I married a monster from outer space (1958)
Young girl marries an alien who's race is slowly switching places with human males...the reason? Obviously to procreate, since their race has no females.
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Randall Blankenship commented
It! The Terror from Beyond Space" (1958) is a science fiction horror film directed by Edward L. Cahn. The film follows a rescue mission to Mars that brings back the lone survivor, Colonel Edward Carruthers. However, suspicions arise among the crew that Carruthers might be a killer or, as you mentioned, a monster from outer space. https://papas-freezeria.com
The plot involves the crew members trying to survive as they believe an alien creature might be among them, possibly responsible for the deaths that occurred on Mars. The tension builds as they attempt to figure out the true identity of the threat and how to deal with it.