As the weather gets cooler you might have noticed fewer pollinators flitting about. Did you ever wonder how they spend their winter?
Many species of bees only live through the winter in their larval stage—that is, as babies, in the nest that their mother has made for them, whether that’s a hole in the ground or in a tree branch. Bumblebee queens make a nest for themselves and spend the winter there.
But what do honey bees do when they get cold? The short answer is surprisingly human: they shiver.
We’re getting ahead of ourselves—but isn’t finding commonalities between ourselves and these tiny, hard working creatures fun?—so let’s go back to those warm summer months.
Worker bees are busily collecting nectar and pollen outside the hive, building wax cells and making honey inside the hive, and taking care of the queen and all the baby bees. Because they aren’t able to work outside the hive in cold temperatures, they have to make enough honey to last them all winter long.
A Primer on Bee Nourishment
To understand what bees need for overwintering, it’s helpful to know exactly what it is that bees actually consume for nourishment. The diet of bees is comprised of two main building blocks: pollen and nectar. From those two ingredients they make honey and what is known as “bee bread.”
Nectar is a sugar-rich liquid created by flowers to attract pollinators. Bees, wasps, butterflies, and other pollinators use nectar for the nutrients it provides and, in return, pollinate plants through the adherence and release of pollen—in other words, when drinking nectar pollen from one flower sticks to their bodies and will fall off on other flowers as the pollinator flies around, thus pollinating the plants from which it gains its food. In biology, this is referred to as a “mutualistic” relationship, or one in which two species work together for mutual benefit.
Pollen is a protein-rich powder comprised of the microscopic reproductive cells of plants. Without getting too technical, most pollen contains two types of cells: vegetative and generative. When a grain of pollen is deposited on a flower’s pistil—these are the stem-like protrusions found in the center of the flower—the vegetative cells creates a pollen tube that extends down through the ovary of the flower. Meanwhile, the generative cells have split into what are essentially floral sperm cells, which travel down the tube and fertilize the flower.
Bees can ingest nectar in its natural state. Honey bees actually have two stomachs—one for storing nectar to bring back to the hive, and one for ingestion. During flight, if a bee has need of it, some of the nectar will transfer from its storage stomach to its ingestion stomach so it can eat right there in flight! The bee’s storage stomach combines nectar with special enzymes that change its chemical structure—this is what will eventually become honey, and those enzymes are what keeps honey from spoiling.
When honey bees return to the hive, they transfer nectar mouth to mouth until it is stored in the wax cells of honeycomb. At this point the nectar is still a very thin liquid. It is the evaporation that occurs from the fanning of hundreds of honey bee wings that turns this nectar into the thick, pourable liquid we know as honey. Honey is mixed with pollen to create bee bread, a substance rich in protein and sugars that baby bees eat.
Preparing for Winter
In a sense, honey bees do nothing but prepare for winter. Honey bees have a natural hoarding instinct that encourages them to collect as much pollen and nectar as possible throughout blooming season. After all, weather can be unpredictable: there is no way to know how many too-cold-for-flying days there will be in any given winter, so bees have to prepare as much stored food as possible to last. This means hives will often have extra honey—a boon for beekeepers, since they can now harvest honey without harming the hive, especially if they monitor the hive throughout the winter to be sure their food supply is sufficient.
Every function of a worker bee during the spring and summer is vitally important for the upcoming winter. Foraging for pollen and nectar builds up food supply, much like harvesting from your own backyard garden. Inside the hive, wax comb is constructed and pollen and nectar deposited, sort of the bee version of canning tomatoes. Worker bees that are acting as “nurse” bees are feeding and caring for baby bees, some of which—the ones born at the very end of summer—will be doing the work of actually keeping the hive warm all winter long.
When discussing the lifespan of honey bees, most casual sources say a worker bee lives for a few weeks. That’s true—in the spring and summer. Bees born late in the season, however, will not only develop differently, they also tend to have a longer life span—up to five months! Scientists believe the longer life span may be because honey bees do less active work during the winter, but the differences in their bodies may also play a part.
Bees born at the end of the season develop more fat stores in preparation for winter, and also have larger glands for feeding larvae, which will keep baby bees healthy and able to begin working in the hive as they grow.
Surviving the Winter
As the temperature begins to drop, around 55°F (about 12°C), honey bees begin the process of settling in for the winter. If you’ve ever heard the phrase “huddle together for warmth,” you already have a good understanding of how honey bee colonies survive the cold. The honey bees will form what is called a winter cluster—essentially a big ball of bees—all facing toward the center of the colony, using their collective mass to hold in heat.
However, not all the bees are able to join this cluster. Because winter is a time bees focus on the survival of their queen and existing larvae, no mating activity occurs, and thus no drones are needed. Indeed, drones—whose only role is to mate with the queen—would only consume needed resources. Most drones die naturally in the fall, but those that don’t are, shall we say, “encouraged” to leave the hive by worker bees.
What happens inside the hive? Unlike hibernating mammals, whose metabolic activities (including heart rate) slow during the winter to conserve energy, honey bees are active throughout the season. However, instead of engaging in the usual spring and summer business of cleaning, foraging, and making honey, all of their energy is focused on staying warm and making sure everyone has enough to eat. This is where all those canned tomatoes—that is, wax cells filled with honey and pollen—come into play. With enough food stored up, bees can break into those cells and be nourished all winter long.
It takes more than just forming a cuddle puddle to stay warm, though. Worker bees vibrate their bodies to generate heat—in other words, they shiver. Incidentally, this same mechanism can be used to kill small intruders such as wasps. A cluster of honey bees can surround a wasp and vibrate together until they have raised the temperature high enough to kill the wasp. Pretty handy.
The center of the winter cluster ranges 90-100°F (32°-37°C), keeping the queen toasty warm throughout the season. The temperature at the outside of the cluster is much cooler, around 50°F, which is the lowest temperature at which honey bees are still able to move around. Once the honey has been exhausted in one area of the hive, the entire winter cluster moves together as a single unit to a new spot in the hive where they can access fresh honey.
As soon as the exterior temperature rises above 50°F (10°C), worker bees can begin venturing outside the hive to dispose of accumulated waste—a super important function for any animals with so many individuals living together in a small space. Once temperatures are back above 55°F, the hive returns to business as usual: foraging, mating, and beginning the long process of preparing the hive for the next winter. And, if the hive has been industrious—and lucky—enough to have plenty of extra honey in the spring, the hive might swarm.
Swarming is the natural way that honey bees split one hive into two, which can only happen for a large and healthy hive. In preparation for a swarm, worker bees will have constructed special cells for the larvae of potential queen bees. These future queens are fed only royal jelly, which causes them to develop into mature queens. Before they hatch, the existing queen will leave the hive with many of the worker bees in a tight swarm seeking a new nest. They leave behind a contingent of worker bees, queens ready to hatch, and, if possible, a ready supply of honey to jumpstart the blooming season.