Is it true that bees and wasps don't sting if struck by hand while they are in flight? Is it true that wasps don't sting if struck by hand while flying? I know of one person who claims to have done this at least 20 times and has never been stung. And out of curiosity (not that I'd want to kill them), what about bees?

I think what your friend advised is incorrect, or they are very lucky. According to "Bee and Wasp Stings" from the University of California Davis, they specifically state:

> Unless someone accidentally collides quite hard with or swats at a bee or wasp, it is not likely to sting.

Also, if you swat at some species, they are likely to become agitated, making the situation potentially far worse.