Bees sense sickness on human breath. I've heard before that sensitive people sense when someone is sick, but bees are probably more objective. The smell of garlic? No problem. Cancer? Check. Diabetes? Check. (Their apocrine glands are known to contain pheromones that retain information about a person's health that bee antennae can identify.) But if they don't like people to be sick, what then?
Doctors could use their dousing method. Oh, and their stings can even help to cure AIDS. Melitten, in the venom is what does it... Well, you can read about that here.