for flies and mosquitos, a sharp puff of breath usually sends them on their way
for wasps a good backhand in mid-flight usually works well -- they bounce off the ground and it gives their nasty attitude a little shock without actually killing them
for those pests that actually bite me (try to eat me), i kill them without remorse.
i used to let mosquitos and flies bite me without retaliation, but have come to the personal conclusion that this is stupid.. if i feel a bite then WHAM!
