The third revision post for BBKA module 6 honeybee behaviour covers syllabus item 6.4, which looks at the honeybee colony throughout the seasons.
6.4 The seasonal variations in population size of a honeybee colony and an explanation of such variations.
Winter to spring
In winter when the days are short and the nights are long, frost bites the air and snow covers the ground, the bees cluster together inside the hive to stay warm. As outside temperatures reach around 18°C the bees begin to huddle and as temperatures continue to fall the colony forms a small, tight ball around the queen. She may have stopped egg-laying completely, but there are still tasks for her workers in a broodless hive.
At the centre of the broodless cluster the bees vibrate their flight muscles to maintain a core temperature of around 21–24°C, while the outer edges are insulated by a layer of resting bees. The bees at the centre of the cluster take turns in changing places with the bees at the edges of the cluster, so everyone has a chance to stay warm! However, many bees will freeze to death during the coldest months of winter; 8°C is thought to be the lower lethal temperature at which a bee will die. Occasionally, on a clear, mild day, the bees will venture outside on a ‘cleansing flight’ to avoid defaecating inside the hive.
The bees tuck into their honey stores, because generating all that heat requires a lot of energy. ‘During the winter a colony will use an average of about 1kg per week just for heat production. (So do not skimp on feeding!)’ says Celia F Davis, The Honey Bee Inside Out.
The population of the overwintering colony is around 10–15,000 worker honeybees and the queen. In late January, as daylight hours increase, the queen begins egg-laying again and the workers raise the temperature for rearing the brood to about 34°C.
Spring to summer
The days grow longer and warmer and the plants begin to flower bringing nectar and pollen. The queen’s egg-laying depends on how much she is fed, so as the weather improves and more forage becomes available, particularly pollen for brood, the queen will lay more eggs. It may be as soon as late February or early March that honeybees are seen flying home laden with baskets of pollen to feed the spring brood.
This is a perilous time for bees. The old, overwintered workers are dying off as brood is increasing and new bees are hatching, but their winter stores are now very low. The colony relies heavily on fair weather to forage to feed the growing number of hungry mouths. Between January and March is when many colonies are most likely to die and beekeepers should keep careful watch.
As spring moves into early summer the queen may lay more than 1,500 eggs a day, including drones to mate with virgin queens. A healthy, well-fed colony should grow from strength to strength and vary from 30,000 to 40,000 individuals at the height of the season. The colony continues to build up from May to June, which is usually the swarming season, although they may swarm earlier or later than this.
The workers put the queen on a diet to make sure that she is light and slim enough to fly – as a result, her egg-laying drops a week or two before the swarm. Swarming causes the population of the colony to fall by about a half and this combined with the break in brood both before and after the swarm, while waiting for a new queen to mate, means that the remaining population must work hard to build up numbers and stores again.
Summer to autumn
The longest day of the year has passed and daylight hours grow shorter and cooler. The queen’s egg-laying slows, less brood is produced, fewer bees hatch and the shorter-lived summer workers are dying off. The colony is becoming much smaller in size.
Foragers can be seen bringing home red-jewelled propolis on their legs. This sticky, resinous substance exuded by trees is used to disinfect and insulate the hive as the colony prepares to overwinter. In early autumn, the drones, having served their purpose throughout spring and summer to mate with virgin queens, are evicted by their sisters who do not want to feed them in winter. The bees that hatch in autumn will live for almost six months surviving on summer stores.
The seasons turn full circle as temperatures begin to drop and the colony clusters together waiting for spring to return.
A great revision post from Emily Heath of Adventures in Beeland: 3rd Honeybee behaviour revision posts: the queen’s egg laying behaviour & seasonal variations in the size of a colony
Mid Buck Beekeepers Association Blog’s excellent revision notes for BBKA module 6
Celia F Davis. The Honey Bee Inside Out. Bee Craft Ltd, ISBN-10: 0900147075
Ted Hooper. Guide to Bees and Honey. Northern Bee Books, ISBN-10: 1904846513