Updated: October 2023
What happens to bees when the weather grows cold? Where do bees live in winter? Do bees hibernate in winter, and how do they survive the low temperatures and stormy weather?
We may still see bees around in the autumn on dry days, feeding from the flowers on ivy - Hedera helix, and pollinating autumn raspberries (and other late crops). But what happens then?
It really depends on the species, but in summary:
Given the many bee species in the world, there are of course, exceptions to those scenarios described above.
One key factor is climate: in exotic locations, species may be active throughout the year. In such circumstances, there remains sufficient abundance of the right kinds of foods to keep the bees active.
In cooler climates (rather than exotic locations) where there are far fewer flowers from which to feed in the winter, bees need to shelter from the weather and conserve their energy until the flowers are blooming again.
Below we'll cover in turn, more detail about the winter habits of:
(By the way, the overwintering behaviour of bees, is sometimes more technically referred to as 'winter diapause').
Here is a nice little quote that sums up the situation for many wild bees, including bumble bees:
As autumn approaches, fewer species of bumble bee are seen foraging. The natural lifecycle of bumble bees means that most of the colony will die, and only the new bumble bee queens will survive.
New queens will first mate with males, and importantly, feed to build up fat reserves ready for their winter snooze (hibernation).
Bumble bees do have a certain amount of tolerance for the cold, but could freeze at temperatures from around -7.1°C (see Can Bumble Bees Survive Cold Temperatures?).
Hibernation sites vary, but it seems most bumble bee species prefer soil banks (perhaps in an abandoned rodent hole) and slopes, and preferably in the shade or in a North West facing position (Goulson).
However, I have read reports of bumble bee queens being disturbed during their hibernation in soft potting compost in a plant pot, or in a pile of wooden logs.
They may also seek winter refuge in a compost heap or old pile of garden rubble and leaves.
In milder climates – and even in milder weather zones of countries such as the UK, bumble bees have been known to remain active through the winter, foraging on Mahonias or other late/winter blooming shrubs and flowers in public parks.
If winters are getting warmer, perhaps this should not surprise us.
But what about elsewhere?
In areas of South East Asia and South America, there are bumble bee species that have no annual life cycle that includes winter hibernation, and colonies can become rather large as a result, even reaching up to several thousand workers (Michener & Laberge 1954; Michener Amir 1977).
In Brazil, the species Bombus incarum can produce as many as
2500 new males and queens in a single nest!
(In the UK, bumble bee colony size varies, but will perhaps reach 150 – 400 workers.
In countries such as the UK, with its cool winters, some bees species (including solitary species - see bee sociality) may overwinter as mature adults, or as pupae.
Mining bees, such as the Ashy Mining bee, Andrena cineraria, remain underground as adults in their natal cells.
species are very tiny and may overwinter in hollow plant stems – something I
keen to remind gardeners of, as they begin to tidy up for the winter, especially if they are thinking of burning the plant stems!
encourage gardeners to leave the hollow
plant stems until the following year, or if necessary, leave the stems
corner of the garden out of the way.
Interestingly, according to the book The Bees In Your Backyard: not
all the young of species develop and emerge from the nest in the same year, and will remain in the nest through multiple winters:
In warmer climates, honey bees may be active all year, so that honey is essentially fuel for reproduction and swarming.
In cooler climates, honey bees become less active, but not entirely dormant (inactive), and honey (winter food stores) is vital to help sustain the colony.
When the temperature falls below 10 °C the honey bee queen and workers huddle together in their brood chamber, in a temperature regulating cluster called a 'thermo-regulating cluster.'
This is commonly referred to as a 'winter cluster'. By this time, there will be no males (drones) in the hive or nest.
Older worker bees will form the outside of the cluster, with the younger bees toward the middle. The clustering bees vibrate their wing muscles in a kind of shivering movement, which helps to generate heat.
The bees are also helped by their hairy bodies, because the fine hairs help to trap the heat, and this effect is magnified by the fact that there are lots of bees together, all with hairy bodies.
The colder it gets, the more tightly the bees form their cluster.
As younger worker bees in the middle of the cluster get warmer, they loosen the tightness of the cluster, allowing the warm air to circulate back to the older bees on the outer of the cluster. The outer temperature of the cluster is usually maintained at around 12 °C, but no less than 6 °C2.
In the wild, honey bees may be
more protected from the elements within the trunks of trees or caves, than they are in a man-made bee hive.
Indeed, some researchers are questioning whether what goes on in a honey bee hive in winter, reflects natural behaviour, or is simply a behaviour used by honey bees in order to cope with life in a man-made bee hive:
Mitchell makes the point that in a natural bee cavity such as a tree trunk, insulation is provided by the surrounding mass of the tree. (Indeed, I find it interesting that beekeepers of bygone years even used hollowed-out tree trunks in which to keep bees - see image below).
In a tree cavity, there is a large amount of natural insulation provided by the trunk itself, both above and below the colony, that can be virtually any thickness, but more typically ranges from three to five inches, which is about six times the insulation quality of a typical bee box provided by the type of conventional beehive used today.
It should be noted that Mitchell used his background in physics to compare the heat loss from a tree to that of man-made bee hives.
He found that a man-made box from a conventional bee hive will lose four to seven times more heat than a typical tree colony, and that some behaviors of the colony may even be driven by that fact!
(1) The Potential of Bee-Generated Carbon Dioxide for Control of Varroa Mite (Mesostigmata: Varroidae) in Indoor Overwintering Honey bee (Hymenoptera: Apidae) Colonies Rassol Bahreini and Robert W. Currie Journal of Economic Entomology 2015 108(5), 2153-2167
(2) Phillips EF, Demuth GS: Temperature of the honeybee cluster in winter. Bull US Dept Agric 1914, 93:1-16.
(3) Ratios of colony mass to thermal conductance of tree and man-made nest enclosures of Apis mellifera: implications for survival, clustering, humidity regulation and Varroa destructor Derek Mitchell Published online 2015