What is a bee swarm?
Swarming is the honey bee’s method of colony reproduction. The old queen and about half of the worker bees leave their former nest and seek a new home, usually in the spring but sometimes at other times of the year when local conditions permit. To start the process, certain worker bees, called “scouts,” begin to canvass the surrounding territory for a potential new nesting site even before the swarm leaves its original colony.

A departing swarm consists of a large number of bees flying in a cloud that seems to drift along through the air. People not familiar with honey bees are generally frightened by such a mass, which can contain 5,000 to 20,000 bees, but unless a bee becomes tangled in someone’s hair, it isn’t likely to sting. The queen is in the group, but not leading it. Usually within 100 to 200 yards of the original hive, the bees alight on an object and form a cluster, which looks like a seething, fuzzy glob of insects. Sometimes bees fly from the cluster to collect water and food, but most workers leaving the cluster are scouts that search out potential new home sites for the swarm. When they return from a good site, they dance on the cluster to communicate the location of their find.

A clustered swarm of many bees may appear frightening, but most spring swarm clusters of European honey bees—the common honey bees in central and Northern California—are extremely docile. It takes quite a bit of stimulation, such as being hit by sticks and stones or squirted with a hose, to induce defensive behavior. The same may not be true for Africanized honey bees or for any swarm of honey bees that has run out of food, as these aren’t nearly as predictable and can be very touchy, even as swarm clusters.

Honey bees will nest in cavities having a volume of at least 4 gallons but prefer cavities around 9 gallons. Honey bees also prefer dark cavities with an easily defended entrance that is at least 9 feet from the ground. Hollowed-out trees are ideal sites. However, honey bees may nest in all sorts of cavities such as inside walls of houses; in or around chimneys; in outbuildings, fences, shrubs, water meters, utility boxes, barbecue grills, and soffits; or under decks. Within a few hours to a few days, the swarm’s scouts usually reach a consensus about the best available site. Then the swarm takes to the air one last time to move to the new home.

Once in flight, the swarm is guided by scouts and arrives at the new site. It forms a cluster around the entrance with many bees fanning their wings and releasing a chemical signal to guide the others. Then the bees enter their new home, somewhat slowly. This is what most people notice when they see bees clustered on a section of a building. Inside, the low humming sound of the bees ventilating their nest often can be heard. 

If the bees don’t find a new nesting location, they may begin producing beeswax and forming combs at the spot where the cluster formed, such as a tree limb, the overhang of a house, or another unusual place. These “exposed comb” colonies may exist until fall (or year-round in warm-winter areas), but robbing bees, hungry birds, and inclement weather usually put an end to these colonies and their combs.

Management:
The need for managing bee swarms or hives depends on the location and whether the bees are establishing a hive. Swarms moving on without establishing a hive aren’t a concern. However, bees establishing a colony in a home need to be removed.

Swarm clusters:
Swarm clusters—the correct term for swarms when they aren’t flying—are ephemeral by nature and therefore generally don’t need to be managed. Whenever the bees locate the proper new nesting site, the swarm will fly off to the new location. The bees usually leave a bit of beeswax at their clustering location, so appearances of additional swarms at that same place can be anticipated in the future.

History: 
The western honey bee, Apis mellifera Linnaeus, naturally occurs in Europe, the Middle East, and Africa. This species has been subdivided into at least 20 recognized subspecies (or races), none of which are native to the Americas. However, subspecies of the western honey bee have been spread extensively beyond their natural range due to economic benefits related to pollination and honey production.

Description:
Like all Hymenopterans, honey bees have haplo-diploid sex determination. Unfertilized eggs (no paternal genetic contribution) develop into drones (males), and fertilized eggs (both maternal and paternal genetic contribution) develop into females. Worker honey bees are non-reproductive females. They are the smallest in physical size of the three castes and their bodies are specialized for pollen and nectar collection. Both hind legs of a worker honey bee have a corbicula (pollen basket) specially designed to carry large quantities of pollen back to the colony. Worker honey bees produce wax scales on the underside of their abdomen. The scales are used to construct the wax comb within the colony. Workers have a barbed stinger that is torn, with the poison sac, from the end of their abdomen when they deploy the sting into a tough-skinned victim. This results in the worker bee’s death. The queen honey bee is the only reproductive female in the colony during normal circumstances (some workers can lay unfertilized male eggs in the absence of a queen). Drones are the male caste of honey bees. The drone’s head and thorax are larger than those of the female castes, and their large eyes appear more ‘fly-like,’ touching in the top center of the head. Their abdomen is thick and blunt at the end, appearing bullet-shaped rather than pointy at the end as with the female castes.

Biology:
In the honey bee colony, labor is divided among individuals based on caste and age. A drone’s only purpose is to mate with a virgin queen from another colony. The queen is the sole egg layer in the colony and is responsible for producing all of the colony’s offspring (up to 1500 eggs/day). Worker honey bees are thusly named because they perform all colony maintenance tasks. The cohesiveness of the honey bee colony is dependent on effective communication. Honey bees primarily communicate within the colony through chemical signals called pheromones. Workers, drones, and queens have various glands that produce pheromones. These pheromones include the queen mandibular pheromone that enables a colony to detect the presence of their queen, brood pheromones that signal the type of care required by the immature bees in the colony, and Nasanov pheromone that communicates the location of the colony to workers who may have been displaced in a colony disturbance.
 
One of the most notable honey bee behaviors is stinging. Stinging is a defensive behavior worker bees use to protect the colony. When a colony intruder is detected, guard bees release an alarm pheromone that elicits a defensive response by the colony. Moreover, when a honey bee stings, it releases alarm pheromone to attract more bees to sting the location that was stung. All worker honey bees die after stinging, and European honey bees rarely sting without provocation.

Life Cycle:
Due to their highly social life history, honey bee colonies can be considered superorganisms. This means the entire colony, rather than the bees individually, is viewed as the biological unit. With that in mind, honey bees reproduce not by producing more individual bees, but rather by producing more colonies. The reproductive process of creating a new colony is called swarming.
 
European honey bees typically swarm in the spring and early summer when pollen and nectar resources are plentiful. To initiate the swarming process, 10 to 20 daughter queens are produced by the colony. When the daughter queens are in the late pupal stage, the mother queen and about 2/3rds of the adult workers leave the colony and travel to a location where they will coalesce while they send scout workers in search of a place to establish a new colony (typically an enclosed cavity, like a tree hollow).
European honey bees are adapted to temperate climates, where there is only a short season with generous amounts of pollen and nectar available. For this reason, they typically swarm only once a year. The remainder of the spring/summer is devoted to collecting and storing enough nectar and pollen to generate the food stores needed to survive the fall and winter.

This behavior of resource hording is what makes European honey bees excellent honey producers. Nectar is collected from flowers and transformed into honey though enzymatic processes and dehydration within the colony. At this time, the honey is capped over in the wax comb where it can stay fresh almost indefinitely, depending on the original nectar source. Beekeepers and honey hunters may then collect this honey comb for human consumption.