If I could erase one thing from the history of beekeeping — one pest, one disease, one existential threat — it would not be American Foulbrood, though that disease is devastating. It would not be Colony Collapse Disorder, though that phenomenon terrifies us. It would be Varroa destructor.
The Varroa mite is not the only threat bees face. But it is the amplifier of all other threats. It weakens immune systems, shortens lifespans, and vectors a horrifying array of viruses that can collapse a colony in weeks. An untreated Varroa infestation doesn't just harm the bees — it creates a cascade of failures that makes every other problem worse.
American beekeepers didn't have to deal with Varroa until 1987. Before that, mites were Asia's problem — specifically, a problem for Apis cerana (the Asian honeybee), which had lived alongside Varroa for millennia and developed behavioral defenses (grooming, hygienic behavior) that kept mite populations in check.
Then Varroa jumped species to Apis mellifera (our European honeybee), a species with no natural defense against the parasite. The result has been catastrophic. Today, an untreated colony in North America will die within 1-3 years. Not "might die." Will die.
This is your enemy. Let's understand it.
Varroa mites are native to Asia, where they lived on Apis cerana (the Asian honeybee) for ages in a relatively stable host-parasite relationship. The bees groomed mites off each other. They preferentially removed infested brood. The mites reproduced slowly enough that colonies survived.
In the 1950s and 60s, global trade in bees (shipping queens and packages between continents) introduced Varroa to Apis mellifera hives. By the 1970s, Varroa was spreading through Europe. By the 1980s, it had reached South America and Asia. In 1987, it was confirmed in the United States — first in Florida, then spreading rapidly north and west.
Within a decade, Varroa was endemic across North America. Today, there is no Varroa-free state. No Varroa-free region. If you keep bees in the U.S., you have Varroa. The question is not "if" but "how many."
Varroa mites are tiny — about the size of a pinhead (1-1.5 mm) — but visible to the naked eye. They're reddish-brown, oval, and flat, with a crab-like body and eight legs. And they live in two distinct phases:
Phase 1: Phoretic (On Adult Bees)
A mated female mite clings to an adult bee, usually wedging herself between the abdominal segments where she's difficult to dislodge. She rides the bee like a parasite, feeding on the bee's hemolymph (bee blood — technically not blood, but functionally similar) and fat bodies.
This feeding weakens the bee, reducing her lifespan and impairing her immune system. But it doesn't kill her immediately. The mite can survive on adult bees for weeks or even months if no brood is present (as in winter).
The mite's goal during this phase: find a brood cell about to be capped.
Phase 2: Reproductive (Inside Brood Cells)
About 24 hours before a worker or drone cell is capped (sealed with wax), a female mite drops off her host bee and crawls into the cell with the larva. She hides beneath the larva in the pool of royal jelly, going undetected by the workers who come to cap the cell.
Once the cell is capped, the mite's work begins:
The male mite matures quickly (about 6 days), mates with his sisters inside the sealed cell, and dies. The female mites feed on the larva, mature (about 7 days), and wait for the adult bee to emerge.
When the bee chews through the wax capping and emerges, the mated female mites emerge with her — ready to repeat the cycle by finding a new host and, eventually, a new brood cell.
Here's a critical detail: Varroa mites prefer drone brood over worker brood by a ratio of about 10:1.
Why? Because drone brood takes longer to develop (24 days from egg to emergence, vs. 21 days for workers). That extra 3 days gives the mite time to lay more eggs. In a worker cell, a female mite can typically produce 1-2 viable daughter mites. In a drone cell, she can produce 3-4.
This is why drone brood frames are a useful diagnostic and management tool: inspect a frame of uncapped drone brood, and you'll get a clear picture of your mite levels. It's also why some beekeepers use "drone brood culling" as a mite control method (more on that in the next chapter).
If Varroa mites only fed on bees, they'd be a manageable nuisance. Annoying, yes. Harmful, yes. But not an existential threat.
The true horror of Varroa is that they are disease vectors. When a mite pierces a bee's exoskeleton to feed, it injects saliva (which contains anticoagulants) and often transfers viruses from previous hosts. These viruses, which the bee's immune system might otherwise suppress, now have a direct route into the hemolymph.
Deformed Wing Virus (DWV): The most visible and common. Infected bees emerge with crumpled, useless wings. They cannot fly. They crawl around the entrance, rejected by the colony, and die within days. If you see bees with deformed wings, your mite infestation is severe.
Chronic Bee Paralysis Virus (CBPV): Causes trembling, inability to fly, and eventual death. Infected bees are often hairless and shiny.
Acute Bee Paralysis Virus (ABPV): Kills bees rapidly — within days of infection.
Kashmir Bee Virus (KBV): Often asymptomatic at low levels but lethal when combined with Varroa-induced immunosuppression.
These viruses can persist in the colony even after mite levels are reduced. A bee infected as a larva may emerge healthy-looking but die weeks earlier than normal, spreading the virus to nestmates. The result: a slow, grinding collapse of the colony's vitality.
Let's walk through the math:
A single female mite entering a hive in April can produce 2-3 daughter mites per reproductive cycle. Those daughters mature, leave the cell, and reproduce. The population doubles roughly every 3-4 weeks during brood-rearing season.
By August, that one mite has become hundreds. By September, thousands. The mites feed on developing brood, weakening them. They inject viruses. Worker bees emerge stunted, short-lived, and unable to perform their tasks. Foragers die in the field. Nurse bees can't feed brood adequately. The population declines.
Meanwhile, it's fall, and the colony is trying to raise winter bees — those long-lived workers who must survive until spring. But the mite-infested brood emerges weak and virus-ridden. Winter bees die in December instead of March.
The colony dwindles. By January, it's too small to maintain the cluster. The bees freeze, or they break the cluster to reach food and freeze individually. By February, the hive is silent.
You open it in March and find: dead bees clustered on frames, full stores of honey (they didn't starve), and thousands of mites crawling on the corpses.
This is how Varroa kills. Not with a bang, but with a slow, inevitable erosion of the colony's ability to replace itself.
Studies show that an untreated colony — even a strong, healthy colony — will collapse within 1-3 years of Varroa infestation reaching critical levels. Not "might." Will.
Some beekeepers claim their bees survive without treatment. Sometimes they're right — for a year or two. But more often, they're simply witnessing the slow decline and attributing survival to their "natural" methods. Eventually, the colony dies or swarms (and the swarm, carrying mites with it, dies shortly after establishing).
There are no Varroa-resistant bees in North America (yet — breeders are working on it). There are no "natural" solutions that eliminate mites without intervention. If you do not test and treat, you will lose your bees.
"The beekeeper who says 'my bees don't need treatment' is either treating unknowingly, lying, or hasn't yet reached the third year."
— Randy Oliver, Scientific Beekeeping