to put the sample into the freezer overnight at -18°C.