6 Weeks...or 5 Months?
What creature has a very short life span in the warm months yet can live several times longer in the challenging cold of winter? That is precisely the reality for the worker bee.
The survival of bees during the winter is a story of epic preparation and a huge collaborative effort within the hive, from late fall to the onset of winter.
Worker bees that live in the warmer months have a hard and disciplined life ahead of them. From the moment they extract themselves from the cell to the last flap of their wings, they are aptly named workaholics. Their industry puts great stress on their tiny bodies and they use a huge amount energy in working so diligently.
The end result is a lifespan of around 6 weeks.
By comparison, the worker bee that lives through the winter months has a much more focused, singular role. Her sole objective is to see the queen through to the spring, at which time the queen can start laying eggs.
The winter worker bee is a bridge from one generation of the queen's offspring to another. Her reward for seeing the queen through this challenging period is the potential to live from early winter to spring.
Months, not weeks....
Stores for the Winter
We are used to seeing our bees venture away from the hive during the warmer months, but that is not an option during the winter. The temperatures are too low and other risks such as bad weather and starving pests simply make this impossible.
And so, bees prepare at great length for the oncoming winter by building stores of honey within the hive. This store represents their lifeline for reaching the spring and they are entirely dependent on having enough honey to see them through that period.
The amount of honey required to survive the winter depends on the depth and duration of the winter. In warmer climates, 30 lbs. or so may be adequate but the harsh, colder winters in the north may require as much as 100 lbs. That's a very considerable burden on the first-year colony.
Out With The Drones
There are a number of ways in which bees prepare for the winter. Their store of honey is a heavily protected resource and anything that limits how long it will last is considered a risk.
Drones are one such factor.
While they are clearly essential to the reproduction of the species, drones contribute very little to the actual running of the hive itself. Indeed, when it comes to the consumption of honey they are a negative drain on essential resources. Worker bees see this coming and as the winter approaches, they evict drones from the hive. The idea of carrying "passengers" who simply consume honey through the winter is simply not a viable tradeoff.
So out the drones go. It's a ruthless but essential process, including the physical eviction of drones by worker bees.
Along the same lines, expanding the number of bees in the colony as winter approaches makes little sense. Brood at this time translates into more mouths to feed. This isn't purely a factor of reducing the number of bees consuming the honey reserve, but also reflects the simple truth that in fall there is less nectar and pollen at this time of year anyway.
The net result is that brood rearing is lowered considerably, an intentional act on the part of the colony as it prepares for winter.
Getting through the winter is a very different challenge than life in the summer. Bees are extremely well adapted to their environment at the best of times and they change their body make up to prepare for the worst of times. Specifically, the approach of winter creates so-called fat bees. Fat bees are winter bees - bees that are much better suited to get through the winter, as follows:
- A compound called vitellogenin helps bees store food reserves in their body. This is far less necessary in the summer, when they can freely move to and consume food. But in the winter vitellogenin becomes more important so a fat bee has more.
- Lower levels of hormones
- Enlarged food glands
- Higher level of sugars and fats in their blood
The end result is indeed a fatter bee, but also one that is better able to tolerate and survive the cold weather of winter.
The Winter Cluster
With the preparation done and the cold months arriving, it's time for the colony to "bed in" for the winter. As with most things bee-related, what happens in the apparently still and quiet hive is rather remarkable.
The objective of the winter cluster is simple, namely to reach the spring with a healthy queen and enough workers to restart the foraging and expand the colony all over again. The principle resources they need are warmth and nutrition.
Bees are cold-blooded. However, somewhat unusually, they do not simply die off leaving nested eggs to continue the species through the winter. Neither do they hibernate. Instead they remain active all winter, eating and metabolizing honey throughout.
The queen is kept at a steady temperature by essentially being "hugged" by workers throughout the winter. The worker bees will form a cluster - hence the name - around her, enclosing her in a small but warm space. They "shiver" their flight muscles, which creates heat. Across thousands of bees this can create a considerable heat source.
There are some fascinating aspects to the winter cluster.
- Bees will be dispersed around the hive while the temperature is around 60 degrees
- When the temperature drops below that level, worker bees will start forming a cluster around the queen
- The center of the cluster, where the queen resides, will be maintained at a temperature of around 92 F
- The "tightness" of the cluster will be adjusted, according to the outside temperature, with a denser cluster being formed as temperatures drop
- To ensure that workers on the outside of the cluster don't succumb to the cold, there is a constant movement of workers from the outside to the inside of the cluster, effectively giving all workers a turn in the warmer inner cluster
- If the outside temperature passes above 50 F, bees will often take advantage to leave the hive and defecate, thus helping the cleanliness of the hive. These are called cleansing flights.
Staying warm is important but for continued warmth the bees need a source of energy throughout the winter. That is the purpose of the honey reserve they build.
The whole cluster will gradually move around the hive, as one, passing over and consuming honey they have previously stored, fueling their muscle-originated warmth. If temperatures are within certain boundaries, the cluster can move around and "jump" from one part of the honey-laden hive to another.
It is not uncommon, though, for the cluster to be stranded - not able to reach perfectly good honey they have stored because temperatures are too cold, even though they have exhausted resources in the area in which the cluster resides. The loss of a colony due to cold, with a store of honey just out of reach, is a sad demise for the colony.
The winter cluster is a remarkable process though which bees find a way to survive frigid weather, thanks to an extraordinary effort and planning in the warmer months.