Your tank is not nature, it is a captive environment. In nature, the ADF would have stood a chance of getting away, for a start. I keep them as pets, they are intelligent (and adorable) creatures. It would have been terrified to be chased down and eaten alive with no chance of escape. You'd be better off trying to replicate a natural environment for them using plants or something.
I'm too squeamish to feed live prey - I've heard live worms are particularly nutritious to frogs, but I'm not sure I could go through with watching something be eaten alive when there are so many food alternatives.
Just curious as I obviously haven't tried it, but what is wrong with buying live food online?