It's dignity.
Try to make a fly get away of your nose using your and, and do the same with a bee. What would happen?
The fly will fly away and even would return back to annoy you. But the case is completely different with the bee. It will quickly bite you that will cause its immediate death.
It's not so important for a fly if it was stirred by a hand or even chased to be killed. It will just run away. But it's a big insult against a bee's dignity just to be stirred by a hand. It will turn back, defend itself, attack, zzzzzzzzzzzzzzzzzz, it will sacrifice its own life to protect its dignity.
So, what is the reason behind this great difference?
It's all about the place where they live in. The ordinary place of a fly is dirt, rubbish and horrible smelling stuff. But the ordinary place of a bee is gardens, flowers and wonderful smelling roses.
People aren't so different from this little comparison between flies and bees.
Be a bee, not a fly.