There are far more terrifying things in flood waters than fire ants, starting with sewage and bacteria, moving on up to animals driven mad from drinking the water, and then on to stepping into a bloated dead corpse.

I remember the cows that went mad from drinking salt water post-Rita and thinking that I'd take a zombie attack over insane dying cows screaming while wading through the bloated corpses of the herd's dead.

At least the ants are quiet, don't stink, and are frankly more motivated to stay alive by retaining their ball than to pursue you. They're way more of a threat to floating bodies (and the people recovering or disposing of those bodies) than to living evacuees.