A swarm is the natural mechanism that a honeybee colony uses to reproduce itself. When a colony is particularly prosperous, bursting with bees and honey (often between April and July), the old queen leaves the hive with around half of the bees in the colony, and tries to find a suitable place to make a new home. The old colony will typically produce a new queen, and continue to occupy its old site. The swarm will often settle temporarily, for a few hours to a day or two, while bees scout out a new permanent home.
If the swarm is easily accessible, a beekeeper can put it in a box and take it away to a suitable new home in a hive - possibly his own, or new members of the Association are often looking to get going with a swarm caught in this way.
To find a beekeeper able to collect a swarm of honey bees, there is a useful page on the British Beekeepers Association website, here. This will help you confirm whether or not the bees are honey bees, and if so, you can then enter your postcode to find a list of swarm collectors nearby.
Otherwise, please contact our swarm liaison officer, Robin Rimmer on 01722 711066 or 07824 886850, or Dominic Corcoran on 07879 228823.
If bees have settled in an inaccessible place, such as a cavity wall, or inaccessible part of the roof space, a beekeeper unfortunately will not be able to help. Insects other than honey bees, such as wasps or bumblebees only set up seasonal nests, but a honey bee colony can survive many years. Such a colony will either have to left alone, or made accessible by opening up the location. As a last resort, the colony can poisoned by a pest control service, followed by treating the area and entrance route with a strong smelling detergent such as Jayes Fluid, to mask the pheromones which otherwise would attract other colonies to the same spot. Note that Wiltshire County Council pest control will not usually poison bee colonies, due to the overall decline in populations of most bee species.