The people were never informed of the impending attack. Note in the movie, Gen asks, "Why no air raid siren?" The ants were taking shelter. If the people had been able to take some shelter, much less carnage. So I think, whether or not in real life ants were observed taking shelter, the writer is saying, "Even the ants get a warning, but not people. We are lower than ants."
As to why ants would know in advance, it probably comes under the same umbrella as animals sensing an earthquake or hurricane, well before it's come. Probably artistic license.
It is of course very endearing that ants marching into the house is not met with repellant, swatter, or broom, but an innocent observation, a gentle reminder that life is amazing at any size.