Answer:
Curtail me thrice I am a youth; behead me once a snake; complete I'm often used in truth when certain steps you'd take.
First you see me in the grass dressed in yellow gay; next I am in dainty white, then I fly away. What am I?
There is one in a minute two in a moment and none in a thousand years. What is it?
No matter how much rain gets on me, I won't get any wetter. What am I?
I tremble at each breath of air and yet can heaviest burdens bear.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?