Swarms are both a blessing and a curse. The blessing part is that when one can be harvested and put to work in an apiary. A secondary blessing is that a swarm issues (isnt that a quaint word?) at all. That means a colony is healthy enough to swarm, something all too rare in these days of increasing stressors on honey bees.
The first thing to do with a swarm is collect it. At times easy; sometimes impossible. Swarms high in the air can be collected with vacuum devices, long ladders, or heroic gymnastics. Most can be collected into bags, boxes, supers or whatever and transported to permanent housing. It is important to ensure that there is enough ventilation; putting a strong swarm into an air-tight container is a recipe for disaster! Swarms are generally the gentlest of bees, but if left exposed for several days they can become hungry and much more defensive. Always have a lighted smoker or a spray bottle of sugar water at the ready when working swarms.
The public relations aspect of swarm gathering shouldn'tt be overlooked. The macho image many beekeepers display while on the job probably does less than intended. It is best to collect the bees in a calm and respectful demeanor. It is also a good opportunity to educate onlookers.
Once collected and transported, a beekeeper can do many things with this bunch of bees. The deciding factor is often the size of a swarm. Large swarms, 4 or 5 lbs. Can easily run themselves. Smaller swarms, 1-3 lbs. Can be combined with other swarms for a large colony; or added to a large colony to boost its nectar and pollen gathering capability during a major flow.
To be safe, all swarms should be considered infested with both tracheal and Varroa mites and treated accordingly. The queen heading that swarm is from essentially unknown age and heritage. To be certain of the future of that new colony, requeening as soon as possible should be considered.
Gathering a swarm can be the most exciting activity a beginner or seasoned veteran can experience. No two calls are ever alike and no two swarms are the same.