Part of the rich sci-fi/horror tradition of giant animals and insects on a rampage, "Giant Ant" movies are an important sub-genre that was very popular through the 1950s and 1960s in America.
Why were so many of these movies made? What's so fascinating about watching giant ants crushing buildings, terrorizing small towns, and basically knocking humanity down from its comfortable perch at the top of the food chain?
Well, it's a simple theme that ties into the post-World War II, Atomic Age fear of humanity inadvertently killing itself off by messing around with nature (through the deadly combination of unchecked scientific curiosity, hubris, and, of course, radiation.) It's a classic response to a feeling of childish irresponsibility on a cultural level: the fear, or even hope, that some giant parental avatar (like Mother Nature) will swoop down on us and punish us for our impertinence.
Them! (1954) is arguably the best-loved and best-known Giant Ant movie.