Occasionally bees will swarm from their hive. When they swarm usually about 60% of a current hive will fly off with the old queen. The rest stay in their current location with a new baby queen. Sometimes the new queen is not even hatched before the swarm leaves the colony. This is the way bees reproduce a new colony. The swarm will begin to search for a new home which is sometimes only a short distance from the current hive.
A swarm of bees is normally not dangerous nor aggressive. Honey bees are only interested in defending their hive. While they are gathering pollen or in a swarming state they are much less likely to sting humans since they are not needing to protect an established hive.
Swarming bees will only search for a permanent location for a few days before deciding where the new home will be. If there is a swarm on your property for more than a couple of days then the risk to you is that they have found a place they consider to be a good one for making their new hive. At that point they will begin to defend the location. This location may be under your front porch or in a tree near your house.
Who do you call for help?
If you really are dealing with honey bees you can locate a local beekeeper to remove the colony without destroying them. While finding an exterminator in the phone book is easy, an individual beekeeper may be more of a challenge.
Finding a local beekeeper
Your best chance of getting someone to collect a swarm and removed it from your property is to locate a beekeeper who lives nearby. Trying to get someone from a large honey farm will be more difficult, or they will charge you a large fee since a single hive is not that valuable to them. An individual, hobbyist beekeeper will often remove the swarm for free since he gets the benefit of having a new colony of bees without having to pay for it.
You can try looking in your local phone book, however many individuals don't advertise their services. Next would be to take a trip to a local health food store. Health food stores will likely have honey on their shelves from a local provider since honey is most beneficial to the local population. Many of the health benefits of honey exist because it is made from the flowers and pollen in the area. If there is not a name and address on the jar of honey on the shelf, ask the store manager who they buy their honey from so that you can contact the beekeeper.
As a final source of information you can try calling your state's agricultural department. It may take a few phone calls, but they will eventually route you to someone in the department who knows all the beekeepers in your area who can help you with swarm removal.
Be patient with the beekeeper
Once you locate a beekeeper to remove the swarm they will try to get to your property as soon as possible. But be aware that this is usually not their full time job. They are hobbyist farmers who are providing honey to the world. While they love what they do, they often have other work and family obligations.
The process to remove a swarm or colony can sometimes take a few days. If it is just a swarm it may be as easy as scooping up the bees and dropping them into a hive box. The beekeeper will leave the box overnight and usually return the next evening to collect the hive. If the bees have been there several days and consider your front porch to be their new home, it could take several more days to remove them completely. In the end the beekeeper may also have to exterminate the ones that cannot be removed.