Peggie Castle was originally cast as Joan Nelson, but had to pull out of the project shortly before filming began. She was replaced by Sally Fraser, who did it as a favor for director Roger Corman, a friend, even though she was five months pregnant at the time.
Paul Blaisdell, who designed, built and portrayed the alien in the movie, affectionately dubbed his creation "Beluah". It is easily the most popular monster of Blaisdell's oeuvre among his fans as well.
Paul Blaisdell's friend Bob Burns restored the costume when it came into his possession long after Blaisdell's death. The photographs of it in his book "It Came From Bob's Basement" reveal it to be beet-red in color.
Although usually referred to as a being a "cucumber" or another vegetable by fans, "Beluah" is actually supposed to be a fungus.
Among the numerous names the crew gave the monster were the Tee-Pee Terror, The Cucumber Critter, and the Carrot Monster.
Chocolate syrup was used for the Venus monster's blood in the finale where it gets torched.
Composer and musician Frank Zappa made a tribute to "It Conquered the World" in his album, "Roxy & Elsewhere" (1973). In the introduction of the song "Cheepnis", Zappa tells the audience that he loves monster movies. "And the cheaper they are, the better they are". Frank Zappa describes "It Conquered the World" as a perfect example of monster movie with its alien with an "inverted ice-cream cone head with fangs". Frank describes one special scene when the "monster came out the cavern" and he could see the technicians pushing the creature over the rail. "This is cheepnis", Mr Zappa concludes before playing the song.
In 1956, American International released this film on a double bill with The She-Creature.
Originally, "Beluah" was built as a squat, flat-topped creature, but when it turned out not to be imposing enough - and to actually be shorter than leading lady Beverly Garland - a tapering conical top was added to it.
Shot in five days.
The little bat-like creatures that the monster uses to control people would later be re-used in Corman's next film The Undead.