Understanding the Varroa Mite: What Every UK Beginner Must Know
If you have recently set up your first hive, joined a local beekeeping association, or are still in the planning stages of keeping bees in the UK, there is one topic that will come up again and again in every conversation, every workshop, and every online forum you encounter: Varroa destructor. The Varroa mite is not a distant threat or a worst-case scenario. It is a biological reality of modern beekeeping in Britain, and understanding it thoroughly before your first season is one of the most important things you can do to give your colony a fighting chance.
This article covers what Varroa actually is, how it damages colonies, how to monitor it, and what treatment options are available to UK beekeepers. None of this needs to feel overwhelming. Thousands of hobbyist beekeepers across England, Scotland, Wales, and Northern Ireland manage Varroa successfully every year with straightforward, affordable methods.
What Is Varroa destructor?
Varroa destructor is an external parasitic mite that feeds on honey bees. Originally a parasite of the Asian honey bee (Apis cerana), it transferred to the Western honey bee (Apis mellifera) — the species kept by most UK beekeepers — during the twentieth century and has since spread to almost every country in the world. It was confirmed in the UK in 1992, and there are currently no Varroa-free areas on the British mainland, though the Isle of Man and some Scottish islands have maintained Varroa-free status through strict biosecurity measures.
The mite is visible to the naked eye, though only just. An adult female Varroa mite is roughly 1.5mm wide and 1.1mm long — oval, reddish-brown, and flat. You can see them on adult bees if you know what to look for, though their preferred habitat is inside capped brood cells, which makes monitoring slightly more involved than simply peering at your bees through the crown board.
Why Varroa Is So Damaging
The mite causes harm in two distinct but related ways, and understanding both helps explain why a seemingly small infestation can bring down a colony within a season or two if left unchecked.
Direct Physical Damage
The female mite enters a brood cell just before it is capped — preferably a drone cell, which has a longer capping period and thus more time for reproduction, though worker cells are also used. Once inside, she feeds on the fat body of the developing bee larva and pupa. This feeding causes direct physical harm, reducing the adult bee’s body weight, shortening its lifespan, and impairing the development of its wings, abdomen, and hypopharyngeal glands (which are critical for producing royal jelly and feeding young larvae). Bees that emerge from mite-infested cells are often visibly deformed — stunted, with crumpled or missing wings. This condition is so common it has its own name: Deformed Wing Virus, which brings us to the second, and arguably more serious, problem.
Viral Transmission
Varroa is an extremely efficient vector for bee viruses. Deformed Wing Virus (DWV) is the most significant, but the mite also transmits Sacbrood Virus, Acute Bee Paralysis Virus (ABPV), and several others. When the mite feeds, it injects viral particles directly into the developing bee’s haemolymph (blood). A colony under significant Varroa pressure quickly becomes riddled with viral disease, even when individual mite counts seem relatively modest. Research from the Food and Environment Research Agency (now part of FERA Science) and the National Bee Unit has demonstrated that viral loads in colonies with even moderate Varroa infestations can be orders of magnitude higher than in uninfested colonies.
The combination of direct physical harm, suppressed immune function, and rampant viral transmission means that a colony can collapse with alarming speed once the mite population passes a critical threshold — typically in late summer and early autumn, when bee numbers are falling but mite numbers, having reproduced throughout the summer brood cycle, are at their peak.
The Varroa Reproductive Cycle
To manage Varroa effectively, it helps to understand how it reproduces, because every treatment strategy in the beekeeper’s toolkit is designed to disrupt this cycle at one point or another.
The foundress mite (a mated female) enters a brood cell and hides in the larval food just before the cell is capped. After capping, she begins to feed and lays her first egg — which is always male and unfertilised — approximately 60 hours later. She then lays female eggs at roughly 30-hour intervals. The male mite develops first and mates with his sisters inside the cell before the adult bee emerges. Only mated female offspring leave the cell with the emerging bee; the male and any unmated females die inside.
On average, a single reproductive cycle produces approximately 1.45 new mated females per worker cell and up to 2.2 per drone cell. The population of mites in a colony therefore grows exponentially throughout the spring and summer, as new bees are constantly being reared and mites are constantly reproducing inside the capped brood. This is why autumn — when brood rearing slows and the mite-to-bee ratio skyrockets — is the most dangerous time for colonies with uncontrolled infestations.
How to Monitor Varroa Levels in Your Hive
Monitoring is not optional. Without a reliable picture of your mite load, you are guessing — and guessing in one direction means treating unnecessarily, while guessing in the other means watching your colony die. There are several practical methods available to UK beekeepers, and you do not need expensive equipment for any of them.
The Varroa Tray (Natural Mite Drop)
Most modern National hives — the most common hive type in the UK — come with an open mesh floor and a white corrugated plastic insert known as the Varroa tray or monitoring board. When slid into position beneath the mesh floor, it catches mites that fall naturally from bees and from brood cells. After 24 hours (or, for a more reliable average, 7 days divided by 7), you count the mites visible as tiny reddish-brown specks on the white surface.
A natural daily mite drop of fewer than 6 mites in the spring and summer generally indicates a manageable infestation. A drop above 10 in early spring or above 6 in autumn warrants prompt treatment. These are rough guidelines used by the National Bee Unit (NBU), and they vary depending on colony size, season, and local conditions — but they give you a starting point. The NBU’s BeeBase website, which is free to access and highly recommended for all UK beekeepers, provides detailed guidance on interpreting mite drop counts alongside interactive tools and regional disease alerts.
Alcohol Wash (Wash and Count)
The alcohol wash is more accurate than natural mite drop and is considered the gold standard for monitoring. You collect approximately 300 bees (roughly half a cup) — always from brood frames, never the queen — place them in a jar with a mesh lid, add surgical spirit or methylated spirits, and agitate vigorously for 30 to 60 seconds. The alcohol kills and dislodges mites from the bees’ bodies. You then pour the liquid through the mesh into a white tray and count the mites.
A mite count of 1 or 2 per 100 bees (so 3–6 in a sample of 300) is generally considered the treatment threshold during the active season. Above this level, treatment should be implemented without delay. Yes, the process kills the sample of bees, which some beginners find distressing — but 300 bees represent a tiny fraction of a colony of 40,000 to 60,000, and the information it provides is invaluable.
Icing Sugar Roll
The icing sugar roll is a non-lethal alternative. Bees are placed in a jar with icing sugar, rolled to coat them thoroughly, and then shaken over a white sheet. Mites temporarily dislodged by the sugar are counted. It is less accurate than the alcohol wash and tends to undercount significantly, but it is useful for beekeepers who prefer not to sacrifice bees during sampling.
Treatment Options Available to UK Beekeepers
The UK has a limited but effective range of Varroa treatments, all of which are licensed through the Veterinary Medicines Directorate (VMD). It is a legal requirement to use only licensed products for Varroa treatment in the UK, and the NBU recommends rotating between different treatment types to reduce the risk of resistance developing.
Oxalic Acid (Apivar OA, Api-Bioxal)
Oxalic acid is a naturally occurring compound found in rhubarb, spinach, and other plants. It is highly effective against phoretic mites (those riding on adult bees) but has no effect on mites inside capped brood cells. This characteristic makes it most effective during the broodless period in winter, when all mites are phoretic.
In the UK, oxalic acid is licensed in two forms: as a trickle treatment (a warm syrup solution poured directly between frames over bees) and as a vapour treatment using a purpose-built vaporiser. Vaporisation is generally considered more effective and causes less disturbance to the winter cluster, but vaporisers must be used with appropriate respiratory protection, as oxalic acid vapour is harmful to humans. A single oxalic acid treatment applied correctly during a broodless period in December or January can reduce mite populations by over 90%.
Apistan (Tau-Fluvalinate)
Apistan strips are plastic strips impregnated with tau-fluvalinate, a synthetic pyrethroid. The strips are hung between the frames, and bees pick up the chemical as they pass. Apistan has been used in the UK since the 1990s, and widespread resistance has developed in many areas. Before using Apistan, it is worth checking with your local Bee Inspector or beekeeping association whether resistance is prevalent in your region — in many parts of England, Apistan is now largely ineffective.