Swarming can be both a good and a bad thing. As an event, it occurs naturally and usually results in a new colony being formed. A swarm takes place when a senior queen leaves a hive, along with half the worker bees. Swarming is usually caused by overcrowding of the hive, overheating due to poor ventilation or the old queen having reduced levels of pheromone. Swarming can be delayed by providing more space in the hive by adding supers, keeping a good airflow in the hive and checking constantly for swarm cells. Hive bodies can also be reversed after winter. Young colonies in their first year in a new hive are unlikely to swarm.
Cypress IPM screened bottom boards can help with the ventilation in a hive. Other options include using slated racks, vented inner covers and / or moving screens, to ensure that unobstructed airflow reaches all parts of the hive. If there s a lot of sunlight falling onto one part of the hive, considered relocating it or constructing a partial shade to prevent overheating and the bees getting agitated.
If you detect that a swarm is getting ready, immediately set about getting a new hive ready. Do not try to capture the swarm if it is too high up in a tree or near electrical equipment. If it can be captured, gently shake the bees into a container or cut the branch. Make sure to get the queen contained and most of the others will simply follow her. Keep the swarm well ventilated and transfer them quickly to their new home. In their new home, spray them with sugar water to keep them calm. Continue feeding with a 1:1 ratio of water and sugar till the hive is up and running and bees have started going outside to feed and return.