Translation:Five ants are more than four elephants.
I wanted to point out that without saying what they're more of, I would probably be inclined to say, "Five ants is more than four elephants," since we're talking about quantity. Frankly, I'd go so far as to say that the version with are sounds wrong to me, but others might disagree, since then I'd expect the more to be modifying something.
I am with AmbassaorTigger - because we may well be saying that it's "more" as in, more effective, a greater force to be reckoned with, or whatever it is, it basically makes the ants into a group. So, because you would say "A group of five ants is bigger than a group of four elephants.", it is sort of sounds as if that's what's being implied to me and so "is" sounds more natural.