Carniolans (Apis mellifera carnica) are said to be closely related to Italians. That is not surprising as they are native to a small area south of the Alps, but east of the Italians territory.
Carniolans have gained in popularity in the U.K., presumably because of the problems with Italians. In some countries they have become the bee of choice, but I have spoken to beekeepers in those areas who tell me that getting rid of the native bees (mainly Amm) was a big mistake and there are moves to restore the situation to what it was.
These bees have evolved in an area where the summers are warm but short, with winters being long and cold. For that reason they are able to winter with small clusters to conserve food, with a very rapid build-up in the spring. I have seen combs of brood in the spring that in my opinion are very short of nurse bees to look after them and my concern is the larvae won't get adequate nutrition, possibly leading to chalk brood and European foul brood (EFB) that are known to be aggravated by poor nutrition. In summer the queens are prolific, needing double brood B.S. equipment.
As with other pure races I find Carniolans to be docile, but subsequent crosses to be rather bad tempered. My experience tallies with that of others with regard to their reputation for swarming heavily - inveterate being a common word. I have seen a colony headed by a young queen one year swarm early the next and both the swarm and colony have swarmed again the same year. I have spoken to beekeepers who say this can be selected out, but not according to beekeepers I have spoken to in countries where there is a high concentration of carniolans. If it is so easy to select out then why are carniolans still so swarmy?