When they tell you that you can't have giant ants, they mean that you can't mutate a regular ant into a giant one. But could they evolve that way on their own?

Actually, that was the point of a SF story I read years ago, I think, in one of the Dangerous Visions anthologies.

This isn't the first time giant ants have appeared in (x, why?). For more giant ants, check out Ants vs. Spiders.

And then there are these: