A colony that swarms is generally strong, until it swarms. It is taking a tremendous risk. The swarm of potentially half the colony that left with the old queen has to start from scratch in building a new home, finding food to provision it for winter, and go through a declining population until the new brood begins emerging, at the earliest about three weeks after swarming. Often they also replace the old queen in the next couple months and run the same risk described later for the home colony in raising a replacement queen.
But the home colony has major risks before it. It will have one or more queen cells prepared. One or more virgin queens may also leave and take more of the colony's work force with them in after swarms. Eventually they will have one virgin queen who will kill any remaining contenders and then prepare for her mating flights. The colony now faces its greatest peril.
A virgin queen must mate within the first week of her life or she loses the capability. If there is a week of cool rainy weather like the one we have just gone through, she may not be able to fly from the hive to mate. In this case she becomes a drone layer since she has no sperm to fertilize eggs, necessary to produce female offspring.
It is also a dangerous flight for the queen. She is larger and slower than the average field bee and has a greater chance of drawing the attention of a predator such as a bird or dragonfly. Statistics of southern queen breeders show that a fair percentage of virgin queens disappear and never start laying within the mating nucs, generally attributed to loss on the mating flight.
Once the mated queen starts laying, the act of swarming has still caused a one to two week interruption in the brood cycle and thus the population will have a further declining period. A swarm thus significantly jeopardizes the colony's chance of survival.
A swarm generally takes with it any chance of excess honey production. A small colony needs all of its workers to help with the activities of raising new bees, gathering the food for immediate use including pollen and nectar, and guarding the hive entrance. This must continue with about the same number of participants as a large hive but it represents a much greater percentage of the workers, thus restricting the number available to gather the reserves for winter.
A beekeeper that has a hive that swarms thus loses most of the chance for profitability from the hive for that year. It is also one of the ways that we draw attention to our hobby from the neighbors, when they call to say that the swarm has landed on their front porch and appears to be moving into the soffet. Not a good situation!!
Some will tell you that they like swarming because they use it to replace winter losses and to propagate a line that has survived. Every beekeeper has their own philosophy but I want to prevent swarms from my hives. If I like the line, I want to breed from it at my choice, not the bees' choice.
How can swarming be prevented? I reduce swarming by providing them plenty of room and regularly replacing queens with young ones. A queen in her second year of live seems programmed to swarm. She needs to be young and active during the spring flow on Long Island to avoid swarms.
I feel the ideal is to replace the queens in late summer so that she provides a fall boost to the hive. Spring is probably the most convenient time to replace queens because of the lower population in the colony to search for finding the queen. What works best for you? I don't know but please, don't let swarming of neglected hives cause the enactment of dumb laws preventing beekeeping. Be a good Neighbor!