You can make a nice ant trap from a piece of tupperware with small holes (too small for bees) drilled in it. Put a mix of equal parts water, grape jelly, and boric acid in the trap and let them take that back to the nest.
I would think the moat would work with just water. Can fire ants swim? Oh no, now I'm going to have nightmares about swimming ants coming after my hives.