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A new honey bee colony is formed when the queen bee leaves the colony with a large group of worker bees, a process called swarming. In the prime swarm, about 60% of the worker bees leave the original hive location with the old queen. This swarm can contain thousands to tens of thousands of bees. Swarming is mainly a spring phenomenon, usually within a two- or three-week period depending on the locale, but occasional swarms can happen throughout the producing season. Swarming is the natural means of reproduction of honey bee colonies.
Secondary afterswarms may happen but are rare. Afterswarms are usually smaller and are accompanied by one or more virgin queens. Sometimes a beehive will swarm in succession until it is almost totally depleted of workers.
Entomologists consider the colony as a superorganism. An individual bee without a colony cannot survive for long. The colony also needs a certain colony size to reproduce. In the process of swarming the original single colony reproduces to two and sometimes more colonies.
A swarm of bees sometimes frightens people, though the bees are usually not aggressive at this stage of their life cycle. This is principally due to the swarming bees' lack of brood (developing bees) to defend and their interest in finding a new nesting location for their queen. This does not mean that bees from a swarm will not attack if they perceive a threat; however, most bees only attack in response to intrusions against their colony. Additionally, bees seldom swarm except when the position of the sun is direct and impressive. So-called "killer bees" swarm far more often than regular honeybees. Swarm clusters, hanging off of a tree branch, will move on and find a suitable nesting location in a day or two. Beekeepers are sometimes called to capture swarms that are cast by feral honey bees or from the hives of domestic beekeepers.
The worker bees create queen cups throughout the year. When the hive gets ready to swarm the queen lays eggs into the queen cups. New queens are raised and the hive may swarm as soon as the queen cells are capped and before the new virgin queens emerge from their queen cells. A laying queen is too heavy to fly long distances. Therefore, the workers will stop feeding her before the anticipated swarm date and the queen will stop laying eggs. Swarming creates an interruption in the brood cycle of the original colony. During the swarm preparation, scout bees will simply find a nearby location for the swarm to cluster. This intermediate stop is not for permanent habitation and will normally leave within three days to a suitable location. It is from this temporary location that the cluster will determine the final nest site based on the level of excitement of the dances of the scout bees.
When a honey bee swarm emerges from a hive they do not fly far at first. They may gather in a tree or on a branch only a few meters from the hive. There, they cluster about the queen and send 20 - 50 scout bees out to find a suitable new nest locations. The scout bees are the most experienced foragers in the cluster. An individual scout returning to the cluster promotes a location she has found. She uses a dance similar to the waggle dance to indicate direction and distance to others in the cluster. The more excited she is about her findings the more excitedly she dances. If she can convince other scouts to check out the location she found, they may take off, check out the proposed site and promote the site further upon their return. Several different sites may be promoted by different scouts at first. After several hours and sometimes days, slowly a favorite location emerges from this decision making process. In order for a decision to be made in a relatively short amount of time (the swarm can only survive for about three days on the honey on which they gorged themselves before leaving the hive), a decision will often be made when somewhere around 80% of the scouts have agreed upon a single location. When that happens, the whole cluster takes off and flies to it. A swarm may fly a kilometer or more to the scouted location. This collective decision making process is remarkably successful in identifying the most suitable new nest site and keeping the swarm intact. A good nest site has to be large enough to accommodate the swarm (about 15 liters in volume), has to be well protected from the elements, receive a certain amount of warmth from the sun and be not infested with ants.
Swarming creates a vulnerable time in the life of honey bees. Cast swarms are provisioned only with the nectar or honey they carry in their stomachs. A swarm will starve if it does not quickly find a home and more nectar stores. This happens most often with early swarms that are cast on a warm day that is followed by cold or rainy weather in spring. The remnant colony after having cast one or more swarms is usually well provisioned with food, but the new queen can be lost or eaten by predators during her mating flight, or poor weather can prevent her mating flight. In this case the hive has no further young brood to raise additional queens, and it will not survive. As soon as an afterswarm (the second and subsequent swarm after the old queen leaves with the prime swarm) is established at a new location, the bees raise a new queen, or sometimes a replacement virgin queen is already present in the afterswarm.
Africanized bees are notable for their propensity to swarm or abscond. Absconding is a process where the whole hive leaves rather than splits like in swarming. Being tropical bees, they tend to swarm or abscond any time food is scarce, thus making themselves vulnerable in colder locales. Mainly for lack of sufficient winter stores, the africanized bee colonies tend to perish in the winter in higher latitudes.
During the first year of a queen's life the colony has little incentive to swarm, unless the hive is very crowded. During her second spring, however, she seems to be programmed to swarm. Without beekeeper "swarm management" in the second year, the hive will cast a "prime swarm" and may cast one to five "after swarms." The old queen will go with the prime swarm, and other swarms will be accompanied by virgin queens.
It is considered good practice in beekeeping to reduce swarming as much as possible using several techniques. Allowing this form of reproduction often results in the loss of the more vigorous division. The remaining colony may be so depleted and set back due to the brood cycle interruption that it is unproductive for the season. Beekeepers control swarming prior to the natural swarm time. They may remove frames of brood comb making nucs (nucleus or starter colonies) or by shaking package bees (usually for sale) from hives.
Swarming is to the beekeeper what losing all of his calves is to a cattleman. Beekeepers try to anticipate swarming and assist the bees to reproduce in a more controlled fashion by "splitting hives" or making "nucs." This saves the "calves" and keeps the "cow" in condition to accomplish some work.
Old fashioned laissez-faire beekeeping depended upon the capture of swarms to replenish beekeeper colonies and early swarms were especially valued. An old English poem says:
(Or possibly for the last line, "A swarm of bees in July, let them fly.")
Beekeepers who do not wish to increase their number of active hives may use one or more of many methods for swarm control. Most methods simulate swarming to extinguish the swarming drive.
Beekeepers who are aware that a colony has swarmed may add brood with eggs that is free of mites. Given young brood the bees have a second chance to raise a new queen if the first one fails.
There are various methods to capture a swarm. When the swarm first settles down and forms a cluster it is relatively easy to capture the swarm in a suitable box or nuc. There are also swarm traps with Nasonov pheromone lures that can be used to attract swarms. One method that can be employed on a sunny day when the swarm is located on a lower branch or small tree is to put a white sheet under the swarm location. A nuc box is put on the sheet. The swarm is sprayed from the outside with a sugar solution and then vigorously shaken off the branch. The main cluster, hopefully including the queen, will fall onto the white sheet and the bees will quickly go for the first dark entrance space in sight, which is the opening of the nuc. An organized march toward the opening will ensue and after 15 minutes the majority of bees will be inside the nuc. This capture method does not work at night though.
If the swarm is too embroiled in its perch so it cannot be dropped into a box or sheet, a skep can be suspended over it and gentle smoke used to "herd" the swarm into the skep.
Swarms may now be collected by a suction pump and the swarm will be sucked into a box. This way is easy and few bees are lost and none become angry.
Smoke is not recommended to calm a clustered swarm. Smoke will have the opposite effect on a clustered swarm as many bees will become agitated and fly about instead of settling down.
Encountering a bee swarm for the first time can be alarming. Bees tend to swarm near their hives or honeycombs, so if a swarm is visible then a nest is nearby. Swarms are usually not aggressive unless provoked, so it is important to keep a good distance from the swarm. Most beekeepers will remove a honeybee swarm for a small fee or maybe even free if they are near by. If the bees feel threatened, they will use their stingers and release a pheromone to alert the other bees of the threat resulting in a large bee attack.
Generally, a weak bee colony will not swarm until the colony has produced a larger population of bees. Weak bee colonies can be caused by low food supply, disease such as Foulbrood Disease, or from a queen that produces low quantities of eggs.
Usually a beekeeper or bee removal company will use a bee vacuum to capture the bees in a caged container so they can transport to a bee observation hive. While capturing the bees, smoke is used to calm the bees which makes it safer and easier to remove the colony.
Bee swarms can almost always be collected alive and relocated by a competent beekeeper or bee removal company. It is a common belief that a bee swarm should always be exterminated for safety reasons, but this is rarely necessary and discouraged if bee removal is possible.