Willis H. O'Brien and Pete Peterson began filming the special effects of this film in a large remodeled dressing room at the Tepeac Studios in Mexico City, but when money became tight they finished the picture in Peterson's garage in Encino, California.
That giant worm with the "octopus-like arms" seen in this film is a prop from the unused spider pit sequence from the original King Kong (1933).
The sounds of the scorpions are the same sounds as the ant chirps in Them! (1954).
The volcano shown at the beginning was Paricutin which erupted in 1943 and was active for about a decade.
The trapdoor spider that attacks Juanito in the scorpions' underground home is one of the original models left over from the famous deleted spider sequence in King Kong (1933)
Many of the screams heard are stock sound effects that can also be heard in many Republic movie serials.
While filming the stop-motion effects at Tepeac Studios, O'Brien and Peterson were assisted with miniature set construction by Ralph Hammeras, who was at the same studio filming the visual effects for The Giant Claw (1957).
A typical Willis O'Brien touch - in a long shot of the cage descending into the cave, a tiny stop motion bat flies across the screen. Only O'Brien would add another day's work to a scene where it would be barely noticed.
At the conclusion of the scene where Hank and Arturo have arrived in the village for the first time, and after Hank has given the baby Manuel to the parish priest and are preparing to get out of the Jeep, a bird can be heard chirping followed by a cat meowing. Although there are special effect sounds and music added to the audio track, it would appear that they were otherwise recording raw audio as they filmed with little post-production work to clean up environmental noise.
This film is mentioned in Stephen King's famous best-selling novel, "It."