Varroa & colony health
For most beekeepers, the single most important factor in keeping colonies alive through winter is managing the varroa mite. Left unchecked, varroa will weaken and eventually kill a colony, usually within a couple of seasons. The good news is that with regular monitoring and a sensible plan across the year, you can keep mite levels low and your bees healthy.
This is general beekeeping information, not veterinary advice. Treatment products, doses and rules vary by country and region. Always use a product that is approved for use on honey bees where you live, and follow the label instructions exactly.
What varroa is and why it matters
Varroa destructor is a parasitic mite about the size of a pinhead. The adult female is reddish-brown, flat and oval, and rides on adult bees or hides in brood cells. It is easy to spot once you know what to look for.
The damage is twofold:
- Direct feeding. Mites feed on the fat body and haemolymph of larvae, pupae and adult bees, shortening their lives and reducing their strength.
- Virus transmission. This is the real danger. Varroa acts as a vector for several viruses, most notably Deformed Wing Virus (DWV). As mite numbers climb, virus loads rise sharply, and you start to see bees with shrivelled, useless wings. A colony can collapse seemingly overnight in autumn, even though it looked strong in summer.
The varroa lifecycle
Understanding the mite's lifecycle explains why timing matters so much.
A mature female mite enters a brood cell just before it is capped, preferring drone brood (the larger cell and longer development time suit her). Once the cell is sealed, she lays eggs that develop into new mites alongside the developing bee. When the bee emerges, the mated daughter mites and the original mother leave with it.
This means most of the mite population is hidden under cappings at any given time. Two consequences follow:
- Mite numbers grow exponentially while there is brood to invade.
- Many treatments only reach the phoretic mites riding on adult bees, so their effectiveness depends on how much brood is present.
Monitoring: know your numbers
Never treat blind. Monitoring tells you whether you need to act, and afterwards whether the treatment worked.
Alcohol wash or sugar roll
These sample the mites on a measured number of adult bees (usually about 300 bees, roughly half a cup).
- Alcohol wash kills the sample but is the most accurate. Shake the bees in alcohol, filter, and count the dislodged mites.
- Sugar roll (powdered sugar) is non-lethal: coat the bees in icing sugar, shake the mites out onto a tray, and count. Slightly less accurate but the bees survive.
Express the result as mites per 100 bees (a percentage of infestation).
Sticky board (natural mite drop)
Place a tray under a mesh floor for several days and count the mites that fall naturally. Divide by the number of days to get a daily mite drop. This is the least invasive method and good for tracking trends, though weather and brood cycle affect the figures.
Drone brood uncapping
Because mites prefer drone brood, uncapping a patch of capped drone cells and inspecting the pupae gives a quick sense of infestation. This doubles as a control method (see below).
Treatment thresholds
Thresholds are guidance, not law, and local recommendations differ. As a widely used rule of thumb:
| Measure | Watch level | Act now |
|---|---|---|
| Mites per 100 bees (wash/roll) | 1–2% | Above ~3% |
| Natural daily mite drop | a few per day | tens per day |
Treat sooner rather than later in late summer: the winter bees raised in late summer and autumn must be healthy to carry the colony through to spring. Mite damage at that point does the most harm.
Integrated Pest Management across the year
No single tool solves varroa. An Integrated Pest Management (IPM) approach combines monitoring, husbandry and treatment, chosen to fit the season and the presence of brood.
Spring : Monitor early. Strong, building colonies can tolerate low loads, but check so you are not caught out.
Summer (active season) : Use cultural methods such as drone brood removal (cut out and discard capped drone comb to trap and remove mites) and consider splits or a brood break, which interrupt the mite breeding cycle.
Late summer / after honey removal : This is the key treatment window. Once supers are off, organic-acid and thymol-based products are commonly used. Formic acid can penetrate cappings and reach mites in brood. Thymol (a plant-derived treatment) works through the colony over a few weeks in suitable temperatures.
Autumn / broodless period : When the colony is broodless, oxalic acid (trickled or vaporised) is highly effective because all mites are then phoretic and exposed. Many beekeepers plan a midwinter broodless treatment as a reset before spring.
Rotate approaches where you can, monitor temperature limits for each product, and always re-check mite levels a couple of weeks after treating to confirm it worked.
Most varroa treatments must not be used while honey supers intended for human consumption are on the hive, as residues can taint the honey. Read the label for the required interval and follow it.
Other aspects of colony health
Varroa is the headline threat, but good general health helps the colony cope:
- Keep colonies strong and well fed; see Feeding.
- Replace old, dark comb periodically to reduce disease load.
- Watch for brood diseases and other pests; see Diseases & pests in the knowledge base.
- Some brood diseases are notifiable in many regions and must be reported to the authorities. Know your local rules.
Recording treatments in Openbeehive
Every monitoring count and every treatment is worth recording, both to track trends and to meet record-keeping rules that apply to beekeepers in many countries.
In Openbeehive you can log each application as a Treatment against a hive: the product used, the active substance, the dose, and the dates started and finished. Over time this builds a clear history so you can see what you used, when, and how the colony responded.
See Treatments for how to add and manage these records. Because the app is offline-first, you can log a treatment at the apiary with no signal and it will sync later.
Keeping accurate treatment records is often a legal requirement, especially where honey enters the food chain. Check the rules that apply where you keep bees.