The annual cycle for a honey bee colony is much easier to understand when you look at bees from the standpoint of their over-riding goal: survival of the species.
Throughout the year, honey bees respond to external cues provided by nature – they don’t keep a wall calendar inside their hive – and once you understand how honey bees reproduce, their two-season life cycle begins to make sense.
A year for a honey bee colony can be divided into two halves. One half is characterized by expansion, and the other by contraction. The half that is characterized by expansion begins soon after the winter solstice. Some research seems to indicate that honey bees respond directly to changes in the amount of daylight, while other research says that they don’t. But regardless of how it works, we know that brood rearing increases soon after the winter solstice, and decreases soon after the summer solstice.
Shortly after the winter solstice, many things happen inside the colony to increase brood production. For example, the workers begin to raise the temperature of the brood nest. These warmer temperatures stimulate the queen to lay eggs—just a few at first, but more and more as time goes on. Of course, keeping the colony warmer requires more honey stores just when those stores begin to be depleted. So the colony has to manage a very delicate balance of population-to-stores.
Why the expansion? Why now? The answer is simple: reproduction. The colony is preparing to capitalize on the window of opportunity to reproduce that will come in the early spring. How does a colony reproduce? By casting a swarm.
When a colony casts a swarm, the existing queen, and the worker bees they choose to go with her, leave the hive and find a new location in which to live. Their challenge is to create a new hive from scratch; they have to recreate all of the comb, propolis, pollen stores, honey stores, and new brood. They can take none of this with them except for the honey they store in their nectar crops before leaving as a swarm. So, enough bees have to leave with the swarm in order to have the critical mass to get this done. The number of bees that leave with the swarm is critical.
The remaining bees, in the original hive, have the challenge of making a new queen. This means that they will have a period of time where no new forager bees are being born. So, they have to be left with enough honey and pollen to feed the new brood that they will eventually start raising, and also carry them until the new ranks of foragers begin adding to the stores being brought back to the hive. So, the number of bees that are left behind is also critical.
Again, a very delicate balance. But, in order to provide both colonies with enough bees to make their separate existence viable, the original colony must begin expanding in size soon after the winter solstice.