Back when I was about 11 or 12, that was the early 70's, there was a real absence of science fiction on tv. On Sunday nights channel 29 from Buffalo would broadcast some old science fiction movie from the 50's. I remember Them! very well from that time, it became one of my favourites of that genre.
Them! had nothing to do with aliens, it was giant ants, they grew to enormous size due to radiation. This was a common theme in the 50's because of fears of the Bomb and little understanding about atomic power. When The Incredible Hulk comic was created by Stan Lee, it was inspired by these crazy 50's radiation movies.
One of the things that struck me about the movie when I was young, there were two main male heroic protagonists, and one of them got killed at the end saving everyone. That really struck me, because it was the first movie I'd seen where the hero died, and it was a really forceful ending for me. Looking back with a bit more understanding of film history, this was a bit of Film Noir leaking into the sci fi genre of the era. These days that kind of thing is common, but back then it was really striking for me.
Next day I went out on the driveway and burned me some ants with my magnifying glass.