Riccardo Freda later claimed that he abandoned the project so 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.
Flies were a problem during filming. Sometimes a fly would land on the monster, revealing the monster's actual size.
According to dates visible on the newspapers, the main action takes place in May and June 1959.
Even though the film is set in Mexico, it was shot entirely in Italy.