Riccardo Freda would later claim that he abandoned this project so that Mario Bava, who he knew could be a good director, would have a chance to direct.
The Caltiki monster was made from cloth and tripe. Everyone working with the filming of the monster complained about the terrible smell it let out.
Flies were a problem during filming of the tripe-made monsters. Sometimes a fly would land on the monster during filming and it would reveal the actual size of it.
When Prof. Fielding escapes from the police station, watch for Mario Bava. He is dressed to look like a Mexican who is in the foreground. This is one of his rare appearances in one of his movies.
According to dates visible on the newspapers shown, the main action of the film takes place between May and June 1959.