B-insights Table of Contents
Varroa destructor is considered the number one parasite of honey bees worldwide. In many regions, unmanaged varroa infestations are the main driver of winter losses and collapsing colonies.
For beekeepers, understanding what varroa is, how it lives, and how it damages colonies is the foundation of any serious management plan. This article explains the biology, symptoms and colony-level impact of Varroa destructor in clear, practical terms.
Note: This guide is for educational purposes. Always follow local regulations and product labels when using treatments in your hives.
What Is Varroa Destructor?
Varroa destructor is a parasitic mite that lives on honey bees and inside their brood cells. It is an external parasite: it does not live inside the bee’s body, but on the outside, feeding on bee tissues.
Originally, varroa lived on the Asian honey bee (Apis cerana). After jumping to the western honey bee (Apis mellifera), it spread across almost all beekeeping regions in the world. Today, most managed colonies must be monitored and controlled for varroa.
How Varroa Lives on Adult Bees
On adult bees, varroa mites:
Hide between the abdominal segments and other body folds
Feed on the bee’s fat bodies and haemolymph (the bee’s “blood”)
Move from bee to bee through contact inside the hive
A single mite on one bee may look like a small, reddish-brown oval spot about the size of a pinhead. Sometimes you see them on the thorax or on the side of the abdomen.
Life Cycle in the Brood Cells (Simple Version)
Varroa reproduces inside capped brood cells. The life cycle inside the cell can be simplified into a few steps:
A fertilized female mite (foundress) enters a brood cell just before it is capped.
The cell is capped with wax, trapping the mite inside with the bee larva.
The mite begins to lay eggs on the developing bee:
First an egg that becomes a male mite
Then several eggs that become female mites
The mite family feeds on the developing pupa.
When the adult bee emerges, fully developed female mites leave the cell on the bee and spread to others.
Because the mite reproduces inside brood, colonies with large amounts of brood and long brood rearing periods can support very rapid mite population growth.
Why Varroa Is So Dangerous
Varroa does more than “just suck a little blood”. It causes both direct damage to individual bees and indirect damage by spreading viruses and weakening the entire colony.
Direct Damage to Individual Bees
By feeding on bee tissues, varroa mites:
Reduce the weight and fat reserves of developing bees
Shorten the lifespan of adult bees
Weaken the immune system of both adults and brood
Can cause deformities when infestations are high
Infested bees may emerge weaker, less able to forage, and more likely to die early.
Varroa and Bee Viruses
Varroa is often compared to a “dirty syringe”. As mites feed on different bees, they can inject and spread various bee viruses, especially:
Deformed wing virus (DWV)
Other viruses that may not show obvious external signs
Because of this, colonies with high varroa levels often show:
Bees with deformed wings
Bees that cannot fly and crawl at the hive entrance
Gradually deteriorating colony health even before the mites themselves are easily seen
Colony-Level Impact
Over time, varroa infestations can cause:
Patchy brood patterns with many empty cells
Decreased brood rearing as the colony weakens
Fewer healthy foragers, leading to poor nectar collection
Increased winter losses as weak bees try to survive cold or poor conditions
In many regions, unmanaged varroa often leads to colony collapse within a few years, sometimes sooner.
How to Recognize Varroa Problems
Visible symptoms of varroa usually appear late, when infestation levels are already high. That’s why symptoms are not enough; colonies must be monitored. But it is still useful to know what to watch for.
Signs on Adult Bees
On adult bees you may observe:
Mites visible as reddish-brown spots on the thorax or between abdominal segments
Bees with deformed wings, short or crumpled
Bees that crawl in front of the hive, unable to fly
Bees that appear small, weak or trembling
Seeing even a few bees with deformed wings is a strong warning sign of serious varroa-virus pressure.
Signs in the Brood Nest
When you inspect brood frames, look for:
Spotty brood pattern: many empty cells where brood should be
Sunken or punctured cappings on brood cells
Occasionally, uncapped cells with white pupae where you may see mites present
These signs are not unique to varroa, but in combination with other clues and monitoring results, they strongly suggest mite problems.
Hidden Infestation: What You Don’t See
An important point:
By the time varroa symptoms are clearly visible, infestation is usually very high.
Many colonies can look “normal” while carrying mite levels that are already harmful. For this reason, regular monitoring is much more reliable than waiting for visible symptoms.
Basics of Varroa Monitoring
This article focuses on biology and impact, but effective varroa control always begins with measurement. You will cover full details in a separate article, but here is the basic idea.
Why Monitoring Matters
It tells you how many mites the colony has, not just whether mites exist.
It helps you decide if and when to treat.
It allows you to compare the effectiveness of your treatments over time.
Monitoring turns varroa management from guessing to informed decision-making.
Main Monitoring Methods (Overview)
Common methods beekeepers use include:
Sugar roll: collecting a sample of bees and dusting them with powdered sugar to dislodge mites.
Alcohol wash: collecting a sample of bees in alcohol and shaking to count mites more accurately.
Sticky boards: placing boards under screened bottoms to count natural mite drop.
Each method has its own procedure, advantages and limitations. These will be explained step by step in your dedicated article on How to Monitor Varroa Mites.
Understanding Infestation Levels
Monitoring results are often expressed as:
Number of mites per 100 bees (from sugar roll or alcohol wash)
Number of mites per day on sticky boards
Exact “thresholds” vary with region and recommendations, but the principle is the same:
higher mite numbers = higher risk and stronger need for action.
Overview of Varroa Control Options
There is no single magic product that solves varroa forever. Instead, beekeepers use a combination of chemical treatments and management methods over the season. Details belong in your treatment and integrated management articles; here is just a brief overview.
Always follow local laws and product labels when using treatments in your hives.
Chemical Treatments (High-Level View)
Common categories include:
Organic acids
Oxalic acid
Formic acid
Essential oil-based products
Thymol and similar substances
Synthetic miticides
Various active ingredients depending on region and regulation
Each has:
A preferred temperature range
Specific instructions about brood presence, dosage and treatment length
Possible side effects if used incorrectly
Because mites can develop resistance and products can stress bees if misused, it is important not to rely on only one product for many years in a row.
Non-Chemical and Management Methods
Good varroa management also includes non-chemical strategies, such as:
Drone brood removal (where appropriate and legal): removing capped drone brood, which mites prefer, to reduce mite populations.
Brood breaks or temporary queen caging: creating a period without brood so mites are more exposed to treatments.
Using more tolerant stock: where possible, working with bee lines that show better tolerance to varroa.
These methods are rarely enough alone in high-pressure areas, but they can support and reduce the need for heavy chemical use.
Integrated Varroa Management (IVM)
Integrated Varroa Management means combining:
Regular monitoring
Timely treatments using different modes of action over the year
Supportive management practices
instead of treating at random or only when visible symptoms appear.
A separate article on Integrated Varroa Management: Building a Year-Round Strategy will give you a model to plan treatments and checks across the whole season.
Common Varroa Mistakes to Avoid
As you start working with varroa, it helps to avoid some frequent errors:
Treating by calendar only
– Applying treatments on fixed dates without checking infestation levels.
Using the same product every time
– This increases the risk of resistance and may gradually make the product less effective.
Treating too late in the season
– Waiting until colonies are already very weak before intervening.
Ignoring weak colonies
– Collapsing colonies can spread mites to nearby hives through drifting and robbing.
Not reading and following labels
– Incorrect dosing, wrong temperature range or wrong treatment duration can harm bees and reduce effectiveness.
Your separate article Common Varroa Mistakes Beekeepers Make (and How to Avoid Them) will explore these in more detail, with practical examples.
Key Takeaways
Varroa destructor is a parasitic mite and a major global threat to honey bee colonies.
The mite reproduces in capped brood cells and feeds on adult bees, reducing their strength and lifespan.
Varroa is closely linked to bee viruses, especially deformed wing virus, which can seriously weaken colonies.
Visible signs (mites on bees, deformed wings, spotty brood) usually mean infestation is already high.
Regular monitoring is essential for making good decisions about if and when to treat.
Effective varroa control combines chemical treatments, management methods and careful planning across the season, rather than relying on a single product or a single treatment.
Effective management of Varroa destructor is critical for maintaining the health and productivity of honey bee colonies. Beekeepers must adopt an integrated approach that includes regular monitoring, timely interventions, and a combination of chemical and non-chemical treatments. Awareness of the biological impacts of the mite, alongside the symptoms and potential viral associations, empowers beekeepers to implement preventive measures and respond proactively to infestations. This multifaceted strategy not only mitigates the effects of Varroa but also enhances the resilience of bee populations against future threats.