Will fiddler crabs eat ... ... ... ?

[BuschWacker]

I had a fiddler for about a month. It never came out from a hiding spot long enough to disturb anything. It never touched any of my zoas, or my frogspawn. It really only ever went for a wander after lights out. I fed it pellets for crabs. It would come out to grab them, then take them back to its hole to eat. Not sure why it only lasted a month. I read that is fairly normal.