Is powdered ant poison really deadly if you get a little bit on you?

No -- not deadly. The main active ingredient in most ants' toxins is Formic Acid. Being an acid, this is a corrosive and can be quite painful. Bu it would take a HUGE amount to be deadly to humans. This doesnt mean you should allow any to get on you. A small burn won't kill you, but it's not good for you.