When we talk about preparing honey bee colonies for winter, we often hear about “winter bees.”
In colder parts of the United States and Europe, the concept is relatively easy to understand. As fall approaches, brood production decreases dramatically, the colony prepares for several months of cold weather, and a generation of longer-lived bees carries the colony through winter.
But what happens in the San Francisco Bay Area?
Our climate is Mediterranean. Winters are relatively mild, frost is limited in many locations, and honey bee colonies can maintain brood for much of the year.
Do we still have winter bees?
The answer is yes — but the transition is much more gradual.
What Is a Winter Bee?
A summer worker bee may live only a few weeks during periods of intense activity.
Winter bees are physiologically different.
They generally live much longer and develop greater nutritional reserves in their bodies. These reserves help them survive periods when the colony is producing fewer young bees.
One important component is the fat body, an organ that plays a major role in energy storage, immunity, metabolism, and the production of proteins such as vitellogenin.
Instead of spending their short lives foraging intensively, long-lived winter bees help maintain the colony until brood production increases again.
Winter Bees Are Not Created by Frost
It is tempting to think that cold weather produces winter bees.
That is not really what happens.
The transition is influenced by several factors, including declining brood production, changes in available pollen and nectar, shorter days, colony demographics, and seasonal conditions.
This distinction is particularly important in California.
Our colonies do not need freezing temperatures to produce longer-lived bees.
The San Francisco Bay Area Is Different
The Bay Area has a Mediterranean climate characterized by dry summers and relatively mild, wetter winters.
For honey bees, this creates a very different annual cycle from that experienced by colonies in places with long, freezing winters.
In many Bay Area apiaries, the queen may continue laying eggs during much of the fall and winter.
Depending on the location, weather, forage, colony strength, and genetics, there may be brood in the hive during most of the year.
This means we don’t necessarily see a sharp transition from “summer bees” to “winter bees.”
Instead, I prefer to think of it as a continuum:
Summer bees → longer-lived fall and winter bees → spring bees
The physiology and longevity of the workers gradually change as the colony adapts to seasonal conditions.
Why October and November Matter
In my apiaries, September can still feel very much like summer.
Temperatures can remain high and colonies can still be active.
As we move into October and November, however, forage conditions, day length, temperatures, and brood production begin to change.
This is when producing healthy, longer-lived workers becomes increasingly important.
For the beekeeper, the objective should therefore not simply be to have a large population of bees going into fall.
The objective is to have healthy bees with good nutritional reserves and low parasite pressure.
And this brings us to Varroa.
The Varroa Problem Is Even More Important in a Mild Climate
One advantage of our climate is that colonies can maintain brood for a large part of the year.
But that advantage comes with a cost.
Varroa mites reproduce inside capped brood.
When colonies maintain brood through much of the fall and winter, Varroa can also continue reproducing.
In colder climates, a natural brood break can interrupt this reproductive cycle. In the Bay Area, that broodless period may be short — or sometimes almost nonexistent.
This makes late-summer and fall Varroa management particularly important.
A colony may look strong in September and still enter fall with a dangerous mite population.
Healthy Winter Bees Start Before Winter
The condition of the bees emerging in fall matters.
If developing bees are heavily parasitized by Varroa or affected by associated viruses, simply having thousands of bees in the hive is not enough.
For me, this is one of the most important principles of fall beekeeping:
The goal is not just to produce more bees. The goal is to produce healthy, long-lived bees.
That means monitoring Varroa, maintaining adequate nutrition, checking food reserves, and making sure the colony has a productive queen.
Nutrition Also Matters
Late summer can be challenging for colonies in the Bay Area.
Our Mediterranean climate means that vegetation can be very dry before the winter rains return.
Natural pollen availability can decline at exactly the time when we want colonies to produce healthy bees for fall and winter.
This is why I pay close attention to both pollen availability and colony condition during this period.
Supplemental feeding can sometimes be useful when natural resources are insufficient, but I prefer to base that decision on what I observe in each apiary rather than feeding automatically.
A Different Way to Think About Winter in California
Beekeeping advice is often written for climates much colder than ours.
Applying exactly the same calendar to Northern California does not always make sense.
We have winter bees, but we should probably think less about a single generation of “winter bees” and more about the progressive production of longer-lived bees as the colony moves from summer into fall and winter.
Our mild climate allows colonies to remain active for longer.
At the same time, continued brood production gives Varroa more opportunities to reproduce.
That is the trade-off.
Understanding this local seasonal cycle helps us make better decisions about Varroa control, nutrition, queen performance, and colony management.
After all, successful beekeeping is not just about following a calendar.
It is about understanding what the bees are doing in your local climate.