THEM! is one of the earlier films to use radioactivity to create a monster of some sort. The team that made it is relatively unheard of, even among monster movie fans. But, it is nevertheless a very good film.
The setup to the film is done very mysteriously. It's an awesome film to watch when you have no idea that a shitload of ants are going to come later in the film. The characters at first think a torn apart trailer and general store are the work of some homicidal maniac that just has a strange taste. They find that someone is stealing shitloads of sugar and using formic acid as a weapon.
The origin of the monsters in this film is that an atomic bomb testing in '45 has given off a significant amount of radiation and mutated a mound of desert ants. These ants have gotten progressively bigger and the radiation has caused a significant change in a lot of their biology along with just making them huge.
The writer obviously did his homework on ants. One of the first encounters with one of these ants is dealt with by shooting the antennae and disabling it's senses. THEN someone unloads a machine gun into it, proving that they're not really that invincible.
As the film goes on, the characters find and attack a nest full of these bastards and then invade it to check and make sure that everything's dead. These scenes are actually about as gripping as they should be. And for 1954 American special effects, well done.
After this, the ants are GONE for what seems like a very long time until essentially the end of the movie when there's a quite impressive standoff between the military and a bunch of ants. The lack of sheer number of ants is excused by the period in which the film was made, but I would like to have seen more of the buggers.
As far as the rest of the film goes, there's not much to it. I learned some cool info on ants through the mini-documentary that they have in the middle of the film. This definitely showed that the idea had plenty of badass points. However, I still raise the same complaint to this film that I had with The Beast. There needed to be more meat on the bones of this film.
As a film bearing shitloads of monsters and another random light romance, this is a good film. And this film should be seen due to it's classic-ness. I was the only person in the room of about sixty film students to get a joke someone made about this film that was hilarious. Everyone else suffice to say missed out because they didn't check this out. Give it a watch just for the 'cool' factor.