It depends on what you mean by a hard winter. Temperatures below 10 degrees F over at least a couple of weeks could significantly affect fire ant populations. Since we seldom see such sustained low temperatures in the Deep South, it is unlikely that low winter temperatures will affect fire ants in that area, but it's certainly a possibility at the northern extreme of fire ants' geographic range. Ultimately, cold winter temperatures will limit how far north fire ants can spread. Sustained cold temperatures in late fall or early winter might be expected to have a greater impact than later in the winter. Dragging heavy objects over colonies in fields during cold weather to expose the brood has not proved to be a useful tactic in reducing fire ant populations.
For more information, see FAQ #36361: "At what temperature is it too cold for imported fire ants to survive?"
