A honey bee swarm may contain more than 20,000 bees including the workers and queen.
April through June is the time you are most likely to encounter a swarming by honey bees. The swarm looks like a large irregular shaped ball flying through the air. They will sometimes land on trees or shrubs in the yard or the wall of a house. We often get frantic phone calls when this happens. In fact, honey bees are usually quite docile when they are swarming and will seldom attack unless severely provoked.
A honey bee swarm may contain from 1,500 to more than 20,000 bees including the workers and queen. Overcrowding in the nest or an old or weak queen can cause a colony to swarm. They will land in temporary sites such as a tree branch or bush and stay there for up to 48 hours while the scouts search for a suitable place to build their hive. These include old nests, hollow trees or sometimes hollow walls, also ceilings or attics of homes. Swarms that land on trees or shrubs often move on after a short time. A swarm that lands on the exterior of the house may move into the structure if the scouts find an opening and suitable void.
Swarms that land on shrubs or tree branches can be removed by bee keepers. Not all bee keepers will remove wild swarms as they are afraid of introducing disease or parasites into their own colonies. Once a swarm has entered into the wall of a home, it is much more difficult to remove and the colony often has to be killed. It is very important that openings are sealed after a honey bee colony has been destroyed as the sites can be detected by a new swarm a year later. This new swarm will then move into the old nest site. I have seen this happen for 3 or 4 years in a row until the openings were sealed. Honey bee colonies that have been in homes for a long period of time will produce extensive combs and large amounts of honey. If the colony is destroyed, the honey can cause staining, odour problems and attract other pests if it is not removed. Sometimes walls or ceilings must be cut open in order to remove the hive.
Honey bee swarms are not dangerous and if they land in your yard will usually leave on their own. The only time they cause a problem is if they move into the structure of the house.