Understanding the Varroa Mite: What Every UK Beginner Must Know

If you are setting up your first hive in a British back garden, allotment, or smallholding, there is one threat that will follow your bees from the moment you acquire them to the last season you keep them. Varroa destructor — the varroa mite — is present in virtually every managed honeybee colony in the United Kingdom. It has been established here since the late 1980s, and there is no realistic prospect of eradicating it from the national bee population. Understanding what it is, what it does, and how to manage it is not an optional extra for the enthusiastic beginner. It is the foundation of responsible beekeeping.

This article will give you a thorough grounding in varroa biology, the damage it causes, how to monitor mite levels in your hive, and the range of treatments available to UK beekeepers. The British Beekeepers Association (BBKA) and the National Bee Unit (NBU), which operates under the Animal and Plant Health Agency (APHA), produce excellent guidance, and both are worth bookmarking from your very first season.

What Exactly Is the Varroa Mite?

Varroa destructor is an external parasitic mite that feeds on honeybees. It is reddish-brown in colour, roughly 1.5mm wide and 1.1mm long — just about visible to the naked eye if you know what you are looking for. The mite originally parasitised the Asian honeybee, Apis cerana, which has evolved behavioural defences against it over thousands of years. Our Western honeybee, Apis mellifera, has no such evolutionary history with the mite, which is why varroa causes such devastation in unmanaged colonies.

The mite’s lifecycle is intimately tied to the bee’s own reproductive cycle, and this is what makes it so difficult to control. A female mite — called a foundress mite — enters a brood cell just before it is capped, hiding in the brood food beneath the developing larva. Once the cell is sealed, she begins laying eggs. Her first egg produces a male; subsequent eggs produce females. The male mite mates with his sisters inside the cell (yes, this is inbreeding, and yes, it is normal for varroa). By the time the young bee chews its way out of the cell, at least one or two new mated female mites emerge with it, ready to repeat the cycle.

Worker bee cells are capped for around 12 days. Drone cells, which are capped for roughly 14 to 15 days, are even more attractive to varroa because the longer capping period allows more reproductive cycles. This is an important detail you will use when it comes to management strategies.

Why Varroa Is So Damaging

The mite causes harm in two distinct but related ways. First, it feeds directly on the fat body of the developing bee — a critical organ involved in immunity, nutrient storage, and overwintering capacity. Bees that emerge from heavily infested cells are smaller, shorter-lived, and immunologically compromised. You may see adult bees with deformed, shrivelled wings crawling at the hive entrance — a classic sign of a colony under severe mite pressure.

Second, and arguably more seriously, varroa acts as a vector for viruses. Deformed Wing Virus (DWV) is the most significant. In healthy, low-mite colonies, DWV circulates at low levels and causes little visible harm. But when varroa feeds on larvae and injects the virus directly into the haemolymph, viral titres can rise dramatically. Other viruses transmitted by varroa include Sacbrood virus, Black Queen Cell Virus, and Acute Bee Paralysis Virus. A colony dealing with high varroa loads is essentially a colony in a state of chronic viral infection, and its population will decline rapidly — often collapsing before winter or failing to build up again in spring.

Left untreated, a colony with varroa will typically collapse within two to three years. This is not a hypothetical — it has been demonstrated repeatedly in studies and is observed regularly when swarms establish in unmanaged locations such as chimneys or hollow trees.

Monitoring Mite Levels: The Non-Negotiable First Step

Before you treat, you need to know what you are dealing with. Treating blindly wastes money, risks chemical resistance developing in the mite population, and may harm your bees unnecessarily. The NBU recommends monitoring at least once a month during the active season, and most experienced beekeepers do it every time they open the hive.

The Alcohol Wash (Sugar Roll)

The alcohol wash — sometimes called the sugar roll when done with icing sugar instead of alcohol — is considered the most reliable method for quantifying varroa levels in adult bees. To perform an alcohol wash, take a sample of approximately 300 bees (roughly half a cup) from a brood frame — making absolutely certain the queen is not among them. Place the bees in a jar with a mesh lid, add isopropyl alcohol or methylated spirits, and shake vigorously for 60 seconds. The mites detach from the bees and fall through the mesh into a white tray where you can count them.

Divide the number of mites by the number of bees in your sample to get a percentage infestation rate. The NBU’s recommended threshold for treatment is around 1,000 mites per colony, but because counting every mite is impractical, a sample infestation rate of 1% or above in the summer months generally indicates that treatment is warranted. Some beekeepers use a threshold as low as 0.5% during the brood-rearing season.

The Sticky Board (Varroa Floor)

Most modern National hives and WBC hives sold in the UK come fitted with an open mesh floor and a removable sticky monitoring board. Slide the board in for 24 to 72 hours and count the number of mites that have fallen naturally. Divide by the number of days to get a daily mite drop figure. As a rough guide, a natural daily drop of more than 10 mites in summer suggests a significant infestation requiring attention. However, the sticky board is less precise than the alcohol wash because mite drop rates vary with colony activity, time of year, and hive temperature. Use it as a screening tool rather than a definitive count.

Uncapping Drone Brood

Because drone brood is preferentially parasitised, examining a sample of capped drone cells is a quick and cheap way to get a rough picture of mite levels. Use your uncapping fork or a cappings scratcher to pierce and pull out drone pupae from a section of capped drone comb. Examine the pupae and the wax cappings for mites — they will appear as reddish-brown specks against the pale pupae. This method is qualitative rather than quantitative, but if you are seeing mites on a high proportion of pupae, act promptly.

Integrated Pest Management: The Correct Approach

Varroa management is not a single action taken once a year. It is an ongoing programme combining monitoring, cultural controls, and targeted treatments — a strategy known as Integrated Pest Management (IPM). The goal is to keep mite populations below the threshold at which they cause significant harm, without applying treatments more than necessary.

Biotechnical Controls

These are management techniques that exploit the mite’s biology without using chemicals.

Brood breaks: Because varroa can only reproduce in capped brood, periods without brood — either naturally at the end of the season or artificially induced by caging the queen — force all mites onto adult bees where they are far more vulnerable to treatment. A brood break of at least 23 days (the lifespan of worker brood from egg to emergence) will ensure no mites are reproducing. This is one of the most powerful tools available and is strongly recommended in autumn before applying oxalic acid treatment.
Drone brood removal: Because mites preferentially infest drone brood at a rate five to eight times higher than worker brood, inserting a drone comb foundation frame, allowing it to be built out and filled with drone brood, and then removing and freezing the capped drone comb removes a disproportionate number of mites from the system. This is a useful spring and summer technique to slow mite population growth. It does require you to destroy the developing drone brood, which some beekeepers find uncomfortable at first, but it is a well-established and effective method.
Swarm control: When a colony swarms, the original hive is left with no emerging brood for several weeks while new queen cells develop and a virgin queen mates. This natural brood break temporarily halts mite reproduction, offering a good treatment window. Good swarm control management therefore serves double duty.

Approved Chemical Treatments

The UK has a range of licensed varroa treatments available to amateur beekeepers. All treatments should be used strictly in accordance with their product licences, and it is important to rotate between different active ingredients to reduce the risk of resistance developing.

Oxalic acid (Api-Bioxal): This is the most important treatment available to UK beekeepers. Oxalic acid is a naturally occurring organic acid found in plants such as rhubarb and spinach. Applied correctly, it has extremely low toxicity to adult bees and leaves no residue in honey. It is highly effective against phoretic mites (mites on adult bees) but has no efficacy against mites inside capped brood. This is why it works best during a brood break. It can be applied by trickling a warm syrup solution directly onto bees between the frames (the standard method for amateur beekeepers), or by sublimation (vaporisation) using a specialised device. Sublimation is more effective over multiple applications but requires additional safety equipment including a respirator rated for organic vapours and protective eyewear. Sublimation vaporisers are available from most UK beekeeping suppliers including Thorne’s, Abelo, and Maisemore’s.