Lesson 54: Varroa Mites

The most serious pest of honey bees, and why every beekeeper must manage them

If you remember only one pest from this chapter, make it this one. The varroa mite (Varroa destructor) is the most serious pest of honey bees, causing more damage and higher costs than all other bee diseases. According to the Honey Bee Health Coalition, every honey bee colony in the United States either has varroa mites now or will have them within a few months. And the overwhelming majority of colonies can't survive unless the beekeeper keeps mites from reaching damaging levels.

What varroa is

• A tiny, reddish-brown, oval mite, about 1.1 mm long and 1.5 mm wide, wider than it is long, like a tiny flattened tick. You can see it without a magnifier.
• An external parasite that feeds on adult bees, pupae and developing brood, mainly on their fat body, the organ bees rely on for energy and immunity, especially over winter.
• Originally a parasite of the Asian honey bee, which lives with it without much harm. In the 1950s it switched hosts to the European honey bee, and it arrived in the United States in 1987.

Why it's so damaging

• Mites weaken bees. Feeding on the fat body weakens bees and shortens their lives, especially the long-lived winter bees a colony depends on.
• Mites spread viruses. This is the biggest harm. Varroa transmits several deadly viruses, including deformed wing virus (lesson 62). Virus levels rise with mite levels, so controlling mites is also how you control viruses.
• Colonies collapse. An untreated colony's mite population grows through the season. Colonies with high mite loads in the fall are much more likely to crash and die over winter. A collapsing colony can also spread mites and infection to other colonies as its bees drift or are robbed.

How varroa reproduces

Understanding the mite's life cycle explains how to control it:

1. A female mite (the "foundress") slips into a brood cell just before the workers cap it, and hides in the larval food.
2. After the cell is capped, she feeds on the developing bee and lays eggs. Her first egg becomes a male; the rest become females, which mate with him inside the cell.
3. When the bee emerges, the mother mite and her mated daughters come out with it and ride on adult bees, mostly nurse bees, which carry them to more brood cells.

Drone brood is their favorite. Drone cells are capped longer (about 15 days vs. 11 for workers), so mites raise more offspring in them, about 2–3 daughters per cycle versus 1–2 in worker cells. Mites are found far more often under drone cappings. Mites don't reproduce in queen cells.

Why timing matters: most mites are hidden under brood cappings whenever there's brood, where many treatments can't reach them. Mites on adult bees are called dispersal (or phoretic) mites. During broodless periods, all the mites are on adult bees, which is when some treatments work best.

The seasonal pattern

Mite numbers rise and fall with the bee population, but lag behind it. Through spring and summer the mite population grows steadily. When the colony cuts back on brood in late summer and fall, mites become concentrated on the remaining bees, just as the colony is raising its winter bees. Keeping mites low at the start of that fall decline is critical.

Signs of a serious mite problem

By the time you see these signs, mite levels are usually already well above the treatment level:

• Mites visible on adult bees (on the back or abdomen) or on drone pupae when you uncap cells.
• Bees with shriveled, deformed wings (deformed wing virus; lesson 62), and bees crawling at the entrance.
• Spotty brood, with sick, discolored or dead larvae and uncapped cells, sometimes called parasitic mite syndrome.
• A dwindling colony, especially in late summer and fall.

Don't wait for signs. Monitor mite levels regularly (lesson 55).

How it looks: Varroa mites (reddish-brown ovals) on a developing bee.

A worker with deformed wings and a varroa mite, a sign of a serious infestation.

Dead bees with mites: the result of an uncontrolled infestation.

What to remember

• Varroa is the #1 threat to honey bees. Nearly every colony has them; untreated colonies usually die.
• Mites weaken bees and spread viruses (especially deformed wing virus).
• They breed under brood cappings, preferring drone brood; many treatments can't reach them there.
• Mite levels peak in late summer and fall. Keep them low going into fall to protect the winter bees.
• Visible signs mean it's already bad. Monitor regularly.

Quick check

1. Why is varroa so dangerous, beyond feeding on bees?
2. Why do mites prefer drone brood?
3. When in the year is controlling mites most critical, and why?

Adapted from: USDA Agricultural Research Service, Varroa Overview, Varroa Mite Life Cycle and Reproduction and When to Sample; Honey Bee Health Coalition, Tools for Varroa Management (9th ed., 2026) and Varroa Management; Penn State Extension, Methods to Control Varroa Mites (2025); UGA Bee Program, Honey Bee Disorders: Honey Bee Parasites; USDA, Diagnosis of Honey Bee Diseases (AH-690, 2000); UF/IFAS Extension, Welcome to the Apiary! (4H446).

Photos: varroa on pupa, Gilles San Martin, CC BY-SA 2.0 · bee with DWV and varroa, Stefan de Konink, CC0 (both via Wikimedia Commons) · dead bees with mites, blumenbiene, CC BY 2.0 (via Flickr).

Adapted from university Extension sources. Experienced Georgia beekeepers are reviewing these lessons. See something that doesn't match your experience? Tell us.