The fastest living thing is a fungus?
Well, it depend on how you measure speed, and what you count as movement but... interesting.
The speed here is needed to get out of the "zone of repugnance" so that the spores will land on good sweet grass eaten by herbivores.
Let's sing it together: "The cirrrrcle of life..."
From dust (made from crap) we come and to crap (which will turn into dust), we return.