Varroa Mites on Bees: What They Look Like & Life Cycle

Varroa Mites on Bees: What They Look Like, How They Live, and the Signs You'll Miss

Every new beekeeper is told to "watch for mites." Almost nobody is told what that actually means. Here is what a varroa mite looks like, why you will almost never see one on a bee even when the hive is full of them, how their life cycle works, and the signs that matter.

The short version

Varroa mites are reddish-brown, oval, about 1.1 mm wide, and spend most of their lives hidden under capped brood. By the time you can spot them on adult bees, the infestation is severe. The only reliable way to know your mite level is a wash.

What a Varroa Mite Looks Like

An adult female Varroa destructor is a flattened oval, wider than it is long, about 1.1 mm by 1.6 mm. On a bee it looks like a tiny reddish-brown or mahogany button, roughly the size of a pinhead, with eight short legs tucked underneath. Most people first notice one riding on a bee's back between the thorax and abdomen, but that is the mite's least favorite spot. They prefer to wedge themselves under the bee's abdominal plates, on the underside, where they are nearly invisible and can feed undisturbed.

Males are smaller, pale yellowish, and never leave the brood cell; you will only ever see them if you open capped cells. The pale immature stages look like tiny white or cream-colored dots inside a cell with a pupa.

Don't confuse them with bee lice (Braula), which are round rather than oval, sit on top of the bee, and are harmless, or with pollen grains stuck to a bee, which are the wrong color and don't have legs.

Why You Almost Never See Them

This is the part that costs colonies. In a hive with brood, roughly two-thirds of the mites at any moment are sealed inside capped cells, not on adult bees. The third that are on bees are mostly tucked under the abdomen. So when a beekeeper looks over a frame of bees and sees no mites, that tells them almost nothing. Colonies at 5, 8, even 10 mites per 100 bees, well past collapse territory, routinely show no visible mites to a casual inspection.

Seeing a mite on an adult bee is not an early sign. It is a late one.

The Life Cycle, and Why It Decides Your Treatment Plan

Stage	Where	What happens
Phoretic (dispersal) phase	On adult bees	A mated female rides on a bee for days to weeks, feeding on the bee's fat body through the soft membrane under the abdomen. This is the only time oxalic acid can reach her.
Cell invasion	Uncapped larva, just before capping	She slips into a cell with a 5th-instar larva and hides in the brood food at the bottom. Drone cells are preferred by a wide margin because they stay capped longer.
Reproduction	Under the capping	About 60 hours after capping she lays one male egg, then female eggs every 30 hours. The family feeds on the pupa together.
Emergence	When the bee emerges	Mother and mature daughters walk out on the new bee. Roughly 1.5 viable daughters per worker cell, 2–3 per drone cell. Immature mites and the male die.

Two things follow from that table. First, mite populations grow fastest when there is the most brood, which is why a colony that looked fine in June can be in trouble by August: mites roughly double every month during brood rearing. Second, any treatment that only kills mites on adult bees, which includes oxalic acid, must be repeated across the whole brood cycle to catch the ones emerging from cells. That is the entire reason our dosage and schedule guide changes the number of treatments by season.

What the Mite Is Actually Doing to the Bee

For decades the textbooks said varroa sucked bee "blood" (hemolymph). A 2019 study in PNAS (Ramsey et al.) showed that was wrong: the mite feeds on the fat body, the organ that stores nutrients, detoxifies pesticides, produces the proteins winter bees need, and runs much of the immune system. A bee that was fed on as a pupa emerges lighter, shorter-lived, worse at foraging and less able to fight off infection. And with every feeding, the mite injects viruses, chiefly deformed wing virus, straight into the bee.

The Signs That Matter

Early (only visible if you look): a mite wash above 2–3 per 100 bees. That is it. There is no other early sign.

Middle: mites visible in drone brood when you uncap a few cells with a fork; tiny white guanine specks (mite droppings) on the ceiling of empty brood cells; the occasional mite on an adult bee.

Late: bees with deformed wings; crawlers on the ground in front of the hive; a spotty brood pattern with sunken, punctured or chewed-open cappings; pupae pulled out of cells; a colony that seems to shrink week over week despite a laying queen. This cluster of symptoms is called parasitic mite syndrome, and a colony showing it can collapse in a matter of weeks. Our guide to why bees abscond or disappear walks through what that collapse looks like.

Don't Look. Count.

The Honey Bee Health Coalition recommends a mite wash at least four times a year, and treating above 1 mite per 100 bees in winter, 2–3 in spring and fall, and 3 at peak summer. It takes five minutes with an Easy-Check and half a cup of bees. Here is exactly how to do it.

Tools We Use (and Recommend)

Mite Monitoring: the Easy-Check mite wash, plus a capping fork for checking drone brood.
InstantVap Oxalic Acid Vaporizer: when the count says treat, this is how we do it in seconds per hive. See all InstantVap models. Lorob Bees is the primary US seller, with stateside customer service and warranty.
Oxalic Acid: EPA-registered EZ-OX.

Happy Beekeeping from the Lorob Bees Team

Written by Rob Pollock

Rob keeps bees in Baltimore, Maryland, and owns Lorob Bees. He built and repaired his own corded oxalic acid vaporizers for years before becoming the primary US seller of the InstantVap, and he still picks up the phone when one needs service. Oxalic acid vaporization is the thing he cares most about in beekeeping, because it's the treatment that keeps hives alive without breeding resistant mites. More about Lorob Bees.

Keep reading: Explore all Lorob Bees beekeeping guides — varroa, oxalic acid vaporization, pests and diseases, all in one place.

Sources

Ramsey S.D. et al., Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph, PNAS, 2019
Honey Bee Health Coalition, Tools for Varroa Management, 8th ed.
Peck D.T. and Seeley T.D., Mite bombs or robber lures?, PLOS ONE, 2019

General beekeeping information, not a substitute for the product label.