THEM! (1954)

This begins as a mystery in the desert and escalates into a threat of worldwide proportions. The film is exemplary in using sound and atmosphere in the early stages, making this probably the definitive monster film of the fifties warning us about the possible dangers of the atomic era. It also benefits from an excellent James Whitmore performance, as a local cop caught up in the whole nightmare of giant insects - ants. Whitmore behaves as if it's all really happening and was one of the best actors around. He has great support from Edmund Gwenn as the scientific authority, Joan Weldon as Gwenn's daughter and fellow scientist, and very tall tough guy James Arness (just before Gunsmoke) as the FBI agent assigned to the 'case.'
There is also a one-scene role for Fess Parker just before Davy Crockett and a show-up by Leonard Nimoy, a decade before he first played Spock on TV.     William Schallert also shows up in a scene. Directed by Gordon Douglas. Many years later, Director Joe Dante created scenes for a make-believe film from this era called "Mant" (the scenes were in the film Matinee-1993). "Mant" was mostly a parody of THEM! and Schallert appeared in some of the scenes, playing a dentist.  BoG's Score: 8 out of 10

Spoiler:

Them Trivia: in the same year as THEM! was released, another film about killer ants also came out - The Naked Jungle. That one was less sci-fi and more jungle adventure, but was produced by George Pal, Mr. Sci-Fi of the fifties.