Winter Bees: What They Are & Why Colonies Die in January

Winter Bees: What They Are, When They're Raised, and Why Colonies Die in January

The most frustrating loss in beekeeping is the hive that went into winter heavy, populous and calm, and was a handful of dead bees on the bottom board by February with a full box of honey above them. It didn't freeze. It didn't starve. Its winter bees died of old age at three months instead of six, because they were damaged before they ever emerged.

The short version

Winter bees are a physiologically different bee, raised in late summer and fall, built to live for months on stored fat body. Varroa mites feed on exactly that fat body while the bee is still a pupa, and inject deformed wing virus while they do it. Damaged winter bees die in midwinter with no replacements coming. Your August and September mite count is the single best predictor of whether the colony is alive in March, and the fix is a fall oxalic acid vaporization schedule with an InstantVap, before the winter bees are raised, not after.

What Makes a Winter Bee Different

	Summer worker	Winter (diutinus) bee
Lifespan	About 4–6 weeks (roughly 35 days measured)	Several months (135–150 days measured; must last 6 months or more in the North)
Fat body	Lean; burns through reserves foraging	Enlarged; stores lipid and protein for the whole winter
Vitellogenin	Lower	High; drives longevity, immunity and the ability to feed the first spring brood
Job	Nurse, then forage, then die	Cluster, generate heat, then nurse the first brood in late winter

The switch is driven mostly by the end of the fall pollen flow and the shutdown of brood rearing, not the calendar. In most of the US the winter bee cohort is being raised from mid-August through October.

Where Varroa Comes In

A 2019 study in PNAS (Ramsey et al.) showed that varroa mites feed on the fat body, not hemolymph. The fat body is precisely the organ a winter bee depends on: its food store, its detox system, its vitellogenin factory, its immune reserve. A pupa that was fed on by a mite emerges as a winter bee with the tank half empty. And every mite feeding injects deformed wing virus, raising viral loads by orders of magnitude.

Randy Oliver puts it bluntly: a colony going into fall with a raging DWV epidemic has little chance of surviving the winter, because the cold-stressed, aging bees can't mount an immune response, and putting off treatment past the first of September can let the epidemic run past the point of no return. There are no replacement bees in December. Whatever damage the winter bees carry, they carry to the end.

The foundational field study (Dainat et al., PLOS ONE) found that colonies with low mite levels before and during the transition to winter bees had longer-lived workers, and that colonies treated in July survived where untreated ones died.

The National Numbers

The Apiary Inspectors of America / Auburn survey put US colony losses for 2024–25 at a record 55.6% annual, 40.2% winter, and USDA-ARS traced the commercial crash to deformed wing virus A and B and acute bee paralysis virus carried by mites that were resistant to amitraz in virtually every sample. The 2025–26 survey improved to 39.9% annual, but backyard beekeepers still lost 54.8% of their colonies over the year and 32.9% over winter. Roughly half of hobbyist hives, every year. Almost all of it is the story above.

The Fall Plan

Wash in early August. A mite wash before the winter bees are raised. Over 2–3 per 100, treat now, not after the honey comes off in October.
Treat across the brood cycle. With brood present, repeated oxalic acid vaporization catches mites as they emerge. Our dosage and schedule guide lays out rounds and intervals; our customers with heavy brood run every 3 days for 6–7 rounds.
Wash again in September. Confirm it worked and catch reinvasion from collapsing neighbors, which Cornell research shows can add 14 mites per 300 bees in three weeks from a robbed-out hive 300 m away.
The last 50°F day. When daytime highs drop below 50°F for good, the colony is broodless or nearly so and every mite is exposed. One vaporization that day is the cleanest treatment of the year, and with an InstantVap it takes seconds per hive through the entrance without breaking the cluster.
The first 50°F day. Repeat in late winter, before spring brood ramps up, and the colony starts the season nearly clean.

Winter Bee Myths

"It was strong in October, so it was fine." Damage to winter bee pupae is invisible in October. It shows in January.
"I'll treat after I pull the honey." If that's October, the winter bees are already raised. EPA-registered oxalic acid is labeled for use with supers on; treat in August.
"They starved; there was a cluster on empty comb." A small, mite-damaged cluster can't move to honey inches away in the cold. The mites made the cluster small.

Tools We Use (and Recommend)

InstantVap Oxalic Acid Vaporizer: the cordless, battery-powered oxalic acid vaporizer we use in our own yards to keep mite loads low, which is the single best defense against every problem on this page. See the Lite, Compact, Original and Turbo. Lorob Bees is the primary US seller, with stateside customer service and a warranty we stand behind.
Mite Monitoring: the Easy-Check mite wash. How to do a wash in five minutes.
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

Apiary Inspectors of America / Auburn University, U.S. Beekeeping Survey 2024–25 results, 2025
Apiary Inspectors of America, U.S. Beekeeping Survey 2025–26 results, 2026
USDA-ARS, Viruses from miticide-resistant parasitic mites are cause of recent colony collapses, 2025
Ramsey S.D. et al., Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph, PNAS, 2019
Dainat B. et al., Winter survival of individual honey bees and colonies depends on Varroa infestation, PLOS ONE, 2012
Journal of Economic Entomology, Impacts of Winter Storage Conditions on the Physiology of Diutinus Honey Bees, 2021
Randy Oliver, Scientific Beekeeping, Understanding Colony Buildup and Decline, Part 13d
Peck D.T. & Seeley T.D., Mite bombs or robber lures?, PLOS ONE, 2019

General beekeeping information, not a substitute for the product label. Always read and follow the label of any product you use in a hive.