Understanding the Varroa Mite: What Every UK Beginner Must Know

If you are new to beekeeping in the United Kingdom, you will hear the name Varroa destructor repeated at every local association meeting, every training course, and in virtually every beekeeping book you pick up. That repetition is entirely justified. The Varroa mite is, without exaggeration, the single greatest threat facing honey bee colonies in Britain today, and it has been since it arrived on these shores in the late 1980s. Understanding what it is, how it behaves, and how to manage it is not optional knowledge for the hobbyist beekeeper — it is the foundation upon which healthy colonies and successful honey harvests are built.

This guide is written specifically for beginners setting up their first hives in the UK. It covers the biology of the mite, how to recognise an infestation, how to monitor mite levels accurately, and the full range of treatment options available under British regulations. By the end, you will be equipped to make informed decisions that keep your bees alive and thriving through every season.

What Exactly Is Varroa?

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 virtually all UK beekeepers — during the twentieth century. The problem is that Apis cerana evolved alongside Varroa over thousands of years and developed natural behavioural defences against it. Our European honey bees have no such evolutionary history and are largely defenceless without human intervention.

Adult female mites are reddish-brown, oval-shaped, and roughly 1.1mm wide by 1.6mm long. They are just about visible to the naked eye on a bee’s body, though spotting them in a busy colony without a systematic approach is difficult. Male mites are smaller and paler and die shortly after mating inside a capped cell. It is the female mite that does the damage.

How the Mite Reproduces

Understanding the Varroa reproductive cycle is essential because it directly shapes how and when treatments work. A mated female mite — known as a foundress — enters a brood cell just before it is capped. She hides beneath the larval food and waits. Once the cell is sealed, she begins to feed on the developing pupa and lays her first, unfertilised egg, which becomes a male. She then lays several fertilised eggs at roughly 30-hour intervals, each of which becomes a female.

The mites mate inside the capped cell. When the adult bee emerges, the foundress and her mature daughters ride out with it, ready to infest new cells. Worker brood has a capping period of about 12 days; drone brood is capped for roughly 14 days. Because Varroa prefers drone brood — producing more offspring per cycle due to the longer capping period — drone cells are disproportionately infested. This preference is something beekeepers can exploit in their management strategy.

A single mite left untreated can lead to exponential population growth within a colony. Research from the National Bee Unit (NBU) in the UK estimates that under warm summer conditions, Varroa populations can double every four to six weeks. A colony that carries a seemingly manageable mite load in June can be collapsing by September.

Why Varroa Is So Damaging

The mite causes harm in two distinct but compounding ways. The first is direct physical damage. Varroa feeds on the fat bodies of developing pupae rather than, as was previously believed, haemolymph (bee blood). The fat body is critical to bee health — it is involved in immune function, pesticide detoxification, protein synthesis, and overwintering survival. Bees that emerge from infested cells are often smaller, have shorter lifespans, and show reduced learning and foraging ability.

The second, and arguably more serious, harm is viral transmission. Varroa acts as a vector for a range of bee viruses. Deformed Wing Virus (DWV) is the most significant. Bees infected with DWV as pupae may emerge with crumpled, shrivelled wings and distended abdomens, rendering them unable to fly. They typically die within days. Other viruses spread by Varroa include Sacbrood virus, Acute Bee Paralysis Virus (ABPV), and Chronic Bee Paralysis Virus (CBPV). A heavily infested colony can carry viral loads many thousands of times higher than an uninfested one.

Left unmanaged, a Varroa-infested colony in the UK typically collapses within two to three years. This is not a gradual decline that a beekeeper can easily reverse — by the time the visible signs of serious infestation appear, the colony may already be beyond saving.

Recognising the Signs of Infestation

As a beginner, learning to read your colony is one of the most valuable skills you can develop. Varroa infestation does not always announce itself dramatically. Early on, there are few obvious signs. As the infestation grows, you may begin to notice the following:

Bees with deformed or stumpy wings crawling on the landing board or around the base of the hive — a classic sign of Deformed Wing Virus.
A patchy or “shotgun” brood pattern, where capped cells are interspersed with empty cells or sunken, discoloured cappings.
A reduction in the overall adult bee population relative to the time of year, sometimes called “dwindling”.
Bees that appear lethargic, shaky, or that crawl rather than fly.
Mites visible on adult bees, particularly on the underside of the abdomen between the tergites (the hard plates on the bee’s back).

However, by the time these symptoms are obvious, the infestation has usually become serious. The only reliable way to stay ahead of Varroa is through regular, systematic monitoring — not waiting for symptoms to appear.

Monitoring Mite Levels

The National Bee Unit, which operates under the Animal and Plant Health Agency (APHA) and offers free inspections to UK beekeepers through its BeeBase programme, recommends monitoring colonies at least monthly during the active season, and always before and after any treatment. There are three main monitoring methods available to the hobby beekeeper.

The Natural Mite Drop (Sticky Board)

A mesh-floored hive fitted with a white or yellow sticky board (also called a varroa floor or monitoring board) inserted beneath the mesh allows you to count mites that fall naturally from the colony. Insert the board for a set period — typically 24 hours or seven days — and count the mites. The Natural Mite Drop gives a general indication of mite levels but is considered the least accurate monitoring method because natural fall rates vary with temperature, colony activity, and treatment residues. A result of more than one or two mites per day during summer warrants closer investigation.

Alcohol Wash

This is widely regarded as the most accurate method and is recommended by the NBU. A sample of approximately 300 adult bees (roughly half a cup) is collected from a brood frame — avoiding the queen — and placed into a jar with a mesh lid. A small amount of methylated spirit or surgical spirit is added, the jar is shaken vigorously for about a minute, and the liquid is poured through the mesh into a white tray. The mites, being dislodged by the alcohol, are visible in the tray and can be counted. The percentage of mites in the sample gives a reliable picture of overall infestation.

A mite count of 3% or above (i.e., 9 or more mites in a 300-bee sample) generally indicates that treatment is needed. The alcohol wash does kill the sampled bees, which puts some beginners off, but 300 bees represents a tiny fraction of a healthy colony and is a worthwhile sacrifice for accurate data.

Sugar Roll

The sugar roll is a non-lethal alternative to the alcohol wash. A similar bee sample is placed in a jar with icing sugar, rolled to coat the bees, and then the sugar is shaken out through a mesh into a tray of water. Mites detach along with the sugar and can be counted. The sugar roll is gentler on the bees but is generally considered somewhat less accurate than the alcohol wash, as not all mites are dislodged.

Treatment Options Available in the UK

This is where UK beekeepers have a clearly defined set of tools, all of which must be used in accordance with the product’s veterinary authorisation. It is important to understand that only treatments with a UK veterinary product authorisation should be used. Using unauthorised products, or misusing authorised ones, risks bee health, honey contamination, and potentially breaking the law. The Veterinary Medicines Directorate (VMD) maintains the current register of authorised treatments.

Oxalic Acid

Oxalic acid (OA) is a naturally occurring organic acid and is the most widely used Varroa treatment amongst UK hobby beekeepers. It is effective against phoretic mites — those riding on adult bees — but has no effect on mites inside capped brood. This means it is most effective when applied during a broodless period, either in midwinter when the queen has naturally stopped laying, or during an artificially induced brood break.

In the UK, oxalic acid is available as Api-Bioxal, which is the only veterinary-authorised oxalic acid product. It can be applied in three ways:

Trickle (dribble) method: A warm solution of oxalic acid in sugar syrup is trickled directly over the bees on each seam of the cluster. This is typically done in December or January when the colony is broodless and clustered. It is a simple, low-cost method suitable for beginners.
Sublimation (vaporisation): Oxalic acid crystals are vaporised inside the hive using a heated vaporiser, producing a gas that coats the bees and kills phoretic mites. This method allows repeated application at intervals (often every five days over three cycles) to catch mites as they emerge from brood. Sublimation